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Mazda RX-7: Part 2

By Shiv Pathak

In the first installment of our Project RX-7 series, we covered the performance-related strengths and weaknesses of a bone stock RX-7. In this installation, we will focus on preparation and taking the precautionary measures necessary to make Project RX-7 a streetable and reliable road racer. To address these requirements and plan our series of upgrades, we took our Project RX-7 to Mostly Mazda in Concord, Calif. Visiting Mostly Mazda is quite a visual experience. Arranged neatly in their parking lot are more than a dozen shiny RX-7s. Primarily of third generation ilk and few of race-prepped variety, the colorful fleet of rotary powered sports cars appropriately describes Mostly Mazda's professional expertise.

Modification Caveats

According to Brian Richards, the owner of Mostly Mazda, the third generation RX-7 can be a very reliable automobile. However, as an ultra-sophisticated, lightly disguised, rotary-powered race car, it demands special care. Before modifying the RX-7, one must become aware of its unique subtleties. One characteristic of the RX-7's unusual powerplant is its absolute intolerance to detonation. Unlike most conventional reciprocating engines which are able to withstand the abuse of knock, rotaries can fail (or at least become seriously compromised) with just a single, serious ping. This is one reason that rotaries are designed to run exceptionally rich air/fuel mixtures compared to their piston-laden counterparts. The RX-7, like most OEM turbocharged cars, is equipped with an electronic knock sensor that keeps a constant vigil for the tell tale signs that usually lead to knock. Although Mazda has taken many precautions to keep the 13B running reliably and trouble-free, the powerplant is anything but foolproof-- especially in the hands of an inexperienced tuners. "The FD (Mazda's designation for third generation RX-7) comes equipped with a MAP (Manifold Absolute Pressure) sensor, not a typical MAF (mass air flow) sensor" states Brian, "This mean that the stock ECU does not readily compensate for increased flow caused by exhaust back-pressure reductions or a intake upgrades. Reading only manifold pressure , the stock ECU relies on fixed maps that no longer deliver the required fuel for the increase in volumetric efficiency. Under this situation, a momentary lean-run condition can easily lead to detonation and apex seal damage."

Another potentially disastrous complication that plagues many over-enthusiastic shade-tree mechanics has to do with the FD's sophisticated sequential twin turbocharger system (see technical side-bar). Tuned carefully by the bright engineers at Mazda, the twin-turbo system offers nearly seamless power output from idle to redline. Controlled by numerous solenoids, countless vacuum lines and various mechanical actuators, the turbo control system is designed to deliver a consistently safe boost pattern and optimal driveability. However, problems immediately arise when cats get gutted, intercoolers upgraded, and free-flow exhausts installed. Since the boost control system operation relies on manifold pressure and exhaust back-pressure, a dramatic change one or the other can result in a severe over-boost situation. Brian comments, "This problem becomes most obvious during the transitions to the secondary turbo when boost pressure can momentarily spike several PSI. This short-term spike can lead to detonation and, almost always, blown motors." Similarly, a denser, cooler intake charge, from the use of more efficient intercooler units, can contribute to lean-run conditions if not met with appropriate EFI system modifications. For this reason, Brian suggest that even a relatively simple bolt-on upgrade is best accompanied with appropriate boost, timing and fuel re-mapping.

So what about all those RX-7s that only sport the "latest and greatest" bolt-on upgrades with no attention to ECU modifications? According to Brian, although these cars seem to be perfectly functional under short to medium-term use, they are often 'ticking time bombs', waiting for the right set of circumstances to self-destruct." Brian recalls several mildly modified RX-7 that have been towed to his shop suffering from blown apex seals. "Most people just don't realize how necessary it is to have a margin of safety associated with these engines," Brian remarks, "One owner who lived in northern California had an RX-7 with a free flow exhaust, intake and intercooler upgrade. With the stock fuel and boost management system, it ran a little on the lean side. For several months he drove the car to work every morning with no obvious problems. Finally, on an unusually cold, winter morning, the engined leaned-out and pinged once under boost. When he came to stop, the idle was lumpy and his motor was toast." As an experienced road racer, Brian knows the importance of long term durability. A minor engine problem can mean the difference between first and last place. Mostly Mazda's goals is to improve reliability while still offering competition-like levels of performance. Although many may view his upgrade precautions as excessive, Mostly Mazda's performance record on the race circuit and on the road speak for itself. Starting in Part III of this series we will begin our power-enhancing upgrades, carefully following Mostly Mazda's upgrade stages.

Thermally Challenged?

It doesn't take much time for a new RX-7 owner to realize that the RX-7 twin turbocharged rotary engine generates enough under-hood heat to warm a small Icelandic village. In fact, after a long drive, only select Buddhist monks capable of carrying a red hot cauldron by their forearms are able to lift the front hood and prop up the support without yelping in pain. How did Mazda ever expect to sell this car to an owner whose idea of self-sacrifice is a self-serve gas station? While not blistering enough to melt the clear coat off the hood and fenders, the under-hood temperatures are hot enough to prematurely age and harden the rubber hoses and lines in the engine bay. With the help of Mostly Mazda, this is another area we will focus upon in our series. Another "soft spot" in the RX-7's armor is its cooling system. As we have seen in Part I of this series, our on-track testing at Thunderhill raceway made the car run uncomfortably hot under the collar. To our dismay, a quick inspection of the engine bay reveals a relatively small-capacity radiator. Egad! Why such a puny radiator in an automobile that Mazda advertisers used to call a "race car for the streets?" Just in case its meager dimensions were not bad enough, unlike most radiators which mount vertically to receiving maximum air flow, the FD's unit is mounted with its bottom slanted backwards at a nearly forty-five degree angle! Although equipped with appropriate ducting to channel its share of air, much of the radiator is obscured by a large AC condenser unit. While we think much of the RX-7s overheating problem could be ameliorated by the removal of the AC system, we feel that doing so would destroy much of the RX-7 everyday utility during our highway cruises to and from the racetrack. In other words, why should we profusely perspire and dread trips to inland California just because Mazda didn't want to spend the extra bucks to use a more efficient radiator? A bit of research suggested that we weren't the only ones who have complained of overheating third gens. In fact, most of Brian's customers who engage seriously in track events experience cooling problems. We will attempt to eliminate Project RX-7's overheating tendencies with a little help from Mazda Competition's parts bin. We will be installing their larger capacity race radiator in the Part III of our series.

Getting Started

The first step in any project is proper preparation. These precautions are perhaps the best insurance against mishaps during your upgrade process. These maintenance items should be regarded as mandatory, not optional. As with any new (or used) car, the first stage in maintenance involves changing all vital fluids. This is especially critical for our purposes since the car will be required to perform under full loads for extended periods of time. Until our racing radiator is installed, we make the best of our stock cooling system by flushing and replacing the coolant mixture. Mostly Mazda recommends using a 70/30 mixture of distilled water and coolant. We also added the recommended dosage of Redline Water Wetter to further improve heat dissipation. Using only water is not recommended and is potentially damaging to the water pump mechanicals due to its insufficient lubrication and anti-corrosive properties. Dino or Synthetic motor oils? That's the big question. While Mazda Corp. has officially forbid the use of synthetic motor oils in their rotary engines, Mostly Mazda strongly recommends the use of Redline synthetics products, in the motor, differential and in the transmission. The unofficial "inside story" behind Mazda's statement is quite interesting. Apparently, in the early 1980s, Mazda's racing team had lubrication problems using a certain brand name synthetic motor oil. Instead of disclosing the particular oil brand and potentially getting faced with a lawsuit, Mazda made an unfair general statement, suggesting that all synthetic oils were incompatible with their rotary engines. Redline motor oils have been successfully used in rotary race motors for nearly two decades. Their motor oils offer improved film strength over other motor oils, synthetic or non-synthetic. Synthetics also extend the life of the turbochargers by resisting bearing "coking" typically associated with traditional oils. We used Redline 10W/40 high performance motor oil for Project RX-7. At over six dollars a quart, it is hardly inexpensive. However, a good motor oil is the best insurance against premature engine wear. Evidence supports that synthetic oils may not burn as cleanly as dino oils. According to Mostly Mazda, this residue may potentially cause premature clogging of the catalytic converter over a very long period of time. This relatively minor problem is easily remedied by catalytic converter replacement. Such maintenance is far less expensive and time consuming than replacing engine or turbo damaged by insufficient lubrication.

Fuel related problems can also bring a quick death to the RX-7. Brian has seen many blown rotary engines caused by something so trivial as a dirty fuel filter. The stock fuel filter, while sufficient to support a 140 horsepower Miata for 60,000 miles, needs to be replaced more frequently in the turbocharged RX-7. Brian strongly recommends the replacement of the fuel filter every 15,000 miles. As seen in the photographs, the fuel filter is located well above the rear differential, making it very difficult to find, let along replace. In fact, it is often neglected by owners and sometimes avoided in regular dealer maintenance. Again, we viewed replacing the fuel filter as cheap insurance against fuel related problems.

The next stage of preparation is much more time consuming but equally important for longevity and performance. Under the manifold, there exists a proverbial "rat's nest" of seventy-six vacuum lines controlling, among other functions, the sequential operation of the turbochargers. It is not uncommon for these lines to harden over time from under-hood head and eventually crack open or loosen completely. It only takes one loose line to "throw a wrench" in the entire turbo control system. The most common symptom of such a malfunction is erratic turbo performance. Often the secondary turbo will fail to produce normal boost pressures. A more catastrophic failure occurs when the boost/vacuum signal to the fuel pressure regulator pops off. When this happens, fuel pressure doesn't rise when driven under boost. As a result, you guessed it, motor failure. All these problems are avoidable with a few hours a labor and a big bag of tie wraps. This modification, however, is best left to the professionals as it requires disassembly of the intake manifold and associated components. As most third generation RX-7 owners will attest to, there is another performance quirk associated with their cars. Under cold operations, most owners complain of a 3000 rpm hesitation. Varying in intensity from car to car, it could range from a mild "hiccup" to a serious buck until the car reaches normal operating temperatures. To ease this electrical system related oddity, Mostly Mazda installed a hefty grounding strip from the engine block to the chassis. Taking all these quirks into consideration, it is easy to understand why the third generation RX-7s earned a reputation for poor reliability and quirky performance. Improperly trained dealership mechanics were given the unfair responsibility of working on a car far more sophisticated than the previous Mazda vehicle. This often led to more problems and hefty repair orders. It has taken a while for the RX-7 to become a viable daily driver. During the early years of its production, when knowledge was a scarce commodity, most third gens spent more time at the dealership than on the road. It has been semi-seriously suggested that people pass a test before being allowed to own one of these cars. Another modification is the installation of necessary instrumentation. The two most critical, but unchecked, areas in the RX-7 are boost pressure and fuel delivery. A problem with either can lead to serious engine damage. Mostly Mazda installed a boost and fuel pressure gauge from Auto Meter's attractive "Ultra-Lite" line-up. These two inch gauges were nicely fitted in Auto Meter's RX-7-specific dual A-pillar gauge holder. Both gauges were easy to install, as was holder. A boost signal was sourced from an unused nipple on the intake manifold (closest to the ABS electronics). Requiring the installation of a sender in the fuel line, the electric fuel pressure gauge was a little more involved. Mostly Mazda installed the small sender in the insulated fuel line (near the engine oil dipstick) with a simple "T" fitting. The wiring from the sender was passed through the firewall to a small electronic control module which we stashed in the driver's side foot-well, behind the plastic paneling near the fuse box. The wires from the control module were routed to the gauge, inconspicuously through the base of the A-pillar mount. Compared to mechanical fuel pressure gauges, the electric unit is far superior. Without the complication of passing a steel braided cable, filled with coolant, through the firewall, the installation is simple and maintenance-free. As with all turbocharged engines, a proper "cool down" period is necessary after spirited driving to avoid coking the turbo bearings. Although synthetic oils help, a minute or so of prolonged idling is always advised. On the race track, several minutes of idling is believed to be necessary, allowing the different engine components to recover from their various thermal expansions. This can prolong the life of the seals between the rotary housings and help prevent premature cracking of the turbo housings and exhaust manifold. Tired of siting in a hot car on a hot day, we installed a Blitz "Skeleton" turbo timer. Following the functionality-theme of our project, this helpful device sports a see-through plastic housing and provides hours of entertainment for your technically astute electrical engineering friends. Installation was a five minute job with Blitz's custom wiring harness. Once working, the turbo timer keeps the engine running after you turn off the ignition, allowing a user-programmable "cool down" period ranging from ten seconds to ten minutes. Once again, cheap insurance against an expensive turbo or engine rebuild. What The Future Holds...

For the first time in its five year life, Project RX-7 is running flawlessly (despite its on-track cooling problems.) As it is, this sports car could keep us endlessly entertained. For most people, there is little need to modify our RX-7 for enhanced performance. In the present form, it is far beyond the performance capabilities of anything this side of the $100,000 Porsche 911 Turbo. With the help and guidance of the guys at Mostly Mazda and a few top-notch aftermarket retailers, we will attempt to improve every aspect of the RX-7s already stellar prowess while minimizing daily driving compromises. We are planning quite a comprehensive "build up", ranging from a host of Mostly Mazda's power-enhancing upgrades to a ne plus ultra brake system from Cooltech. Stay tuned for the fun stuff!

Mazda RX-7: Part 3

By Shiv Pathak

Keeping Our Cool

In the last installment of Project RX-7 (SCC, Jan. '99) we focused on vital maintenance issues as well as several important reliability-related upgrades. Among them, we installed a Blitz turbo timer, and boost and fuel pressure gauges from Auto Meter. Additionally, Mostly Mazda secured the "rat's nest" of vacuum lines which lie under the intake manifold with small tie wraps. They also replaced the often ignored fuel filter that has proven to be a single point of failure for many unfortunate RX-7s.

So what's next? While increasing engine output may be tempting, it may not be the best idea at this stage in our project. Why not? As we have seen during preliminary evaluations at Thunderhill Raceway, we have already brushed upon the limits of the car's stock cooling system and brakes. According to our RX-7 guru, Brian Richards of Mostly Mazda, increasing horsepower levels may potentially excascerbate our problem.

"The more horsepower the little rotary produces, the more heat it generates. If we're already pushing the cooling system with 255 ponies, increasing output 50 to 60 percent would likely make things worse. Furthermore, if the car already suffers from severe brake fade during repeated braking from 110 mph on the long straight, it certainly couldn't handle braking from 130 mph." We agree. Increases in engine output will have to wait until we have the braking and cooling system problems under control.

Big Brakes are NOT for Wussies

According to Brian, the stock brakes prove to be exceptional performers for street use. Blessed with relatively large 11.6-inch ventilated rotors at each corner, and beautifully crafted, lightweight, aluminum four piston calipers up front, the RX-7 stops with impressive authority. Many well known automotive scribes have suggested that only a handful of high-performance exotics can match or exceed the stopping performance of the third generation RX-7. Certainly not a bad place to start.

If others find the brakes so remarkable, why do we have problems? Simply put, we are driving the snot out of the car. Much like real road racing, we are evaluating the car under severe (and prolonged) conditions. Thunderhill is no autocross. We are not hustling the car between cones for 50 seconds at a time in a parking lot. Instead we are running at or near wide open throttle on a high-speed road course for sessions lasting as long as 30 minutes. During prolonged high-speed track evaluations, heat is generated faster than it is shed. Eventually, brake components get too hot and we see fade. Unfortunately, brake fade is a fact of automotive life. Every car, from an exotic Formula One racer to a mega-buck British Touring Car, is plagued with brake fade to a certain extent. The goal in any serious brake system is to control this problem. According to Brian, there are several ways we can control brake fade. The most common and cost effective method is a simple brake pad upgrade. While Mazda has invested gratuitous sums of money in the development of the RX-7's brake pads, they are designed to meet the expectations of most "typical" consumers (low wear rates, cold friction, noiseless operation). Unfortunately, we are anything but "typical". As shameless speed freaks, we have our own set of warped expectations.

There are several high-performance brake pads available in the aftermarket. These highly specialized pads are designed to withstand the heat of heavy road racing. Furthermore, they often are less expensive than their OEM counterparts. However, this approach is not without compromise. Race pads typically don't work when cold. In fact, a few hard laps on the track are often needed to get them up to operating temperatures. Another characteristic of race pads is their tendency to shed copious amounts of dust all over the wheels and the quarter panels. Most unfortunate however, is their tendency to "chew up" rotors. Needless to say, these characteristics severely limit their "daily driving" appeal. As we have established, our goal (and challenge) in the Project RX-7 series is to dramatically improve racetrack performance, while accepting no (or very little) compromise in streetability. As an honest-to-gosh daily driver, we need race-ready brakes that will also work first thing in the morning and not squeal loud enough to compete with local air traffic. Can this be done? Let's find out. Automatically, our first upgrade to the brake system was replacing the stock rubber brake lines with inflexible stainless steel lines. Eliminating any possible expansion of the lines under hard braking was bound to result in a noticeably stiffer pedal. No such luck. With some imagination and a nice foot massage between tests, we might be able to convince ourselves of a firmer pedal. Brian was quick to point out that the stock brake lines are already incredibly stiff by most standards and little, if any, was to be gained by "upgrading" them. "If you just had to spend the $120, that's fine. It's certainly better than spending the money on a pretty faux carbon-fiber shift-knob," he remarked. Our next upgrade involved installing an appropriate brake pad. A popular streetable pad that might work fairly well on the track is the Hawk HPS (High Performance Street) pad. Priced less than the unreasonably expensive OEM pads, we owed it to ourselves to try them before we approach far more dramatic (and costly) alternatives. Once installed, we properly "bedded" them as per the manufacturer's directions. Compared to the stock pads, the Hawks provided very different braking performance. When cold, they were extraordinarily "grabby" and required much less pedal pressure. This unusually sensitive braking behavior often made threshold braking slightly more difficult. Proper heel/toe downshifts also proved to be more troublesome since slight changes in brake pedal pressure (while one "blips" the throttle with the right edge of his foot) would often make braking a bit choppy.

As we learned during our track evaluation, the Hawk's "hyper-sensitivity" to pedal pressure was only apparent on the street when the pads remain relatively cold. When the car was driven at Thunderhill Raceway, the brakes would heat up and become much more progressive and predictable. The HPS pads also held up surprisingly well (for nearly three hard laps) before any hints of fade. And fade they did. By the fourth lap, the braking zones approaching Turn 1 had to be advanced by several car-lengths. Nevertheless, they did handle the heat appreciably better than the stock pads which would have faded well before the third lap. As an added bonus, the Hawks also proved to be very gentle on the rotors. While the Hawk pads did emit more dust (and smell) than the stockers, it was well within the limits of what most enthusiasts would consider acceptable. However, it was clear that the Hawk HPS pads, while likely to be perfectly suited for autocrossing, did not meet our needs on the race track. Once again, the guys at Mostly Mazda Racing were not surprised. Another popular alternative is having two sets of rotors and pads, one for the track and one for the street. On the track, where cold stopping and noise aren't an issue, we could use Hawk's "race only" Blue pads on an extra set of dedicated rotors. Why a dedicated set of rotors? Because race-only pads contain more heat-resistant ingredients (such as Kevlar) that tend to chew up rotors. While the extra set of rotors is surprisingly affordable, and not very difficult to remove and install (especially when one is already swapping brake pads), our project goals necessitate a more elegant solution. We want to have our cake and eat it too. Is that too much to ask? To get answers to this question, we drove Project RX-7 350 miles due south towards Lawndale, Calif. to pay a visit with Cooltech Automotive LLC.

Cooltech has been designing and manufacturing state-of-the-art braking systems since 1995. Initially, Cooltech worked exclusively on high-performance European exotics, including Ferraris, Lamborghinis and Porsches. More importantly, Cooltech has also been heavily involved in IMSA race car projects that compete in various endurance races like the 24 Hours of Daytona. Luckily for the rest of us, soon after being acquired by Advanced Engine Management (AEM) in 1998, Cooltech entered the ever-growing import aftermarket. Using components from Brembo, as well as its proprietary products, Cooltech is quickly becoming a popular name with road racing enthusiasts. I spoke with the president of Cooltech, Jeff Hays, about the importance of braking performance as well as his unique approach to developing braking systems.

The Physics of Braking

Jeff is a quiet, understated man who truly appreciates good brakes. As a road racer with 12 years of experience, he knows that a superior braking system will provide a tremendous advantage over the competition. "On the track, cars are too evenly matched in horsepower to be able to accomplish a clean pass in the straights. Instead, most successful passes occur in the heavy braking zones before turns. The passing car is usually on the inside of the turn and is able to go deeper before braking. If he can slow down enough, stay on the track, and drive a good line through the turn and pull off a fast exit, he will get in front. While it is easier said than done, braking performance is crucial to winning races." We couldn't have said it better ourselves.

"So Jeff," I asked, "Can we have a no-compromise braking system designed for road racing that is also truly usable on the street?" Without hesitation and with a proud, mischievous grin, he replied, "Definitely. Let's get the car on stands, look at the stock brakes, take some measurements and see how obsessive we can be about an upgrade." Who are we to argue with that kind of attitude? Within minutes, Hays and his crew were scrutinizing the stock brakes on our RX-7. Immediately, Hays was impressed with Mazda's work. From the factory, the RX-7 uses nicely machined, lightweight aluminum calipers instead of heavy iron units typically found in many far more expensive performance cars. The 11.6x0.85-inch iron rotors are also quite good. For a car that weighs less than 2,800 lbs, the swept area the rotors and pads provide is impressive by OEM standards. Nevertheless, Hays assures me that there is plenty of room for improvement.

Before we start on our car, we should investigate the physics behind braking. Brakes are relatively simple devices which convert kinetic energy into heat. As the pads apply pressure on a moving rotor, heat is transferred into the rotor as well as into the pads. As the act of braking continues, heat will accumulate in these various components. If heat is transferred to the braking system faster than it is shed into the surrounding air, something will eventually fail. According to Hays, there are two types of brake failure often experienced on the race track. One type, as we encountered firsthand, is caused by brake pads which can eventually overheat. No problem, we did just fine with race pads, right? Not quite. While our quick and easy solution was effective, it only works up to a certain point. While the race pads will thrive on these extremely high temperatures, the other braking components are not as tolerant. The laws of physics dictate that the iron rotors can only contain a finite amount of heat. Once they have reached their maximum heat capacity (known as "heat soak"), heat will travel up the system and eventually boil the brake fluid. Once brake fluid starts to boil, all the pressure your foot places upon the brake pedal goes into crushing the tiny bubbles in the fluid, rather than squeezing the pads against the rotors. As an unfortunate result, the brake pedal slams against the floorboard, the owner screams colorful profanities, the vehicle plows off the track, and the structural integrity of its fenders are tragically compromised. OK, so brake pads can only take us so far. Hays, as always, has an answer. "The next logical upgrade after a simple brake pad swap is installing a larger rotor. Since bigger rotors are heavier, they are able to store more energy before becoming heat soaked. This will always reduce brake fade. Furthermore, large rotors offer far more overall surface area and are able to shed heat faster. Monstrous rotors also provide a distinct mechanical advantage during braking. Clamping down on the edge of a 13-inch rotor is far more effective than doing so on a 9-inch rotor. To ensure proper fit, larger calipers are almost always necessary when dramatically increasing the diameter of rotors." However, as Hays is quick to point out, installing larger rotors does have its drawbacks. Unfortunately, iron is not light. In fact, each of the RX-7's 11.6-inch rotors weighs nearly 15 lbs. Now, let's say we wanted to mount a set of extra beefy, 12.7-inch rotors typically found on perhaps the best braking production car in the world, the Porsche 911 Turbo.

While the bigger rotors would be able to stop the car in a shorter distance and be more able to withstand the rigors of the race track, they also weigh a whopping 21 lbs each. An extra 6 lbs per rotor does not seem like a big deal at first glance. However, it is important to realize that rotors (and wheels, tires and hubs) are rotating mass, so not only do we have to deal with accelerating them in a straight line, we also have to accelerate their rotational speed. In the case of round objects such as rotors, rotational inertia increases with the square of the radius. In other words, mass furthest from the center of rotation (in this case, the wheel hub) has a far greater inertial effect than mass close to the center of rotation. For big, heavy rotors that evenly spread their mass from the hub to almost the inner edges of the wheel rim, 6 extra lbs, according to Hays, is approximately equivalent to a 24 lb of static mass. Multiply again by four (for each corner of the car), and you are looking at a 96 lb increase in effective weight. For a car that Mazda went to nearly ridiculous lengths to minimize weight; adding nearly 100 lbs would certainly be a pity. Furthermore, this extra mass is un-sprung, meaning that it moves up and down with irregularities of the road surface. As all automotive engineers know, increasing un-sprung weight greatly compromises the suspension's ability to do its job. So how do we improve braking performance without sacrificing handling, ride quality, and un-sprung weight?

Fortunately for us, Cooltech has a very unique solution. Instead of using iron rotors for its top-of-the-line braking systems, it uses a remarkable material known as Metal Matrix Composite, or MMC for short. According to Hays, MMC rotors (Cool Rotors) provide several advantages compared to traditional rotors. Reduction of Rotating and Un-Sprung Weight MMC rotors are roughly one-third the weight of traditional gray iron rotors. As a direct result, handling, ride quality and even acceleration performance is improved. "Another popular alternative is having two sets of rotors and pads, one for the track and one for the street"

• Increased Rotor Life

Although exceptionally light, the ceramic composite nature of its construction make MMC far stronger and more wear resistant than iron. According to Cooltech, MMC rotors will easily last the life of the car under normal use and will never have to be "turned" (machined on a lathe). We understand they are less prone to crack or warp like an iron rotor when subjected to sudden changes of extreme temperatures.

• Increased Cooling

Depending on operating temperatures, the thermal conductivity of MMC is up to five times greater than iron. This means that MMC rotors are able to shed heat quickly and be more resistant to brake fade. Also, since the rotors operate in cool temperatures (hence the name Cool Rotors), brake pads last significantly longer. More impressively, they function perfectly well first thing in the morning when they are bone cold. MMC is still forced to abide by the laws of physics. Due to its low mass, it is not able to store as much heat as heavy iron rotors. However, its low mass does allow exceptionally large rotors which, in turn, offer more surface area to dissipate heat into the surrounding air. Coupled with the dramatically improved thermal conductivity, MMC rotors rarely experience full heat soak. So MMC rotors offer enhanced braking, better cooling, vastly improved durability, and serious weight advantages. What's the catch? Cost. MMC is expensive to machine and manufacture. As a result, Cool Rotors demand a 15 to 20 percent price premium over iron rotors. Not an unreasonable expense, of course, considering the inherent benefits provided by MMC. In fact, Chrysler uses MMC rotors with its Prowler hot-rod as does as Lotus for its high-performance, ultra-lightweight Elise sports car.

Hays measured the RX-7's big 17-inch Volk Racing wheels and determined that he could fit an enormous 14x1.15-inch rotor behind it with no interference problems. Fourteen inch? I was a bit skeptical but I kept my mouth shut. The rest of the guys at Cooltech were busy machining adapter hats and brackets out of aluminum. Hours later, once machined to precise tolerances and anodized black, the exquisite aluminum hat was bolted to the center of the rotor and test fitted on the front hubs. Fit like a glove. Since the cool rotors are crossed drilled (well, actually the holes are cast in) and impervious to warping or cracking, the stock metal splash shield behind the rotor was deemed unnecessary and removed to maximize cooling, and to shave off a little weight. Speaking of weight, the unreasonably large front rotor assembly weighed in at a mere 7.65 lbs--almost half the weight of the toyish-looking stock rotors.

In parallel, another kind gentleman at Cooltech was busy carefully machining aluminum brackets for the new Brembo four-piston caliper (that can be found behind the rear wheels of a Porsche 911 Twin Turbo). The large aluminum Brembo caliper (with bracket) weighed in at 9.45 lbs (compared to 6.20 lbs for its stock counterpart). Once the rotors were fitted and the new adapter brackets were secured to the shiny red calipers, the assembly was simply bolted to the stock hubs. Hays gracefully slid a fresh pair of Cooltech's own special proprietary brake pads (known as Cool Pads, of course) in each caliper. After quickly bleeding the system and checking for leaks, the front brakes were finally done. We eagerly mounted the wheels. Perfect fit. Hays, although relieved, was not surprised. I, on the other hand, was emotionally moved. With fist clenched, I stood in a testosterone-induced frenzy, silently appreciating the vision of magnificence which stood before me. My prolonged moment of passion was interrupted by a polite, soft-spoken suggestion that I take it for a gentle test drive. Without hesitation, Hays and I bounded into the car and headed to the street. "Go easy on them at first, and don't be surprised if the brakes initially produce some mild smoke for the first drive," Hays warned, "That's just the pads burning off some topical resin and oils." Gentle I was and smoke they did. Although I had to refrain myself from bonzai, no-holds-barred threshold braking for a few days, I immediately felt a difference in pedal feel. Offering almost no pedal travel and requiring high pedal efforts, the braking felt much like a real, honest race car. Very nice. So nice, in fact, that we decided to leave the rear brake upgrade for another project installment. For now, we will evaluate the effects of upgrading only the front brakes (which most available brake upgrade kits are designed to do anyway).

Cooling the Cooling System

Unfortunately, we still can't flog the car on the racetrack until we address the other major problem we have been experiencing--overheating. While usually adequate for normal driving, the RX-7's cooling system is inadequate for prolonged road racing. Brian Richards reports that many of his customers have had good experiences with the radiator upgrade he offers (a Mazda Competition unit). However, there have been a few complaints about its difficulty of installation. Apparently, minor cutting and trimming of the radiator brackets are involved. To learn more about this upgrade, we went straight to the manufacturer, Anthony Woodford Racing in Vista, Calif. (Before you start trying to track them down, note that all the AWR parts on our project car are available through Mostly Mazda/M2 Performance.)

Anthony Woodford has been responsible for many successful projects with Mazda Motorsports, including a rotary engine conversion for Formula Atlantic race cars as well as a Mazda Protege road race package for SCCA racing. In fact, the Mazda rotary-powered Formula Atlantic car recently won the '98 Southern Pacific Division Championships, while a Protege ES came first in its class in the Northern Pacific Divisional Championship. That same Protege also won the '98 SCCA Runoffs in Mid-Ohio. AWR has also been involved in Protomotive Racing's Mazda Miatas which have been competing in the Speedvision Cup series. For nearly four years, AWR has been working closely with Mazda Competition parts, developing and manufacturing everything from radiator upgrades to brake cooling ducts (which we already have our greedy eyes on).

His third generation RX-7 radiator upgrade is a beautiful piece of work. Unlike the stock radiator which has plastic end tanks, AWR's replacement is all-aluminum. Besides having roughly 50 percent more capacity (by using two rows of fins instead of one), it also incorporates a fin design that offers improved heat dissipation. To keep this fair, we re-used the very same coolant for the new radiator. We did, however, need to compensate for the extra capacity with a 50/50 mix of water and coolant.

Was there any fitting involved in the installation after all? Yes, some fitting was definitely required. However, Woodford has documented every single necessary snip and cut, and every new batch will incorporate these changes. The installation procedure described in Mazda's workshop manual (which all RX-7 owners should have) will finally also apply to Mazda Competition's radiator upgrade. Unfortunately, the scope of this project prohibits us from offering in-depth installation instructions. You should refer to the workshop manual for step-by-step documentation.

While the car was on jack stands, Woodford commented on the stock anti-roll bar mounts. Although, we have experienced no noticeable problems so far, Woodford has seen the stock mounts crack and break under hard driving conditions (on the racetrack). An examination of the mounts revealed surprisingly flimsy construction. The solution: A strengthened anti-roll bar mount. Of course, AWR offers many suspension upgrades, including the reinforced mount made from 4130 chrome-moly steel. Installation took a few minutes once the bars were unbolted and dropped. By late afternoon, we thanked Woodford for his help and began our 350-mile migration back to Northern California. Did the upgrades make a difference? Keep reading...

Back to Thunderhill Raceway We visit this wonderful track so often, perhaps we should pitch a tent in a paddocks and live there. Thunderhill demands far more out of brakes and cooling systems than even the most aggressive street driving or autocross. During just one brief lap of the raceway's popular East Loop, the RX-7 was forced to threshold brake from 110 mph (at the end of the long straight) to approximately 40 mph, then accelerate under wide-open throttle back up to nearly 100 mph just before threshold braking for the hairpin at Turn 2. Turn 5 (the "Cyclone") was another heavy braking zone that brought speeds down to almost a crawl before turning sharp left and descending down an off-camber, left-hander. Turn 7 was another heavy braking zone just before the sharp 20 mph left-hand hairpin leading toward the long straight. One lap of the track with an experienced driver will, without a doubt, make anyone appreciate the importance of serious brakes and a good cooling system. So how did Project RX-7's brakes handle the heat? Beautifully. With a firm pedal and almost no travel, Cooltech's upgrade is quite a revelation. Did I mention the pedal is firm? The brakes provide alarming levels of decellerative force time and time again. Passengers will complain of shoulder belts digging into their chests. Driver's will get a God complex once they develop the confidence to push the system to its limits. Cooltech's research and racetrack experiences paid off in spades. After a full session of hard driving (15 laps), we experienced no brake failures and only minor fade which only occurred toward the end of the session. By comparison, the stock brakes completely faded within two laps, while the stock brakes using Hawk HPS pads lasted roughly four laps before fade became an issue.

Heel/toe footwork was far easier since the brake pedal refused to "mush" to the floor during hard braking. In fact, under all ranges of leg effort, the pedal would only sink 1-inch before hitting a "brick wall." After that, braking could easily be modulated with changes in pedal pressure, not pedal travel. Those who have driven real race cars will certainly appreciate the brake feel. With these wonderful characteristics, threshold braking without engaging the ABS system takes very little mental effort. After a few laps of getting used to the braking characteristics, it becomes completely natural--almost telepathic.

The combination of the lighter brakes and the upgraded front anti-roll bar mounts improved handling dramatically. The differences were not only subjective. In some respects, the changes were truly obvious. Turn-in response was improved and steady-state cornering became more confidence inspiring. Body control improved greatly during back-and-forth slalom-like maneuvers. The car felt more tight, refined, and responsive. To say we liked the changes would be a gross understatement. We could not find one problem with the performance improvements. Except maybe the faster response of the steering with mild inputs. While this trait may require a bit more concentration on the driver's part, we do not consider it a compromise--in fact, we like it that way. Brain fade will not be tolerated.

If you haven't guessed by now, the radiator worked flawlessly. At no time did the temperature creep above the normal position of slightly below the half-way point. In fact, even after a full session of non-stop, full-throttle driving, we noticed absolutely no signs of the engine running hot. We will have a water temperature gauge installed by the next installment to get some real readings. So far, the results are extremely promising.

Conclusion

The first round of performance upgrades has been a resounding success. Perhaps we should stop while we're ahead. Rubbish. Let's keep climbing the magical mountain of mechanical bliss. Let's cross that vast valley of vehicular vanity. Let us pursue and pontificate performance, and all the joys it brings. Let us... aww... shucks, you get the idea. In the next installment, we will subject Project RX-7 to suspension work as well as a host of power enhancing goodies from Mostly Mazda's "M2" line of race-inspired performance upgrades. Stay tuned...

Mazda RX-7: Part 4 By Shiv Pathak

When Great Isn't Good Enough

Whoever coined the phrase "power corrupts" must have been driving an RX-7 twin-turbo. Months ago, we were praising this high-revving, rotary-powered rocket sled. While we are still mightily impressed, we can't help but wonder what some extra underhood potency would do to our beloved, yet maniacal, little Mazda. Still staying true to our initial goals of having a reliable, streetable, and durable track vehicle, we will not tolerate power at the expense of driveability or longevity. On the race track, we are still expecting a vehicle that can withstand hours and hours of gratuitous, flat-out, no-holds barred abuse--resting only to quench its unusually healthy thirst for gasoline. Since the last installment, Project RX-7 has seen over 20 hours of track testing at Thunderhill and Laguna Seca Raceway. In fact, we have even logged a few days of tire-gnarling autocross to test its impeccably quick reflexes. When it's not running at full-steam on the race track or dodging big orange cones in a parking lot, Project RX-7 assumes the unglamorous role of a Northern Californian daily-driver. It makes nightly trips to Safeway and 7-Eleven, as well as all-too-frequent commutes between Los Angeles and San Francisco. To no one's surprise, since the car was acquired six months ago, it has accumulated 15,000 miles on its snazzy, amber-glowing digital odometer (52,000 miles total). The RX-7's only downtime was at a local body shop caused by an embarrassing, fender-compromising excursion at Laguna Seca International Raceway. The bone-headed author/driver (that's me) accidentally planted two wheels off the track at turn nine. Trying to steer back on the pavement, I set the car into a high-speed, out-of-control, I-wish-I-could-wake-up-from-this-nightmare spin. Heading perilously toward the concrete wall at the inside of the turn, I stomped on the brakes, yanked the steering wheel ruthlessly, and chanted a quick prayer. Instead of smashing head-on into the unyielding barrier, the car pivoted and scraped backward along the wall. Fortunately, the damage was mainly cosmetic and failed to keep Project RX-7 from finishing the lap. (A roll bar will be installed in our next installment.) Fourteen days, several thousands of dollars, and a few cartons of Bondo later, Project RX-7 (and its humbled driver) were back on the track, as good as new, and ready to pick up where we left off. And Where Exactly Did We Leave Off?

In the previous installments, Mostly Mazda carefully secured (with small tie wraps) the proverbial "rat's nest" of vacuum lines that hide under the RX-7's intake manifold. Left to their own adhesive strategies (Read: None.), these tiny hoses tend to harden with time--eventually blowing off and crippling the turbocharger's smooth, sequential operation. Mostly Mazda also replaced the well-used, semi-clogged fuel filter with a factory-fresh unit in an effort to minimize the chances of fuel starvation. To keep an watchful eye on underhood events, we also installed boost and fuel pressure gauges from Auto Meter on the A-pillar. Another helpful gizmo was a Blitz turbo timer which we mounted on top of the steering column. Later, Anthony Woodford of AWR installed a large-capacity radiator from Mazda Competition.

This exquisite, all-aluminum radiator offers nearly 50 percent more capacity than the ineffective stock unit. Woodford also installed a set of upgraded, heavy-duty front anti-roll bar mounts, replacing the stock units that have been known to bend and eventually break under heavy loads. Finally, a remarkably sophisticated front brake upgrade from Cooltech LLC., consisting of monstrous Porsche 993 turbo front "Big Red" calipers and 14x1.25-inch metal matrix composite rotors, were installed to improve the RX-7's already exceptional stopping performance. What we are left with is a reliable, cool-running, alarmingly short-stopping, race car begging for more muscle (and perhaps a better driver as well).

Horsepower, Engine Longevity, and You

According to Brian Richards of Mostly Mazda/M2 Performance, it is possible to substantially augment engine output without sacrificing long-term durability. Drawn from his experience in the race circuit, Richards' approach to increasing the RX-7's horsepower is time-tested, as well as track-proven. Due to the fact that these unique, high-output rotary engines are capable of self-destructing with just one serious knock, Richards goes to unusual lengths to maintain a significant margin of safety.

"There are only two things that you can't do a rotary engine," states Richards. "First of all, you can't run them lean. Second, you can't run them too hot. Rotaries naturally require gratuitous volumes of fuel to keep cool and happy. Running a relatively rich air/fuel mixture under boost allows the unburned gasoline to evaporate, which in turn, cools the combustion chamber. Without this chemical intercooling system, the engine can become extremely hot and can eventually detonate itself to death."

With these issues in mind, Richards has developed a series of power-enhancing upgrade "stages," available through his aftermarket product department, M2 Performance. Each of these stages has been thoroughly stress-tested on the road as well as on the track. Instead of offering an "a la carte" selection of bolt-on upgrades that could potentially lead to a poorly integrated and unsafe-running system, Richards has put together a concrete upgrade path that ensures appropriate fuel delivery and ignition management at every step. To get baseline horsepower measurements we drove Project RX-7 to Fairfield, Calif. to pay a visit to Keith Paulsen of Superior Dyno Service. From his experience, a healthy, stock third-generation RX-7 typically generates somewhere between 215 and 225 hp at the rear wheels. Project RX-7 was no exception. Once strapped down on his portable Dynojet Model 248C dynamometer, Project RX-7 spun the heavy rollers with 218 rear-wheel hp in fourth gear--surely enough potency to squirt this sub-2800-lb lightweight around the street or track with impressive authority. With nearly 200 lb-ft of torque at only 3000 rpm, the dyno results prove the RX-7 doesn't need high engine speeds to provide alarming rates of acceleration. Interestingly, at around 4500 rpm, there is a small "hole" in the torque curve which indicates the brief dip in boost levels during the transition to the secondary turbo. Once both turbos are spinning at full clip (by approximately 5100rpm), a torque peak of 199.2 lb-ft is logged. For a car that redlines at stratospheric 8000 rpm, there doesn't seem to be much need to spin much above 6500 rpm. According to the Dynojet results, the torque curve starts immediately tapering off once peak torque is produced. From the looks of it, the RX-7 suffers from the malady common to most OEM turbo cars--massive amounts of exhaust backpressure.

With nearly 200 lb-ft of torque at only 3000 rpm, the dyno results prove the RX-7 doesn't need high engine speeds to provide alarming rates of acceleration

• More Power: M2 Performance Stage One

The first stage in Richards' series of power-enhancing upgrades consists of three components: A free-flow cat-back exhaust, a cold-air intake box, and a re-mapped ECU. After one test drive, it becomes audibly clear that Mazda designed the factory cat-back for unreasonably low noise levels and not for optimal performance. In bone-stock form, the RX-7 is a very quiet car. So silent and nondescript, in fact, that Mazda installed an audible redline "beep" to remind the driver to up-shift in case the radio or a helmet muffles the subtle sounds from the engine. In stock form, the RX-7 sounds like a finely-tuned Quisinart wrapped in a thick, woolen blanket. While the mini-wail is completely inoffensive, it is also depressingly uninspiring. With a power plant so wonderfully rev-happy and vibration-free, a more distinctive (and obvious) exhaust note would certainly be welcome.

Based on his experience with a variety of aftermarket exhaust systems, Richards chose to install a Racing Beat cat-back exhaust system in Project RX-7. Quiet at idle and drone-free under cruise conditions, this particular cat-back emits a sonorous bark under hard acceleration. It also touts polished 304 stainless steel construction, 3-inch mandrel-bent tubing, and a relatively inconspicuous (as far as aftermarket exhaust tips go) 4-inch tip (an optional 3-inch, dual-tip system is available for a more stock-like appearance). Besides its obvious visual and aural benefits, the cat-back offers a dramatic reduction in horsepower-robbing exhaust back-pressure as well as a 10 lb reduction in mass. The second component in Richards' upgrade involves removal of the stock intake system in favor of a less restrictive design. The stock intake consists of a large panel filter which draws air, via a tuned, plastic cross tube, from a front-mounted duct. This duct, which also feeds the small air-to-air intercooler, is routed from the "mouth" of the car. While the stock intake system draws cool air, it also robs much-needed airflow from the underhood-mounted intercooler. Certainly not the best performance-minded approach.

Unsatisfied with the majority of aftermarket intake systems, few of which actually draw cold air, Richards designed his own system. Expertly crafted in lightweight aluminum, the M2 Performance cold-air box houses two generously sized K&N cone filters (one for each turbo) as well as all necessary orifices for the twin blow-off valves and air pump piping. Fully shielded from the super-heated underhood air, the intake box draws a fresh, ambient air charge through a 1.5x9.75-inch opening between the radiator and an adjacent frame rail. In our particular case, our Mazda Competition radiator had to be slightly trimmed to allow air to pass though. The straight-forward installation involved unbolting and removing the stock intake assembly, dropping in the form-fitting airbox, and sliding on all the rubber hoses. Like the stock intake, the M2 cold air box effectively silences the air pump nose which, when unmuffled, sounds like a dying goose.

As many RX-7 owners have experienced firsthand, increasing intake flow and reducing exhaust backpressure can adversely affect the carefully tuned, sequential operation of the twin turbocharger system. More precisely, the secondary turbo will tend to momentarily "spike" to abnormally high boost pressures during transitional operation. According to Richards, this brief over-boost can trigger a potentially dangerous lean-run condition, which, in turn, can lead to destructive detonation. To remedy this situation, Stage 1 also tackles the electronics side of the equations by re-mapping the stock boost curves. Not only does this ECU upgrade eliminate the unwelcome boost spike, it also raises maximum high-rpm boost levels from 10 psi to nearly 12 psi. The upgrade also takes advantage of the engine's enhanced breathing ability by carefully modifying fuel and ignition maps.

Back on the Dynojet (this time at The Dyno Room at Frey Racing in Mountain View, Calif.) the RX-7 spun the rollers to a staggering 269 hp, and 236 lb-ft of torque. Improvements below 4500 rpm (on one turbo) are healthy, but when the second turbo spools up, the intake, exhaust, and ECU really start working. Interestingly, power still drops off significantly past 6500 rpm.

• M2 Performance Stage 2

The next step involves the elimination of the RX-7's troublesome "pre-cat" system. This highly-restrictive, kinked pipe connects the exhaust manifold to the main cat assembly. As its name implies, the pre-cat houses a small catalytic converter which is designed to reduce emissions during cold start. Not only does the pre-cat hinder turbo performance, it also traps heat within the engine compartment. To make matters worse, according to Richards, the pre-cat's innards tend to crumble and clog over time--the mechanical equivalent of sticking a proverbial banana in the tailpipe. This results in a dramatic loss of power and gobs of underhood heat. Replacing this hideous contraption with a 3-inch diameter, stainless-steel, mandrel-bent downpipe completely eliminates this possible point of failure while simultaneously improving engine performance and output.

Installing M2 Performance's downpipe proved to be another "plug 'n play" job. While the stock exhaust bolts can be stubborn and difficult to remove, once prepared, the downpipe literally snapped into place with minimal fuss. Using the stock exhaust manifold studs, the entire down-pipe installation procedure involved no tattered fingers, stress-induced headaches or gratuitous hair-pulling. As with the bolt-on modifications in Stage 1, the installation of the downpipe was met with appropriate ECU remapping. As Richards' predicted, the downpipe upgrade dramatically improved engine response and turbo spool up. The improvements were not only subjective. On the Dynojet the Stage 2 modifications yielded 284 hp and 252 lb-ft of torque at the wheels. At best, we gained over 68 hp vs. our stock run--not bad. Our featherweight RX-7 is fast. Very, very fast. Knock Knock. Who's There? BOOM!

Detonation, as we all know by now, can be the end of a rotary engine. Those who are used to tuning their performance cars by listening for knock, will be a sorely disappointed if they ever try to do so with an RX-7. These engines are very strong and durable if operated within their parameters. Outside these parameters, they will blow apex seals (analogous to piston rings in a reciprocating engine) before you can yell "Crap!" Although we have taken many measures to reduce the chance of detonation, we are still aware that nothing is foolproof. We know our timing, fuel and ignition maps are safe and conservative. However, there are always variables that are simply beyond our control. For example, there is always the remote chance of filling up the tank with poor quality gasoline. There is also a very real possibility of fuel starvation under hard cornering (especially with a low fuel tank). Not to mention the harmful effects of heat soak and prolonged periods of boost as often experienced on the track. Mazda addressed this need and designed the third-generation RX-7 with an electronic knock sensor that carefully listens for the early tell-tale signs of detonation and reacts by retarding ignition timing. However, for modified, high-output engines, the authority range of the knock sensor device can easily be exceeded. In other words, the knock sensor electronics are designed to provide an adequate margin of safety for a stock 255 hp, consumer-driven engine, not a 320-plus hp, race-driven engine. What is the solution?

According to Richards, the J&S Safeguard knock sensor is the best available alternative for our particular needs. Used in conjunction with the stock knock sensor, the J&S Safeguard carefully listens to the engine from a small pizeo-electric microphone which screws into the rear rotor housing. (The stock microphone screws into the front housing.) The control unit is mounted in the cabin (in our case, under the carpet in the passenger-side footwell). Offering adjustable threshold sensitivity, the Safeguard unit can be tuned to carefully listen for any preliminary signs of knock and react immediately by retarding up to 20 degrees of timing for each of the six individual rotor faces. Also available is a small, dual bar graph, LED monitor which displays amount of retard (1 light equals 2 degrees of retard), as well as a air/fuel ratio meter which reads voltage from the stock oxygen sensor.

Richards installed the Safeguard in Project RX-7 in preparation for the "Abuse-A-Thon" we have in store during our next track evaluation session. Tuning the unit takes but a few minutes. One simply adjusts the sensitivity (by turning a small knob on the control unit) until the Safeguard just barely begins to pull out ignition timing. This ensures that any atypical sound (Read: Knock.) will be met with an immediate reduction in ignition advance. For our dyno session, we ran our tests with and without the Safeguard. Since knock was not present during test, when activated, the Safeguard only retarded timing by 1-to-2 degrees. There was no appreciable reduction in wheel horsepower. While it wasn't necessary for our dyno testing, the J&S unit provided a very welcome peace of mind and perhaps the best insurance one can have against catastrophic, knock-induced, engine failure. Richards highly recommends this well-engineered system for a more modified rotary engine.

Horsepower Hype--Separating Fact from Fiction

Converting rear-wheel power figures to crank numbers is anything but straight-forward. When translating wheel figures to engine claims, some experts use fixed conversion factors. That is, if a stock 218 rear-wheel hp RX-7 is rated from the factory at 255 crank hp, it must have 17-percent driveline losses. A 284 rear-wheel hp RX-7, then, must be blessed with 332 crank hp. This popular, if somewhat optimistic, correction technique assumes driveline loss is proportionate with engine output. That is, as wheel horsepower increases, driveline loss must also increase commensurably. Some would even disregard stock quotes and apply a standard 20-percent drivetrain loss figure. Using this popular correction factor, we already have a 340-hp monster! Some would vehemently disagree. These folks would tend to use a fixed number to represent driveline loss. In this case, they would believe that all RX-7s are faced with a driveline loss of 37 hp. (255 minus 218). Using this correction method, Project RX-7 produces a more conservative 321 ponies at the crank. All three techniques, (as well as other far more [Ahem.] optimistic methods) have been used at one time or another.

Our friend at Superior Dyno Service, Keith Paulsen, looks at this issue from another perspective. "The first mistake people make is assuming that factory-quoted horsepower figures are accurate," Paulsen states. "Due to marketing hype and year-to-year tuning changes, it's not always accurate to derive drivetrain loss by comparing measured wheel horsepower and factory quotes."

Paulsen also believes that drivetrain losses are neither an absolute percentage nor a fixed number. Instead, he feels the crank-to-wheel relationship is far more beguiling. From his considerable experience, Paulsen suggests that low horsepower (100-200 hp) cars may suffer from as much as 15 to 20 percent of drivetrain loss at the rear wheels. For more powerful cars only 200 lb-ft by 6500 rpm. In contrast, when equipped with the remapped ECU, Project RX-7 exhibits a far more linear textbook approach to providing thrust. Although the RX-7 with the stock developed peak horsepower at the spike, it isn't what we would call usable horsepower. Its real peak of 255 wheel hp, which occurs at 6500 rpm, falls short of Project RX-7's lofty 284 wheel horsepower. More importantly, our car is far more driveable, faster, and resistant to detonation. Just to make sure that we didn't turn Project RX-7 into an environmentally unfriendly smog monster, we drove Project RX-7 to a local California-state emissions referee. With the intake, downpipe, exhaust, remapped ECU, and the main catalytic converter in place, the vehicle passed California's stringent tailpipe sniff test with flying colors. An underhood visual inspection would be another story, of course. Well, at least everything is bolt-on (and more importantly, bolt-off).

Suspension Upgrades: Making Good even Better?

Sometimes it seems middle-aged, mainstream automotive journalists who spend much of their time behind the large-diameter steering wheels of sedate family sedans and dreary SUVs forget what it is like to drive a real sports car. Perhaps their backsides are overly sensitive to a firm, well-dampened suspension. Or perhaps they forget a car with low-profile tire and only a few inches of ground clearance cannot possibly tackle pot-holes and gravel-strewn roads without protesting. Frankly, this is the only reason I can think of as to why other journalists have accused the RX-7's suspension of being too stiff. Hogwash. From the start, we've always felt that the stock suspension is a bit soft for our tastes. Apparently, Racing Beat Inc. of Anaheim, Calif. feels the same way. While we were at their headquarters a few months ago checking out their impressive facilities (which, by the way, still devote a lot of floor space to Mazda rotaries), Jim Langer showed us a glimpse of a brand new suspension system just made available for the third generation RX-7. Imported directly from RS*R in Japan, the coilover system offers stiffer spring rates (along with helper springs to keep the main springs seated under droop conditions), adjustable shock absorbers with enlarged oil reservoirs, and threaded spring perches for height adjustability. Also available through Racing Beat was a set of RS*R "Pillow Ball" upper mounts. The all-metal, disk-shaped devices employ a solid ball-and-socket joint (not a flex rubber interface) to provide a no-flex interface between the chassis and the shock absorber shaft. In effect, this upgrade removes every bit of rubber (with the exception of the bump stops) that existed in the stock suspension.

Installation was a breeze. Although the instructions were in Japanese, the easy-to-understand drawings speak for themselves. By the time of this writing, comprehensive directions in English should be included. The entire installation, from beginning to end, took only three hours. Since we were using the RS*R pillow ball mounts and not the stock upper mounts, there was no reason to disassemble the stock coilover assembly. The helper springs have a very light spring rate, and as a result, no spring compressors were necessary during the assembly and installation of the new coilover system. According to Jim Langer, the RS*R coilovers employ a 447 lb/inch spring up front and a 391 lb/inch in the back. For comparison, a stock '93 RX-7 sports 280 lb/inch and 198 lb/inch fore and aft, respectively. Up front, there is more height adjustability than anyone would need. It could be adjusted to ride low enough for the tires to scrape against fender lining or high enough to make a stock car look like an import low-rider. In the rear, however, the lowest perch setting could only lower our car approximately 1 inch. Significant drop, but not as low as some may desire. However, one can sucessfully lower the ride height by simply removing the small helper springs. Since our requirements didn't mandate a fashionably slammed, underbody-scraping low rider, we kept the rear helper springs in place, dropping Project RX-7 approximately 1 inch at each corner.

So how does it work on the street? From what we can tell so far, pretty darn well. With 16 steps of stiffness adjustment, the shock absorbers can vary from chatter-your-teeth stiff to exceptionally compliant and downright comfortable. Despite the significant increase in spring stiffness, the softest shock setting yielded a ride easily as compliant as the stock touring suspension and far less jarring than the over-dampened, "sport-tuned" factory R1 suspension. Road feel was also improved, no doubt due to the elimination of the rubber-laden upper mounts. While there would never be a reason to use the maximum shock stiffness under any conceivable circumstance, it's very easy to find intermediate settings that fit one's need. Once nicely dialed-in, the shock absorbers responded readily, swallowing violent bumps and pot-holes while resisting motion caused by steady state cornering and braking. What we're left with was the best of both worlds. A car that is undeniably comfortable under real-world conditions, yet still resists body roll and provides razor-sharp handling. From what could be garnered from an on-the-road evaluation, the car has become even more eager to change direction. In fact, it would be safe to say the car feels more tail-happy than a stock RX-7 which, by comparison, tends to push gently as cornering forces builds. The mild oversteer attitude provided by the new suspension does not come as a surprise considering the relatively stiff rear springs. It is possible, however, to tune for more understeer by increasing shock stiffness up front and reducing stiffness in the rear. Increasing air pressure a few pounds in the front tires would also help to keep the rear end in check.

However, for anything less than bonzai, no-holds barred driving, the cornering attitude at the limits of adhesion are never realized--especially in a vehicle that is capable of pulling 1.0 G on the skidpad. For autocross, which favors vehicles that sacrifice some stability for exceptional transient response, this suspension may be close to ideal. On a high-speed track, however, the uninitiated may find it a bit more than they bargained for. Either way, the RS*R system provides exceptional performance in a thoughtfully designed package. Conclusions

In the next installment of Project RX-7, we will continue to increase power output through the installation of a upgraded intercooler, a high-flow fuel pump, and a J&S Safeguard knock sensor unit. With the help of Cooltech LLC., we will attempt to upgrade Project RX-7's rear brakes while installing some very trick brake cooling ducts from Mazda Competition. A second oil cooler is also in store for our trusty rotary-powered steed. And what race car would be complete without a real roll bar? That's next as well. Beyond that, we still have to investigate possible clutch and flywheel upgrade alternatives, further suspension work, a vented hood, a strengthened powerplant frame, race seats, as well a host of other functional modifications. We are also going back to Thunderhill Raceway for some serious evaluation. Stay tuned because things are just starting to heat up.

Doom, gloom and a lot of other stuff

Mazda RX-7: Part 5 By Shiv Pathak

Now that we are deep into Project RX-7, it's only fair to offer a brief summary of what we have done so far. The first installment of our series (December, '98) offered an RX-7 buyer's guide and established the particular goals of our comprehensive build-up. In part II (January, '99), we addressed some vitally important preparation and maintenance items peculiar to the third generation RX-7, and uncovered the car's penchant for overheating on the track. In part III (April, '99), we initiated our build-up by installing a higher efficiency radiator, strengthened sway bar mounts, and a very trick metal matrix composite big brake system from Cooltech LLC. With heat management issues in check, Part IV (May, '99) took advantage of M2 Performance's well thought-out series of power-enhancing upgrades, which yielded a very safe and conservative 65 hp increase. With a grand total of 284 rear-wheel hp on tap, we tackled suspension upgrades by installing a fully adjustable coilover system from RSlR. Initially, this latest installment (Part V) was aimed at continuing to satisfy the power monger in all of us. We planned on installing, evaluating, and dyno testing M2 Performance's downpipe, intercooler upgrade and fuel pump upgrade. Unfortunately, a reckless grease monkey witha suspended driver's license decided to take Project RX-7 for a spin when we dropped the car off for a routine brake fluid flush. That spin ended with the driver's side front corner of the RX-7 planted firmly in the rear of a 7-series BMW. Oh, the horror!

Though the car's condition originally looked bleak, closer inspection revealed the damage was mainly skin deep. It appeared the driver's side front corner took the brunt of the impact, crumpling slightly. With no structural frame or suspension damage, the future of the car is certainly bright. So bright that M2 Performance has arranged to take advantage of this unfortunate situation by supplying the project with brand-new 1999 body parts from Japan. These updates included a revamped front bumper cover with improved cooling and intake ducts, a revised front air splitter, and a very functional, adjustable rear spoiler. By the time you read this story, Project RX-7 should be back on the track right where we left off. Our little disaster threw a big monkey wrench in the works, forcing us to redirect the focus of this installment elsewhere.

Where Exactly Is Elsewhere?

They say "God is in the little things." What "they" mean beats us, we just want our car back. Nonetheless, our plan is to use this brief hiatus as an opportunity to catch up on a few little, but important, things we missed along the way, as well as to provide a little sneak preview of what the future holds. As a few discerning readers have noticed, what you see in the pictures isn't always what you get in the project text. In Part III (brake upgrade), you may have noticed that the RS*R coilover system was already installed, but not reviewed until Part IV. You may also have noticed a Mazda Competition intercooler upgrade was peeking out of the hood in one picture, but up to this point, has yet to be reviewed. "Why?" you ask. In an effort to carefully and fairly evaluate certain products, we often install them and don't tell anyone (including the readers) until we have a good grasp of their strengths and weaknesses. On such item that comes to mind is our clutch upgrade. "What clutch upgrade?" you ask. Good question. Read on...

Clutchtober Fest

Clutch design is a hard science based on the fact that life is full of trade-offs and compromises. There is no "best clutch." A clutch that works well for one situation may be completely unacceptable for another. A drag-racing slipper clutch, for example, would be miserable for road racing. Accepting this unavoidable truth, we decided to test two very dissimilar clutches, each designed for very different applications.

The stock clutch, built by Daikin Clutch Corp. for Mazda, mates a pressure plate with a traditional organic disk. Typically, organic friction surfaces offer very nice, driver-friendly, chatter-free clutch engagement. The trade off, unfortunately, is they are susceptible to being overheated through excessive torque-induced slippage. As horsepower increases, so does torque. While the stock clutch has been known to handle our current power levels adequately, there is no harm in looking at alternatives before they become absolutely necessary. One such alternative is offered by Exedy Clutch Corp., the performance division of Daikin Clutch Corp. Exedy offers a unique three-puck cerametallic clutch which is designed from the ground-up to be streetable. The clutch itself is very similar to the unit used in SCC's Project Eclipse (November, '98). The idea of a three-puck design, compared to a traditional full disc, is to concentrate the clamping force into a much smaller surface area, increasing the pressure on the friction surface. As a result, the overall torque holding capacity improves drastically. The cerametallic material can also withstand intense heat far better than stock organic-based clutches. Along with the clutch, we also installed a beautifully crafted Exedy chrome-moly lightweight flywheel. Nine-lbs lighter than stock, the Exedy flywheel was used in conjunction with a Mazda OEM counterweight. The stock RX-7 flywheel has a counterweight cast into it, so most aftermarket flywheels require the use of the separate couterweight used on RX-7s with automatic transmissions. Although the chrome-moly flywheel weighs more than its aluminum counterparts, the Exedy flywheel has been cut with large holes towards the outer edge of its surface in a serious attempt to minimize rotational inertia while maintaining a desired amount of heat-absorbing mass. The end result is a flywheel which works like a normal aluminum flywheel, but is able to withstand more heat.

Results? The Exedy clutch grabbed hard and held up wonderfully on the track. It never showed any signs of slipping or weakening, even when used extremely hard. Pedal effort was on the heavy side, but certainly not unbearable. This could be the ideal clutch for the drag strip or road racing. However, street driving was far from enjoyable. On a car that spends more time on the track than on the road, this clutch makes sense. It is streetable, as Exedy claims, in the sense that you could very easily drive your car to and from the track. If you define streetable as tolerable in traffic and normal, day-to-day, life-in-the-big-city traffic situations, we'd have to disagree.

The cerametallic clutch was not appreciated by the vast majority of drivers. After three months of usage, Project RX-7 definitely sacrificed a good deal of its daily utility and driveability. It was stalled more times than a naughty horse. Under light use, the driving experience was acceptable, but once the clutch became hot (through prolonged stop-and-go traffic), things took a dramatic turn for the worse. Clutch engagement became alarmingly grabby and borderline offensive. I soon did everything in my power to avoid driving in heavy traffic. I also quickly dismissed the notion about allowing anyone else to drive the car on public roads without a serious crash course in clutch management. Of course, there are far less driveable metallic clutches on the market. Most of them simply don't work for street application despite one's best efforts. At the end of the day, the Exedy clutch didn't fit with the goals of the project, and it was removed in favor of something more biased toward street use.

In its place, M2 Performance installed a high-performance clutch from Mazda Competition. Using a stock, organic disc and a 35 percent stiffer pressure plate, the Mazda Competition clutch offered excellent driveabilty coupled with improved torque holding capacity over the stock clutch. Pedal effort, although marginally increased, was far from being objectionable. Otherwise, it felt very similar to the stock unit. Would the Mazda Competition clutch hold up as well as the Exedy unit under repeated drag strip launches and general abuse? Not a chance. However, this is a trade- off we are readily willing to accept given the way we use the car. Once again, we have found there is no such thing as a free lunch.

So what about the Exedy flywheel? Did it work well? Indeed it did. In fact, it worked exceptionally well. Throttle response was transformed from blurred to spastic. Although it took some time adjusting to the engine's new-found liveliness during heel/toe downshifting, there was no obvious driveability trade-off. Clutch engagement (with the Mazda Competition clutch) was completely agreeable with the Exedy flywheel in place. Starting from a dead stop took no unusual effort. Perhaps most impressive was the fact the flywheel looked fresh, even after three months of abuse with the Exedy cerametallic clutch, a sign of the heat-resistant nature of the chrome-moly construction.

Pedal Upgrades: Wider Is Better

Quite frankly, when it comes to driving sports cars, being tall isn't all it's cracked up to be. Sports cars, especially those from Japan, tend to be far more hospitable to shorter drivers. Taller folks often find most sport compacts have steering wheels which sit between their knobby knees. Not only does this look foolish, it also makes heel-and-toe footwork well neigh impossible.

Why so? To execute a proper heel-and-toe downshift, the right foot must be rotated counter-clockwise so that the toes press firmly against the brake pedal while the right edge of the foot simultaneously "blips" the throttle. For those over the national average height, the steering wheel in the RX-7 can act as a very effective blocking mechanism, prohibiting this necessary leg rotation. David Breslau, a Project Technician at the MIT Center for Space Research (no, seriously), has a solution to this height-induced dilemma. It's called the "Widefoot." Breslau, a fellow RX-7 owner and enthusiast, has developed an attractive, bolt-on pedal adapter that effectively shortens the gap between the brake and throttle pedals. This, in turn, reduces the amount of foot rotation necessary to whip off a quick heel-and-toe downshift. It works. "Wow, that adapter is actually functional," remarked Dave Coleman, SCC's esteemed engineering editor and staff giant. It looks darned nice, too. The Widefoot pedal is available in two sizes for the RX-7 and can be ordered through Crooked Willow Composites, LLC.

A Tire's Best Friend

Falling under the useful-stuff-we-would-never-think-of-ourselves category, we installed the remarkably helpful SmarTire system. Consisting of four small, lightweight sensors and one visor-mounted, back-lit system monitor, the SmarTire system constantly measures individual tire pressure and air temperatures, radioing low pressure and high temperature alerts. Installation is straightforward. One transmitting sensor (along with its counterweight) is fastened to each wheel with a large hose clamp. When the wheel is in motion, each self-powered sensor transmits air pressure and air temperature data to the system monitor every 30 and 60 seconds, respectively. With a battery life of nearly 60,000 miles, and accuracy of +/- 1 PSI, the system provides years of maintenance-free service.

But is it helpful? How could it not be? Since its installation several months ago, I no longer manually check my tire pressures before a long trip or a track event. If pressures are abnormal, we know that the SmarTire system will provide its audible warning. More importantly, who needs run-flat technology if you can effectively predict a slow leak before it leaves you stranded? It will also more than pay for itself with the cost of a single towing charge. Initially developed in England and offered as an option on the 1996 to '99 Lincoln Continental, SmarTire technology is now available in the aftermarket for virtually any vehicle that uses any standard radial tire. Of course, sensor installation is best done when you get new tires, as the procedure involves removing the tire from the rim.

Toyz 'n the Hood

What good is an RX-7 project if we fail to take advantage of Mazdaspeed, Mazda's very own performance specialty house. Offering a host of unique, OEM-quality go-fast parts, Mazdaspeed is a serious force in the RX-7 aftermarket. To test our theory that nobody does it better than the factory, we contacted Ben Miller of CSi, a Southern Californian importer of Mazdaspeed's performance products. We requested the attractive Fiberglas "Aero bonnet" (fancy name for a vented hood), a strengthened power plant frame (the bridge truss-like assembly that rigidly connects the transmission to the differential), and a short-throw shifter. With the car in its current state of unrest, we cannot offer a full review and pictorial of the vented hood. All we can say is the hood does an excellent job in attracting stares and, most importantly, dramatically reducing the RX-7's characteristically hellish under-hood temperatures. In fact, covering up the vents with racer's tape revealed a massive negative pressure zone used to effectively scavenge much of the hot air from under the hood. Although this is pure conjecture at this moment, not only does a vented hood make the car more resistant to overheating, it could also improve intercooler efficiency at speed. We eventually hope to take before-and-after temperature measurements to verify our hunches.

Originally used in the development of RX-7's little brother, the Miata, the power plant frame (PPF, for short) is made of high-tensile steel covered with a thick laminate of vibration-dampening plastic. The PPF effectively isolates the engine's torque loads that can often have an adverse affect on the chassis. Resisting windup better than a traditionally mounted differential, the PPF design allows smoother starts and launches while contributing to overall chassis rigidity and crashworthiness. While it sounds great in theory, it would be even better in practice.

However, as Brian Richards of M2 Performance points out, the stock PPF tends to crack during extreme situations such as violent, axle-hoppin' drag strip launches. The strengthened PPF sounded like a good bet. However, upon inspection, the unit, despite a pretty red powdercoat, looked strangely similar to the stock unit it was replacing. It was made of the same gauge steel and welded together at the same exact points. What's going on? Wasting no time and unable to speak Japanese, we referred to Mazdaspeed's product manual.

According to the literature, the strengthened PPF is constructed from a stronger steel material. With no advanced degree in metallurgy to prove otherwise, we must take their word for it and review the product based solely on its on-the-road merits. Did it make a noticeable difference with the new PPF installed? Hard to say for sure. Although I notice some changes in ride quality, the differences are very subtle. The car does indeed feel somewhat tighter over rough roads. With some more evaluation time, perhaps we can get a better idea of its merits.

One product met with unanimous and unabashed praise--Mazdaspeed's short-throw shifter. Compared to similar domestic short-throw units, the Mazdaspeed unit, as expected, looked and felt top-notch. Although the instructions were in Japanese, installation took no more than 20 minutes. Simply remove the center plastic console, unbolt the stock shifter assembly, and replace the old with the new. Once installed, the shifter, now operating with a new fulcrum point, can be rowed through the gates with small twists of the wrist, instead of longer rows of the arm. More importantly, it doesn't exhibit the notorious notchiness and balkiness that plagues most short shifter kits. Once again, leave it to the factory to get the job done right.

Conclusions

In the next installment, we will cover the installation of the 1999 Japan-spec. updates. In the near future, we will also install, review and dyno another round of M2 Performance's power-enhancing upgrades as well as a few of their brand-new, track-derived products. Of course, we will also be returning to Thunderhill Raceway to engage in some serious high speed evaluation in our never-ending quest to discover the ultimate real-world suspension set up. Stay tuned....

Finally! Back In The Saddle Of Our Rotary Powered Thoroughbred. But Is It As Good As Before?

Mazda RX-7: Part 6 By Shiv Pathak

Project RX-7 has finally returned to the land of the living--and it's back with a vengeance. Despite its share of misfortune, there is no denying our irrepressible Mazda is here for the long haul. But before we get too deeply involved in the current state of affairs, let's review some of the car's colorful history.

In Part I (December '98), we evaluated our pristine, bone stock '93 RX-7 while offering a "buyers guide" for potential owners. Then in Part II (January '99), we discussed the car's inherent shortcomings and initiated the early stages of our build-up starting with reliability-enhancing tweaks. Engine cooling and a big brake upgrade were the major topics we addressed in Part III (April '99). We delved even deeper into Project RX-7's performance envelope in Part IV (May '99), when we safely increased power output by nearly 90 rear-wheel hp. We were on a roll, but as fate would have it, we ran into a nasty obstacle in Part V (July '99), when an employee at a local franchised tire shop took the car out for a high-speed test drive and crashed into a parked car. Luckily, no one was hurt. But seeing a car as beautiful as our Project RX-7 lying lifeless, sandwiched between a BMW luxo-barge and a chain-link fence, was like witnessing the scene of a gruesome crime--almost enough to make a grown man vomit. Torn plastic and shattered glass littered the accident scene like garbage on the cinema floor after a day-long movie marathon. But enough dwelling on the past. Especially considering the fact our future was starting to look surprisingly bright.

It should come as no surprise to our loyal readers that a few months have passed since our last Project RX-7 installment. During this time, Brian Richards of M2 Performance gathered up everything we needed to update our battered '93 model's body to Japan-only '99 specifications (a full report on the '99 RX-7 was in the September '99 issue). During its hiatus, Project RX-7 has also been a temporary visitor to more than a few large, well-known auto body repair shops. Unfortunately, all of them were a bit hesitant in allowing our magazine (especially one annoyingly critical owner/writer) to document and photograph the entire repair process, from start to finish. Why? Perhaps no one wants to reveal the hammering, cutting, bludgeoning, welding, crying, etc., that goes on behind closed doors. Or maybe no one wants to be responsible for a well-known and extensively modified supercar that, after being fixed, isn't so "super" anymore. With no obliging repair shops in hand, we were forced to redirect our efforts elsewhere. Dejected, depressed and suffering from rotary withdrawal, we focused our waning attention on smaller, more personalized, auto body shops that (we hoped) wouldn't mind the challenge and risk involved in repairing a one-off magazine project car. We visited a few such shops, but none impressed us more than Kee's Auto Body of Concord, Calif.

Owned by Kee Huynh, Kee's Auto Body has been specializing in customized imports for nearly a decade. Pay a visit and you will find Huynh and his friendly employees mindfully working on any number of exquisite sport compact show cars, all of which would look right at home gracing the pages of this magazine. Fortunately for us, Huynh had no problem with repairing Project RX-7 despite our awkward omnipresence and silly photography-related requests ("Stand right there, hold this hammer, and don't move for the next ten seconds"). Clearly, he has nothing to hide. More importantly, he has patience. And after examining examples of his finished work, we are not surprised.

Project RX-7: On The Operating Table

It's rare to be witness to the internal affairs of an auto body shop. For that reason alone, we're going to shed some light on the entire process. Although it may not be exciting as chasing down Vipers at Thunderhill, the topic is newsworthy, nonetheless. The first step in repairing a wrecked car is known as the "tear down." As the name implies, this stage involves the removal of all damaged body panels and parts in an effort to get a clear picture of the full extent of the damages. In our case, once the front quarter panels and bumper cover were removed, we discovered Project RX-7 had indeed suffered what most believe to be the automotive equivalent of a death sentence: Frame damage. Fortunately, the damage was isolated to the small section of the frame in front of the driver's side strut tower. This means the critical "mid-section" of the car was still perfectly intact. With such minor and localized frame damage, the prognosis was excellent. So how do you straighten a frame? Answer: Like a prisoner on a torture rack. The car is clamped in place by its frame rails, adorned with chains, and literally pulled straight by unrelenting hydraulic machinery. As a finishing touch, once straightened, Huynh wielded a welding torch, chisel and hammer to artfully bend, reshape and strengthen a few hard-to-reach areas of the frame and radiator support. A little bit of grinding and a few shots of black spray paint were all that was needed to completely obscure any obvious clues frame damage--absolutely amazing.

Unfortunately, the Mazdaspeed carbon composite vented hood did not fair so well. Cracked in three places, scuffed on top, and splitting down the front edge, we were uncertain it could even be repaired. However, Huynh--ever the optimist--was convinced it was perfectly salvageable. Using a series of adhesives and strengthening materials, he carefully mended the hood to good-as-new condition. The only clues of repair were a few blotches of hardened maple syrup-like goo visible only on the underside of the hood.

Project RX-7: The Mazda Makeover

Now came the time to install the brand-new '99 front bumper. The good news: All the openings on the front fascia were significantly larger than before and should, theoretically at least, allow more air-flow through the radiator and oil coolers. The bad news: The presence of a sinfully ugly front license plate holder Mazda integrated into the front bumper. "Why?" you ask. Beats us. Our best guess is front license plate laws are far more strict in Japan than they are in the States. With this in mind, one could argue that Mazda's new bumper design, when garnished with the use-or-be-punished front license plate, allows more air flow through the radiator (and supposedly looks better) than a "normal" bumper equipped with a front plate mounted awkwardly by a generic bolt-on bracket assembly. Regardless, those who are blessed with a finer sense of aesthetics would feel it is a crime to desecrate the irreverent RX-7 with a front license plate.

This, however, would mean that recessed plate holder had to go. And, thanks to Huynh, that's exactly what happened. Keep in mind, this wasn't routine surgery. In fact, the process was quite involved and remarkably time-consuming. First, Huynh reinforced the inside of the bumper cover with a panel of Fiberglas--making the curved plastic more rigid and easier to slice and dice. Then, he cut away the entire recessed license plate holder portion, leaving a massive hole that begged for immediate attention. Initially, Huynh planned on removing the front section of the old bumper (which was still intact, for the most part) and using it as a direct transplant. However, upon closer inspection, he noticed the old donor bumper had a slightly different curvature that would not "line up" perfectly with the rest of the '99 nose. Undeterred, Huynh solved the problem by removing two portions of plastic off the side of the '93 bumper, artfully mating them with plastic weld and transplanting the assembly into the eagerly awaiting patient. After many bouts of plastic filling, repeated sanding, and artful curve-matching, the new-and-much-improved bumper cover was complete and, like the rest of the car, ready for its date with the sealed, dust-free, and temperature-controlled painting booth.

Watching a car getting prepped for painting is like watching a documentary on how ancient Egyptians mummified their deceased pharaohs. By the end of the process, layers upon layers of masking tape, paper, plastic wrap, and cloth were carefully shrouded upon our Mazda, exposing only the areas needed to be painted (front fenders, Mazdaspeed hood, and nose). With a steady hand, a discriminating eye, and one heck of a paint gun, Huynh painted the bare (but newly primed) surfaces. Concerned the color of the newly painted body parts wouldn't perfectly match the rest of the car's seven-year-old OEM paint, Huynh partially painted both doors, and in the process, carefully blended the old paint with the new. Once the painting process was complete, two layers of clearcoat were added, giving the car the much desired but rarely attained "wet look." With the car already glissening with brilliance and style, the last step involved a comprehensive finishing, polishing, and waxing.

A day later, Project RX-7 looked as good as new, fully adorned with a new front end, parking lights, taillights and a snazzy vented hood. All complete and ready for the road, we paid a visit to William Chang at C2 Automotive Inc. for an unusually accurate four-wheel alignment. Within an hour, Project RX-7 was back to its old self and original specifications.

Without A Hitch? We Think Not.

Although we were hoping all our diligent restoration efforts would be rewarded with a viceless outcome and a complete absence of teething pains, this wasn't exactly the case. The first glitch we encountered was the '99 front bumper reinforcement that had to be trimmed to fit flush underneath our modified bumper cover. Second, the stock plastic under tray/splash guard had to be re-routed slightly to fit with the new nose piece. The new twin bulb '99 parking lights also presented us with a slight inconvenience. We discovered the electrical connector didn't match up, forcing us to cut, rewire and install a set of old-style connectors. Cooling and airflow management issues also abound. First of all, the stock oil cooler ducts didn't come close to mating with the new bumper's much larger cooling intakes. Mental note #1: Order '99-spec. oil cooler ducts. Also, the space behind the radiator support and the inside of the new bumper is not sealed off--allowing incoming air to flow over, not just through, the radiator and intercooler duct. Mental note #2: Get creative with plastic paneling, a razor blade, and tie wraps. Lastly, we found that Mazdaspeed's incredibly lightweight carbon composite vented hood doesn't like to stay in one place when slicing through the air at speeds greater than 60 mph. Because we first noticed this problem when we ran with the stock bumper, our current airflow situation should not be held responsible. While it's highly unlikely the hood will catastrophically detach and tumble over the car's roof, seeing 1 to 2 inches of turbulence-induced hood flex is still disconcerting. Mental note #3: Install hood pins before the next visit to the track. While these minor problems are hardly deal-breakers, they were unforeseen glitches that should be expected by anyone interested in making similar upgrades themselves. Finally.... Boost Problems!

While not related to the makeover, but still a problem nonetheless, we've been noticing a turbo transition problem that first made itself apparent nearly two months before the accident. At first, the problem started off as a mild "hiccup" that happened every so often--only under partial throttle--just as the secondary turbocharger was coming on-line. As time progressed, so did the symptoms--eventually getting to the point where the secondary turbocharger wouldn't kick in at anything less than under wide open throttle. This "all or nothing" power delivery absolutely shattered the car's once-excellent daily driveability while contributing to some hairy on-track situations that all of us would like to forget. Fortunately, with the help of Mostly Mazda and M2 Performance, the problem, which turned out to be a lazy turbo control solenoid valve, was eventually diagnosed and immediately replaced. With nearly 65,000 miles currently on the clock, it wasn't surprising that our third-generation RX-7 developed sequential turbo system problems. With such a shamelessly complicated system, possible causes could be as simple as a malfunctioning one-way check valve (which is used to pressurize or depressurize the vacuum tanks, both of which are used to actuate the turbo switchover) or as beguiling as failing electrical connectors or loose vacuum lines (remember the "rat's nest" under the intake manifold). Fortunately, earlier in our project, we secured all the vacuum lines with tie wraps--eliminating at least one possible cause for these turbo problems.

Another problem we discovered was a torn lower intake pipe. According to Richards, it is not uncommon for these stock rubber "accordian-like" pipes to weaken, collapse or rupture as these cars get older. To fix the problem altogether, Richards installed a set of polished aluminum intake pipes (one for each turbo inlet).

Things Are Heating Up

During our last dyno testing several months ago, Project RX-7 spun the Dynojet rollers with an SAE-corrected 282 hp. With only 3,000 lbs (including the driver) to motivate, Project RX-7 is one fast car. Fast enough for most and perhaps too fast for a few.

But with summer now upon us, Northern California is plagued with ambient temperatures approaching, and often exceeding, triple digits. Unfortunately, hotter air means thinner air, which translates to substantially less horsepower. Compared to those cold crisp winter nights of yestermonth, where the intake charge were as dense as the hair on Austin Powers' chest, the summer brought upon turbo outlet temps approaching 270 F. Mixed with an abundance of fuel (as dictated by our remapped fuel curves), the engine is subjected to a power-robbing overly-rich air/fuel mixture.

There is a reason, however, for the rich-running condition. According to Richards, the surplus of fuel is the only thing keeping the car running safely under these extreme conditions. Without the extra fuel's chemical cooling properties, the blistering intake temperatures could lead to detonation which would instantly fracture the diminutive rotary engine's apex seals. The root of this evil, of course, isn't Mother Nature. The real problem lies in the stock intercooler's inability to bring the sizzling hot turbo outlet temperatures (approximately 240 F) down to near ambient levels. Yet another problem associated with the OEM intercooler, especially at our higher-than-stock power levels, is an unreasonably-high peak pressure loss of 2.6 psi (which we measured during a full-throttle 12-psi run at 7000 rpm.) Such a big pressure drop across the intercooler (which we measured before and after the two rubber "elbows" going into, and coming out of, the intercooler) means the turbo is working overtime to maintain the desired manifold pressure of 12psi. Unfortunately, over-driving a turbo forces it to operate at a reduced efficiency. The end result is higher turbo outlet temperatures and a reduction in horsepower.

Cool It

Fortunately, Mazda Competition, the performace division of Mazda of America, offers an attractive "drop-in" intercooler replacement. Unlike the stock unit which has plastic end tanks and a 2.5x11.5x4.5-inch core dimensions, the Mazda Competition intercooler is all aluminum at a slightly thicker 3.0x11.5x4.5-inch. When tested, however, the upgraded intercooler only offered a marginal improvement with respect to intake temperatures and pressure losses. Surprised by our findings, we closely compared the core design of both units. We discovered the Mazda Competition intercooler, unlike the stock unit, is equipped with turbulators in the air-charge channels. While these turbulators are designed to make sure laminar air flow doesn't become a problem (turbulent flow promotes better heat exhange), they can also increase pressure drop across the core. This increase could offset the improvement afforded by its larger intercooler volume.

However, the extra core thickness brings about its share of complications as well. According to Maxium Boost by Corky Bell, the second half of the core only does one-fourth of the heat exchanging work, making it less effective. A thicker core also makes it more difficult from ambient air to pass through--reducing its efficiency even further. With these issues in mind, it is no surprise that the juggling act of intercooler design isn't as simple as it would appear on the surface. One distinct advantage the Mazda Competition intercooler has over the OEM unit is its sheer strength of construction. With no plastic end tanks to rupture or come undone (these problems are not uncommon for road racers), the all-aluminum intercooler should physically survive under the most grueling conditions. It is no surpise that these units, for this reason alone, are popular among SCCA Showroom Stock racers. But for our high-horsepower needs, this small intercooler isn't what we were looking for.

Cool It More

The next step in the charge cooling process comes in the form of two thoroughly impressive intercoolers systems, both available only through M2 Performance. The smaller of the two (measuring a whopping 3.5x12.55x11.55-inch) is the currently largest intercooler that can fit in the stock location. The larger unit, which is nearly 6 inches wider, requires a relocation of the battery. Due to their decidedly non-stock dimensions, both intercoolers require a dedicated air duct, associated intercooler piping and intake elbow--all of which are included in the system.

While we didn't get a chance to install and test the larger of the two intercoolers yet (wait until the next installment), the smaller unit yielded simply outstanding real-world results. First of all, measured pressure loss was only 1.1 psi. As a result, manifold pressures increased from approximately 12 psi to a rock-solid 13 psi. But the biggest surprise was how effective the intercooler was at bringing peak intake temperature down to within 22 degrees of ambient!

With the cooler air charge, the engine has become more resistant to knock. The denser charge also ameliorated the excessively rich air/fuel mixture. When strapped upon the Dynojet chassis dyno, the combination of the cooler charge and slightly higher boost levels yielded an increase of nearly 20 rear wheel hp! Very impressive for a passive upgrade that becomes even more effective on the road (with real airflow). Even during the fourth gear Dynojet pull (on a 100-degree morning), peak intake temperatures rose by only 49 F. On that same day, when the test was duplicated on the road, intake temps rose by only 30 F over ambient. Also impressive is the fact intake temps are within a few degrees of ambient temperatures during cruise conditions. The combination of a true cold air box and an incredibly efficient intercooler certainly pays off. Of course, also impressive was the RX-7's real world performance. Up to approximately 5000 rpm (when operating on the first turbo), the world doesn't seem to blur by that much quicker. Above that, however, interesting things start to happen. The "switchover" is accompanied by a gratifying wad of torque (an increase of nearly 70 hp within 300 rpm), followed by a progressive swelling of turbine-like forward thrust. Above 6500 rpm, however, we experienced some distinctive misfire, which caused a dramatic roll-off in power. Nevertheless, there is no doubt that there is more horsepower to be found (heck, we're still 2000 rpm shy of redline!). But, of course, that quest is for another day. Currently, with 301 rear wheel hp on tap by only 6000 rpm, our new-and-improved RX-7 offers awe-inspiring performance while providing grin-inducing thrills. We are also looking forward to seeing how that performance translates to the track.

Coming Up...

In the next installment, we will conduct track testing at Thunderhill Park, during which time we will continue our intercooler testing by measuring intake temperatures during more extreme, sustained boost conditions. We will also quantify the effects of our yet-to-be-tested Mazdaspeed vented hood. Also in the future, we will pursue our quest for the ultimate track and street suspension set-up. Yet another monstrous big brake upgrade is on the horizon as well. The brake setup we used never ended up in production, so we want to switch from our custom setup to something that can be duplicated more easily. Of course, more tire-shredding horsepower cannot be too far away either. Stay tuned. Lots more to come.

A Few Steps Closer to the Holy Grail

Mazda RX-7: Part 7 By Shiv Pathak

Part VII already? That's right. Nearly one year has passed since we first got our hands dirty with Mazda's extraordinary third-generation RX-7. While we've lived through both the good and the bad, we like to think we've learned something during every step of the way.

Before we continue our goal of building the ultimate streetable race car, let's summarize what has been done so far. In Part I, we evaluated our then- stock, '93 RX-7 and offered a "buyers guide" for potential owners. Then, in Part II, we addressed the car's inherent shortcomings while beginning the early stages of our comprehensive build-up. Part III covered the vitally important issue of thermal management with the installation of a high-efficiency radiator and a very trick heat dissipating, metal matrix composite brake upgrade.

In Part IV, we turned up the wick even further when we began our series of horsepower-enhancing upgrades from M2 Performance. Additionally, we also installed a few goodies from the, now defunct, Mazdaspeed. Unfortunately, in Part V, things came to a crashing halt when a local tire shop drove Project RX-7 into a parked BMW. Making lemonade out of lemons, we documented the repairs in Part VI while additionally installing a modified front frascia from the Japan-spec 1999 RX-7. Resisting the temptation to rest on our rotary-powered laurels, we upped the ante even further by installing and testing two popular intercooler upgrades. With the larger of the two intercoolers now installed under its exquisite vented hood, our Project RX-7 is stronger than ever as evident during its most recent trip to the Dynojet, when it logged a tire-scorching 301 wheel horsepower run with just under 13 lbs of boost.

When Brakes Break

There are a few things in the world more stressful for a car than having it driven by a professional rally car driver on a closed track. With four heavy braking zones situated in a short, one-mile road course which is dispatched in just under one minute, brake rotors are given almost no opportunity to cool their overheating heels. Unfortunately, the very nature of the Cooltech's MMC rotor material didn't quite match our needs. Within a few hot laps, the brakes completely faded and a rotor eventually cracked.

Why? Our best guess is the MMC material needed more airflow to make use of its extraordinary heat dissipating properties. This would explain why the brakes worked well at the larger road course such as Thunderhill and Laguna Seca. Perhaps with the use of dedicated cooling ducts, the brakes could have shed heat as quickly as it was generated, and in the process, stayed intact. Unfortunately, we'll never know for sure. But in all fairness, when operating within their temperature range, the brakes worked wonderfully. With colossal 14x1.25-inch rotors and massive Porsche "Big Red" calipers, the braking system offered a mechanical advantage untouched by most modern performance cars. Capable of engaging the ABS system at nearly 90 mph (while rolling on sticky R-compound tires!), their velocity reducing abilities were never in doubt. However, as we witnessed on the small track, they failed as soon as they reached their maximum heat capacity (which is dictated, in part, by their low mass). That's too bad. With each rotor weighing less than 8 lbs, they appealed to the mass-reducing obsessive in all of us. Unfortunately, it appears the MMC rotors' most obvious strength was, in fact, their fatal flaw. That may sound overly dramatic, but certainly not as dramatic as approaching Turn 1 at 90 mph with no brakes. 'Nuff said.

Building a Better Braking System

At 2,800 lbs, the third-generation RX-7 is exceptionally light by production car standards. Through Mazda's fanatical weight reduction program (they even shortened the spark plug wires!), the RX-7 is an alarming 700-1000 lbs lighter than its comparatively adipose competition (e.g. Toyota Supra, Nissan 300ZX, and Mitsubishi 3000GT). In fact, it's nearly 300 lbs more feathery than Acura's all-aluminum NSX. As we all know, less mass means less momentum. And less momentum means happier brakes. However, as fast as this car is on a track, it will eventually be even faster. While 300 rear wheel hp is nothing to sneeze at, just the idea of another 50 ponies makes us giggle with anticipation. This and the fact we almost always run gummy race rubber would suggest there is no such thing as too much braking capability. But where do we look?

Fortunately, Brian Richards at M2 Performance has spent the last several months developing a system that could potentially fill our big brown bag of needs. As we established early in our series, everything we install on our car must maintain a stock-like streetability while offering exceptional performance. A "streetable" brake system, for instance, must be just as reliable, noise-free, and low-maintenance as the stock braking system. Installing a rackety race caliper that is designed to be rebuilt after every track testing session is not acceptable. Understanding our needs, while designing in room for growth, Richards has developed a unique big brake upgrade that should quench our thirst for decellerative g-forces. Consisting of a road-going version of AP Racing's four-piston race caliper and a 13-inch AP Racing rotor, M2 Performance's big brake upgrade is the next logical choice for our Project RX-7.

With 25 years of racing success, AP Racing literally builds the highest quality braking components in the world. For instance, the very same rotor we are using on our Project RX-7 is also used in street course racing Champ (formerly known as Indy) Car applications. While Champ Cars are hundreds of pounds lighter than our RX-7, they are designed, from the ground up, to provide positively staggering performance numbers. Running alarmingly wide wheels which are wrapped with the gummiest slicks imaginable, and armed to the hilt with mass multiplying down-force devices, the braking loads experienced by these vehicles is beyond the realm of comprehension. Imagine approaching a hairpin turn at 180 mph, standing on the brakes, and WHHOOOMMMPHHH.... by the time it takes you to read the first few words of this sentence, you are strolling into the turn at a leisurely 45 mph. Lap after lap. No time for fade. Good God man. Designed with 48 curved veins for maximum heat dissipation and made of high-quality cast iron, the slotted rotor is heat treated, then ground to a fine tolerance, and finally pre-bedded for immediate abuse. (They are, after all, designed for Champ Cars.) The result is an unquestionably stalwart 13x1.2-inch rotor that weighs, along with its anodized aluminum hat and titanium fasteners, a surprisingly light 12.5 lbs. By comparison, the smaller 12.7x1.25-inch rotors from the Porsche 911 Turbo weigh a massive 21 lbs. Even a relatively unconvincing 11.6x0.85-inch stock rotor is heavier at 14.6 lbs. AP Racing's all-aluminum race calipers are just as over-built. Equipped with anti-rattle springs that hold the brake pads firmly in place, there should be none of the squealing and clunking typically associated with full-on race calipers. And unlike the previous brake system's top-of-the-line Brembo "Big Red" calipers, AP's version has a completely recessed dust seals which tend last longer than their bellows-type counterparts (since they do not come in contact with the backside of the hot brake pad).

Like the Brembo calipers, the AP unit also uses differential bore pistons which are designed to reduce the effects of taper wear (when the leading edge of the pad wears faster than the trailing edge.) The first brake pad we will evaluate with the new brake system is the Hawk HPS pad. Designed as a high-performance street pad, the HPS is the most conservative pad we will likely evaluate. As time goes by, we will work our way upward, experimenting with pads of increased fade resistance. With some luck, we'll eventually find a performance pad which fulfills our wildest, fade-free, trail-braking fantasies while still working acceptably when cold. Enough of theory. How does it work on the track? Like usual, we took the car back to Thunderhill Raceway to find out.

Track Evaluation

It's 10:30 a.m. in Willows, Calif. when I check my brake fluid, confirm my tire pressures (32psi cold according to the ever-entertaining SmarTire system) and head off to pre-grid. By 10:35 a.m., I'm on the track. I begin my warm-up lap, remembering to stay completely off the brakes. Tire pressures are slowly rising and coolant temperatures reach a steady 180 degrees F. after three-quarters of a lap. The car is warm, but the brakes are stone cold.

Minutes later and I'm slowly exiting Turn 8 in second gear, gradually laying on the throttle. I short-shift to third gear. Back to even throttle. I exit 8A at 3000 rpm and plant my right foot to the floor. Boost gauge needle immediately jumps to an indicated 13 psi. Exhaust note deepens. The rate of acceleration begins to swell. A cacophony of hissing noises fills the cabin, piercing my helmet. At 4800 rpm, exhaust notes drop an octave and I now hear whooshing. I feel like a stone that has been launched from a slingshot. Heading towards the far end of the long and narrow front straight, I grab fourth gear as the scenery begins to blur. 5500 rpm comes and goes. I look at the speedometer and see 100 mph and rising quickly. Against every primal instinct of self-preservation, I keep the throttle floored. All in the name of good journalism, I remind myself. The cone chicane at the end of the straight is looming closer and closer. I try to remember some old kinetic energy equations from high school and fail miserably. Cones are getting big. Real big cones ahead. I begin to count to myself. Three...110 mph. Two....115 mph. One....120 mph. Hit the brake. Now. I'm going to hit the cones. Now. [STOMP!!!] WHOOOOOOOOMMMMMMPH... The car comes to a complete stop. Blood rushes back to my body--away from my palpitating extremities. The chicane stands before me. Four car-lengths before me. Damn, Champ Car brakes are nice.

With brake pads that were so frightfully effective when cold, I expected a fade problem during prolonged hot lapping. After all, brake fade is a fact of life. It happens with any and every braking system. Deal with it. But to my surprise, fade only became an issue after four or five laps of heavier-than-normal braking. In fact, I repeatedly found myself expecting too little and braking too early. Pretty remarkable for Hawk's softest Ferro Carbon street pad. But still, it would be best to use a more aggressive pad for our purposes. Fortunately, with several pad models to choice from, all fitting our AP caliper, we should have little trouble finding our pad of choice in an upcoming installment. Subjectively, the new braking system is unreproachable. Pedal feel is easily superior to that of the Cooltech system--firmer with less travel. It offers incredible feedback as well. When pressed hard, one can actually feel (through the pedal) the slotted rotors sliding against the pads. If that isn't a testament to the caliper's outstanding rigidity, we don't know what is. Also readily apparent is the fact the caliper pistons are sized correctly, making the system perfectly compatible with the stock master cylinder and brake proportioning.

The previous big brake system, on the other hand, tended to use the front brakes harder than the rears, forcing the ABS to act as an electronic proportioning device. The M2 Performance brake upgrade fits like a glove, looks like a winner, delivers all the goods, works like a charm, and whatever cliche of unabashed praise we can think of if given enough time.

Suspension Revisions

As discussed earlier in this series, it isn't unusual for us to install and evaluate a product for several months before offering one word of editorial print. Sometimes it's a matter of scheduling. Other times it's because the necessary photographs were misplaced. However on some occasions, we actually hold off judgment for more professional reasons. And such an occasion is now. Three months ago, we removed the RS*R coilover system in an effort to install something that would come closer to meeting our needs. While nothing was intrinsically wrong with the RS*R set-up, we did find it lacked the overall balance we were looking for. As we mentioned in Part IV, the car tended toward oversteer, making it difficult to get the power to the ground while exiting a turn. That, coupled with a tendency to wag its tail during high-speed lift throttle doesn't quite meet our goal of building a fast, safe, and enjoyable track car. In its place we experimented with M2 Performance's height adjustable coilover suspension system. Consisting of a set of eight-way, high-performance shock absorbers, threaded aluminum spring perches, and a vast selection of linear rate race springs, we hoped we could stumble upon something that would perfectly meet our needs of providing a vice-free, comfortable street ride while being able to withstand our idea of no-holds-barred track flogging. Little did we know our needs would change on a regular basis. Unlike our efforts with, say, Project Subaru Impreza, it isn't fair for us to criticize a car that, quite frankly, is better than any of us. Even in stock configuration, anyone short of a professional race car driver would be hard pressed to distinguish between the car's on-track strengths and weaknesses.

Instead, most (including us) are just overwhelmed by how damn capable it is. Hardly a good position from which to judge a car. Fortunately for us, Richards is also a professional race car driver/builder. With over a decade of Mazda RX-7 racing experience, Richards is a walking, talking treasure chest of knowledge. According to Richards, the third-generation RX-7 is a misunderstood sports car. He states, "The first thing most drivers do is mistake power-on oversteer for a general oversteer problem. Then they make changes in the car in an effort to improve the perceived imbalance.

"What they end up with is an imbalanced car that still suffers from excessive power-on oversteer. What the car really needs is the right kind of front-to-rear weight transfer. It needs to be able to squat down on its rear haunches slightly while biting into the tarmac. It's almost like stepping away from the road racing mentality and thinking along the lines of a drag racer." Richards continues, "Another problem with the stock suspension set up occurs during hard steady-state cornering. With stock soft spring rates, the car will lean over so much it comes very close to compressing its rubber bump stops. Once under power, the car squats back even more and actually starts to ride on them. This transition tends to make the car very tail-happy, especially on bumpy surfaces. Not surprisingly, direct replacement lowering springs make matters even worse." From what we learned during our months of tutorial and self-indulgent spring-swapping, Richards' comments seem to be spot-on. Clearly, the only way to improve upon the stock suspension would be to install a high spring rate, height-adjustable, coilover system. This would allow us to lower the car appreciably without the problems typically associated with lowering springs. It would also completely eliminate the troublesome bump stops which were only designed to keep the overly soft stock suspension from bottoming out under heavy load.

The system would also enable us to carefully pick and chose the spring rates which best meet our particular performance needs and driving style. As per Richards' recommendation, we also integrated a three-way adjustable front anti-roll bar into the new suspension system. The anti-roll bar comes complete with heavy-duty, adjustable end-links. The stiffer front bar allowed us to slightly reduce the spring rates up front while still keeping the rear rates relatively high. This, in turn, allowed us to improve ride quality while keeping body roll to a minimum.

The rear end of the car also got its share of attention. According to Richards, the stock rear suspension bushings were designed with a certain amount of compliance based on the gripping, accelerating, and braking performance of a stock car. Once one improves any of these abilities, the bushings allow a larger degree of compliance, which adversely affects alignment characteristics. Richards believes the best solution is to completely eliminate bushing compliance by replacing the stock trailing arms and toe links with heavy-duty racing counterparts. With essentially no give at either end, these elegant upgrades should theoretically provide more predictable handling under extreme uses. Additionally, they do a remarkable job in eliminating the all-to-common rear suspension "clunks" which tend to plague higher mileage third generation RX-7.

At the end of the day, the suspension we ended up with was nearly identical to Richards' Speedvision Grand Sports race car and just slightly softer than his all-out World Challenge race car. Considering the perfectly acceptable ride quality it provides on the less-than-perfectly smooth roads of Northern California, the new suspension systems easily meets our real-world expectations. With the shock absorbers set on a softer setting, Project RX-7 rides no rougher than a bone stock, R1 package-equipped RX-7. While pot holes and speed bumps are best negotiated at very slow speeds due to the "much higher than stock" spring rates, the overall ride is completely agreeable under almost every real-world condition we came across. While no right-minded passenger would mistake the car for a Lexus in a blind test, its firm but compliant ride is entirely streetable for most performance hunting enthusiasts.

On the track, however, is where Project RX-7 shines the brightest. "These cars are amazing," says Richards, "Compared to other production cars which need to be cut in half, tubed, and heavily modified in order to be competitive on the race circuit, the RX-7 needs nothing more than a few well thought-out bolt-ons. In stock form, the car already has almost everything it needs to be a real race car. It's got an incredibly stiff chassis, solid suspension bushings, all-aluminum A-arms, and light overall weight. Unlike the Saleen Mustang or the Comptech NSX, RX-7 race cars are surprisingly similar to their stock counterparts. What's even more incredible is the fact the Mazda is still the best handler of them all." And what a sweet handler it is. It's a strange feeling when you drive a car that, at first, seems to have unreachable performance limits. However, the real magic is felt the first time you find yourself exceeding those once unobtainable limits while experiencing no unfortunate consequences. Frankly, there is nothing tricky about driving this car hard. Of course, it's so blindingly fast and capable that smooth inputs and quick reactions are needed to keep it from taking an strangely unorthodox line through any given turn.

But, at the same time, it clearly communicates to the driver every gram of weight transfer and every bit of available tire grip. It's almost scary the kind of cornering speeds attainable when driving ineffably hard-core sports cars. Under braking, the car refuses to get squirrelly. While turning-in, the front end remains securely planted. The car tracks effortlessly and neutrally during steady-state cornering. Under power, the rear stays magnetically stuck to the asphalt as the car rockets in a smooth, controllable arc toward its quickly approaching apex. Just incredible.

On-Track Intercooler Tests

With a car that behaves so well on the track, we don't need much of a reason to conduct sessions of continuous hot lapping. In fact, we can even try to make it worthwhile. In Part VI of our series, we tested three intercoolers, the stock unit, a Mazda Competition direct replacement, and an enormous unit from ASP/M2 Performance. Our street testing revealed that, in terms of intake temperature reduction, the smaller units offered nearly identical performance, while the latter intecooler was clearly superior than the rest. With sustained hot-lapping on the track, however, our results could become even more interesting. Let's see how the intercoolers stand up to the punishment. Again, we did all intake temperature measurements with fast-reacting thermocouple/fluke meter device we plumbed just downstream of the intercooler. We tested two nearly identical cars. One car (Project RX-7) was equipped with the ASP/M2 Performance intercooler. The other car was equipped with a stock unit.

Other than intercoolers, both cars were nearly identical in every way. They were also driven by the same driver under similar track conditions. During our testing, ambient air temperature was 85 degrees F. The results were staggering. The intake temperatures in Project RX-7, despite 20 minutes of all-out race conditions, never exceeded 158 degrees F. By comparison, the car with the stock intercooler experienced intake temperatures as high as 248 degrees F. In fact, within 5 to 7 minutes of race conditions, a cool-down period was required to keep the car from overheating. On the other side of the spectrum, Project RX-7 (with the upgraded intercooler and high efficiency radiator) never began to show any signs of heat related stress. In fact, coolant temperatures remained constant at 210 degrees F--right where they were while idling in the paddock! Again, just incredible.

What's Next

In Part VIII of our series, we will continue to build the ultimate road-going RX-7. Among such hot-ticket items soon to be reviewed is a fully functional roll bar, an auxiliary oil cooler, carbon-fiber brake ducts, a trick F1-style steering wheel, and the adjustable rear wing you see in the pictures. Also in the works is yet another round of horsepower-augmenting engine upgrades. Stay tuned, there's a lot more to come.

Fast Car, Will Travel

Mazda RX-7: Part 8 By Shiv Pathak

Like most athletes, race cars must also be capable of performing at peak form in a number of different environments and conditions. And because we've done all of our racetrack evaluations at Thunderhill Park, it may be a good idea to expand our horizons a bit. With some luck--and, of course, a natural unfamiliarity of a new track--we're bound to learn something about our beloved Project RX-7.

So where do we take what is perhaps the fastest, track-ready road car we know of? Why, to the fastest road course in all of California of course! Located near Edwards Air Force base in Rosamond, Calif., Willow Springs International Raceway is an excellent complement to the more traditional Thunderhill Park. While some may argue that Thunderhill is the more technical of the two road courses, Willow Springs--with its simply frightening 120-plus mph decreasing-radius turn 9--is, by far the most intimidating. Also unique to Willow Springs is its strangely unorthodox Turn 3 through 6 sequence, a series of turns that combines off-camber, blind turns with a steep and intimidating hill that places exceptionally high demands on a car's suspension while allowing different cars to follow equally different lines. Willow Springs was Mazda's test track of choice nearly 10 years ago during the evaluation phase of the finalized third generation RX-7 "S1" prototype. During this time, the new RX-7 was pitted against the then-current reigning "King of the Track", Honda's exotic NSX. As fate would have it, a few smartly modified NSXs were ominously present during our very own Project RX-7 testing session as well. To prepare for Willow Springs, we installed a set of Performance Friction 90 carbon metallic race pads. Although they dust terribly and squeal like amplified pigs when cold, they should be able to withstand the rigours of Willow Springs Raceway better than the set of Hawk's high-performance street pad we've been using at Thunderhill.

Track Testing At Willow Springs

Those who are also following the build-up of SCC's Project Impreza (which, by the way, shares a residential garage with the RX-7) may recall most of the Subaru's track testing is done at Willow Springs. However, never once have we blurted such phrases as "Please, for the love of God, slow this thing down" or "Oh no, I'm think I'm going to vomit" about the Subaru's driving characteristics. These pleasantries were uttered several times (unfortunately, by me) during one such testing session in the RX-7.

With an extra 200 hp and infinitely better aerodynamics, the similarly sized RX-7 blitzed through the big track like a thoroughbred race car in fast-forward mode. At least that is how it felt from the passenger seat, as I rocketed into turn 8 at 140 mph, while peering through the cracks between my trembling fingers. Thankfully, I wasn't driving the car during this primitive fit of self-preservation; it was race car driver Gary Sheehan that was given duty behind the wheel. Readers may remember that Sheehan has track tested a few SCC feature cars in the past year. During that time, I've learned Sheehan is a very critical driver--readily willing to heap mounts of trash upon a car's slightest shortcoming with little or no remorse for anyone's feelings. So what were his impressions of the car? Let's ask him. SCC: The last time you drove Project RX-7 on the track, it was completely unmodified--driven right off the used car lot and directly to Thunderhill. What did you think of the stock car?

Gary Sheehan: I remember being very impressed with the power delivery and feel of the car. Corner exit required sensitive throttle application to prevent excessive wheel spin. I did feel the car was overpowered for its brakes [with generic brake pads] and at one point entering turn 10, the fade was so bad I contemplated what part of the embankment on the outside of the corner would inflict the least amount of damage. Luckily, no harm done. SCC: What were your first impressions of the modified car? How was it different? GS: From looking at it in the paddock, I did not expect it to be same car I drove at Thunderhill. It had bigger brakes, different suspension, a big rear wing, RA1 tires, yada, yada, yada. But it was only until I finally got the car out on the track that it started to hit me just how much of a change this car had gone through. The first thing I noticed during the warm up lap was the suspension. It was firm, but not harsh.

SCC: How did Project RX-7 feel when pushed harder? GS: As the speeds started to pick up, I was very impressed with the car's stability. Immediately, I felt the car was very confidence inspiring. More importantly, once the limits of the chassis were reached, it did nothing dramatic--it was very forgiving in that respect. I also liked the steering--very light and offered good tactile feedback. That, combined with quick engine response, made the car very easy to position, rotate and manage to the exit of a corner. The brakes were absolutely wonderful going deep into the high-speed braking zones of turns 1, 3 and 9. I wasn't even aware of them, which is how it should be when driving at the limit. All in all, the car felt much more at home on the race track than even a few race cars I have driven.

SCC: Did you notice any problems at all? GS: Well, I did go off the track once early in the session. The car inspires so much confidence that I started driving too fast too quickly. On only the third lap I was driving the car very hard and entering the corners a bit faster than I should have been doing with such little seat time. Big increments of speed can make for some big surprises. As I learned in turn 2, the car can exhibit slight understeer during long steady state at-the-limit cornering. At the speeds we were traveling at (90-plus mph) this changed our trajectory slightly and caused a four wheel off at the exit of corner 2. It really isn't a big deal at all. Except for the cone that was laying on the ground. Which I hit. Hard. But even off track those high speeds with the car completely off the track, it did nothing that surprised me and we were able to continue the lap with hardly a lift and maybe a tick or two on a stopwatch. But I must confess, the off was completely my fault, not something the car did. The only real problem with the car was engine temperatures that began to rise after four or five hard laps. That's too bad. I would have loved another twenty laps in the car to truly learn its capabilities and to turn in some really hot laps. But between the car running slightly hot and you whining and trembling in the passenger seat, I got the idea it was time to pit. "Why," one may ask, "does Project RX-7 begin to run hot at Willow Springs and not at Thunderhill?" The answer most likely lies in the fact the former is 2,500 feet about sea level. Like most OEM turbo cars, the RX-7's boost control system compensates for elevation changes. That is, at higher altitudes, the turbos are asked to spin harder and faster in order to make up for the lower than normal air density.

This is one reason turbochargers are sized large enough to be able to provide the extra airflow with minimal reductions in compressor efficiency when the air gets thin. However, it looks as if we used up most, if not all, of that reserve capacity during our previous quests for more horsepower. As a result, Project RX-7's hard-working turbos are simply over-exerting themselves beyond the point of reasonable compressor efficiencies. This creates heat. A lot of it. Combined with a sultry, 105-degree Fahrenheit ambient track temperature and thin air that doesn't carry away as much heat, it appears as if we were asking a bit too much from the RX-7's upgraded cooling system. One easy solution to this problem would be to reduce the boost level by carefully manipulating--either electronically or manually--the wastegate signal. Another safer, albeit far more expensive solution, would be upgrade to higher-flowing turbochargers. Perhaps we'll try one or both upgrades in the near future. But for now, we'll just accept the fact that, under these atypically extreme conditions, running a periodic cool-down lap is going to be a fact of life. Besides, even under these circumstances, Project RX-7 still managed to run rings around all the modified NSXs and Skylines that were present during our track testing sessions.

Pushing The Envelope

So here we are with a road car that offers incredibly high levels of track performance without extolling any significant compromises upon the driver when used as a daily commuter. Since, we've never been good at leaving well enough alone, let's continue our quest for maximum performance while keeping a vigilant eye on streetability. Many would argue we have taken the suspension tuning as far as we realistically can go without beginning to lose sight of our goals. Never having gotten the impression that we need a stiffer suspension on the track, we would tend to agree. While we will continue to play around with weight reduction, sway bar tuning and ride height in an effort to ameliorate the ever-so-slight understeer we experienced at Willow Springs, we are confident we have found our coilover system of choice. For now, let's focus our efforts on the rest of the car.

Building a Better Chassis

Two areas that we have already addressed in practice, but not yet covered in print, are chassis reinforcement and driver's safety. Because Project RX-7 began its life as a Touring Package model, it wasn't equipped with a factory front strut tower brace (which was available only in the aggressively dampened R1 and R2 sport packages.) Since our much-higher-than-stock spring rates place a great deal of load on the car's chassis, a strut brace seemed like a good idea. As usual, M2 Performance came to our rescue by providing us with a handsome, lightweight (3.5 lb) strut tower bar manufactured by Cusco. As we expected, the effects of the additional bracing were easily noticeable--enhancing both turn-in response and steering feedback. As an added visual bonus, the bar's steel strut tower mounts nicely matched our intercooler's blue silicon connecting hoses.

At 72 lbs, a roll bar doesn't really jibe with our weight-watchers approach to performance upgrades. Nonetheless, it is absolutely necessary in our minds. Provided by Kirk Racing Products, the heavy-duty roll bar made of beefy 2-inch tubing, could potentially keep an unfortunate accident from turning into a tragic disaster. Like most production road cars, the RX-7 wasn't designed to provide significant rollover protection. Considering the speeds at which our car negotiates most road courses and the exuberance at which it is driven (as we have seen firsthand, of course), we stand by the notion that a functional roll bar is mandatory and not optional equipment.

Installation, although a bit time-consuming, is very straight-forward and best done with the seats removed from the car. It's also a good idea to wrap towels around the sharp-edged mounting brackets to keep them from scratching paint or gouging the interior panels. Once the hefty steel hoop is pushed against the rear plastic storage bins (which will still remain perfectly accessible, by the way), all one needs to do is drill four holes in the floorboard, place the reinforcing steel blacking plate under the car and in-line with the hoop's floor mounts, and tightly secure the whole assembly with the provided nuts and bolts. Similarly, the rear bracing is mounted in the hatch's tool box cabinets (which, unfortunately can no longer be used). Voila. Rollover protection. Unlike the other modifications we have subjected our project car to, we hope we will never get the chance to test this particular product.

Wanna Go Faster? Go Light

When it came to reducing weight, Mazda engineers left little to be desired. However, they were forced to make a few concessions in the face of consumer expectations. First of all, they fitted the RX-7 with a 41 lb, conventionally sized, wet-cell battery. To make matters even worse, they mounted it on the front, driver's side corner of the car--far way from the center of gravity. Fortunately, there are several ways to approach this situation, varying from a simple battery replacement to as elaborate as a complete battery relocation.

The first option, as provided by N-Tech Engineering takes no more than 10 minutes and removes 21 lbs of mass. Appropriately called the Battery Miniaturization Kit (BMK, for short), it replaces the heavy lead acid battery cell with a slim (7x3x6-inch), maintenance-free 14.7 lb dry cell. Installation involves nothing more than removing the stock battery assembly and securing the BMK in its place on the frame rail. Rated at 280 cold cranking amps, Nick Reifner of N-Tech claims the BMK has enough juice to even power cars with upgraded stereo system.

Battery relocation, as suggested by Brian Richards of M2 Performance, is the other alternative and involves a bit more effort. However, the results, in terms of overall weight distribution and battery longevity are hard to beat. Using a larger (7x7x5.5-inch) Hawker Odyssey dry cell battery, Richards completely eliminates the stock-mounted battery assembly all together. Instead, he mounts the Hawker dry cell in the small storage bin just behind the passenger seat, drawing the extended battery cables from the fender well, into the cabin, under the carpet, and into the bins (from underneath). "That sounds like a lot of work," Richards admits, "But if you have to have weight [all 25 lbs of it], you want it close to the ground and away from the front of the car." As an added benefit, relocating the battery frees up enough underhood space for another, even more massive, air-to-air intercooler. But more on that later. Perhaps the only thing better than relocating mass where it can be put to good use is eliminating it all together. Such is the case with the RX-7's ridiculous Acoustic Wave self-amplified sub-woofer system. Shaped like a deformed anaconda, the plastic convoluted mess takes up much of the already limited rear hatch space, adding 22 lbs of dead weight in the process. A few twirls of the 10 mm sock wrench and out it goes. Did we miss the mind-numbing, headache-inducing, one-note bass boom that it provides? Not at all.

In order to quantify the changes in weight distribution the different weight manipulating modifications have made, we paid a visit to our good friends at C2 Automotive. Equipped with a state-of-the-art Intercomp Model SWJD weighing system, they tested each of the four different configurations with 160 lbs of journalist in the driver's seat. All tests were done with one-half tank of gasoline. The results, while not exactly earth-shattering, are interesting nonetheless. What the results illustrate most clearly is our driver-equipped, stock-batteried, bass-pumping RX-7 spreads its weight rather unevenly among all its tires. Not surprisingly, the right side (with a driver) is heavier than the right side. While the weight over the rear tires are nicely balanced with a differential of only 15 lbs, the front is uneven by a whopping 118 lbs! Such findings would suggest that, all other things equal, the car exhibits more understeer cornering right than it does left. Not coincidentally, the understeer race car driver Gary Sheehan complained about was only apparent on Willow Springs' turn 2 and 8-9 combination--both high-speed right handers.

As we expected, installing N-Tech's BMK helped matters noticeably. With the massive stock battery removed and replaced by a slim, lightweight dry-cell, both front-to-rear and left-to-right weight distributions improved. The weight differential over the front tires was reduced from 118 to 109 lbs. More unexpected, however, was the weight over the rear tires which evened out considerably. It appears, like a seesaw, that removing weight from the left front of the car transfers weight to the opposing right rear.

As Richards predicted, relocating a medium sized battery from the stock location to the storage bin behind the driver, does improve matters even further. Now, the weight differential over the front tires has reduced even further, from 109 to 101 lbs. But more importantly, the extra rear weight has been positioned down low, toward the center of the car. The removal of the 22 lb subwoofer improved matters as well--both the front-to-rear and left-to-right weight distributions evened out considerably. With our option-laden and roll bar-equipped Project RX-7 weighing in at a lighter-than-stock 2850 lbs (without driver)--we couldn't have asked for better results.

Intercoolers: Is Bigger Always Better?

Offering almost 50 percent more core volume than M2's Medium intercooler, the Race intercooler literally fills up the entire front end of the engine bay, requiring the installation of a polished aluminum "S" shaped elbow just upstream of the previously-installed GReddy elbow (both of which are included in the kit). The theory behind the larger intercooler's frontal area advantage is easy to understand. According to Corky Bell, in his book Maximum Boost , "In many respects, frontal area reflects the amount of ambient air that goes through the core to cool the intake charge. The greater the mass of ambient air that can get through the core, the greater the cooling capability." To calculate the airflow rate that goes through the Race IC's core at, say 60 mph, we multiply its frontal surface area by the car's forward velocity.

In this case, with a intercooler frontal surface area of 1.49 square feet and forward velocity of 5280-feet per hour (which is only 1 mph, but any speed is valid for comparison purposes), we calculate the airflow through the core to be a whopping 7867.2 cubic feet per minute. The M2 Medium intercooler, by comparison, is cooled with only 5280 cubic feet per minute. But to put things in perspective, the laughably small stock intercooler is treated to just under 1900 cubic feet per minute. If you are saying to yourself, "It can't be that simple," you would be absolutely right. The previous calculation assumes the intercooler has direct and unlimited access to ambient air. While that would be the case in a fully exposed front mounted intercooler, it does not hold true in our case when the intercooler is mounted under the hood and fed by a duct that offers a 2x11-inch view of the outside world. This makes things rather complicated, but as we've seen by the previous intercooler testing of M2's Medium intercooler, the ducted intercooler system works. In fact, using the results from our on-road intercooler testing (see part VI), we calculate intercooler efficiencies to be a remarkable 86 percent. In other words, during that particular test, the intercooler removes 86 percent of the heat generated by compression.

In our experience, it really doesn't get much better than that. For comparison, the stock unit--which is undersized and overly restrictive for our current air flow levels--measures in at a dismal 44 percent. The million dollar question is: Will the larger Race intercooler, fed by the same limited flow of ducted air, offer better real world performance? Keep in mind that the superior intercooler wouldn't just do a better job in cooling air--it would also have to offer similar or lower levels of pressure loss. Which intercooler is better then? To find out, we compared the Medium and Race intercoolers using our standard "on the road" testing method. Simply put, we recorded peak pressure loss (using a differential pressure gauge) and intake temperatures (using a fast-reacting thermocouple/fluke meter) during a variety of conditions. The results were surprising. [See the IC Comparison Test.]

During the full-throttle run through third gear, both intercoolers exhibited identical thermal efficiencies (approximately 84 percent). However, the smaller of the two offered significantly less peak pressure drop across its core. Looking at these results, it becomes clear the smaller intercooler fares better during this particular test. One reason for its short-term transient performance advantage may lie in its number of cross-flowing air channels--it has 22 while the Race intercooler has only 18. The greater number of channels, all other things held equal, could possibly account for the lower pressure drop. A simplified analogy would be trying to blow air through one plastic straw. Trying to blow that same amount of air through several straws would certainly take less effort, right? Now, in the case of the larger intercooler, not only are there fewer straws, but the straws are longer as well. Now, flowing the same amount of air becomes even more difficult, especially since those straws are filled with tiny fins designed to distrupt airflow--hence the 0.6-psi extra pressure loss and resultant lower boost pressures.

So, one may ask, "If the smaller intercooler offers the same cooling performance and lower levels of pressure loss, why would one ever consider the larger intercooler?" Good question. Perhaps the answer lies within the fundamentals of our intercooler testing methods. With this particular road test, we measure intercooler outlet and turbo outlet during a single third gear run from 3000 to 7000 rpm. This takes no longer than a few seconds with the intercooler never getting warm to the touch. While this may give a good indication of real-world intercooler performance, it leaves a little to be desired when it comes to sustained, wide-open throttle hot lapping on the track.

In fact, if we were to number crunch the results of the Medium intercooler's track testing (See Part VI), it's calculated efficiency would drop down to the 65 to 70 percent range. Of course, the stock intercooler, by comparison, would register a completely miserable 20 to 25 percent. We think these testing method-dependant differences in efficiency can partly be explained by the effects of heat soak, or in our case, the amount of heat getting trapped in the intercooler's core during prolonged periods of thermal loads. That is, the smaller (i.e. less massive) intercooler will get hotter when asked to absorb the same amount of heat.

Both these characteristics, as well as its larger internal volume, may suggest the Race intercooler could have some advantages when tested on the track. But one thing for sure, an extra 0.6 psi pressure loss is not a good thing. In fact, some would agrue that in order to offset the negative effects of just one extra pound of pressure loss, the intercooler would need to provide and additional 15 percent of efficiency--the main reason being the extra pressure loss would require that the turbos to spin harder to provide the same amount of manifold pressure. And, as we have all seen by now, this causes an increase in exhaust back-pressure which, in return, causes an increase in horsepower-robbing exhaust gas reversion. The only way to compensate for this loss of power would be to cool the air even further. Enough semi-educated pontificating--we'll leave the testing of that theory for the next installment.

Parting Shots

But before we sign off, we feel it necessary to give honorable mention to a couple of products that, quite frankly, surprised the heck out of us. For the last several months, we have gotten spoiled by driving on a set of Toyo Proxes RA1 racing rubber. For a DOT-approved tire, they provide simply staggering grip, predictable break-away characteristics and reasonably low noise.

However, being an R-compound tire, they don't exactly exhibit the wear characteristics most consumers expect from a tire. Fortunately, our well-balanced Project RX-7 has proven to be surprisingly easy on its tires. In fact, we were able to log an astounding 8,000 miles of mixed street and track driving--simply unheard of in the world of racing rubber. But, of course, all good things must come to an end. With the RA-1s currently resembling a heat-cycled, bald racing slick and the fact that northern California's rainy season is now approaching, we realize the need for a change. While we would be more than happy to get our hands on another set RA-1s and spend the next year wearing them to their cords, it was suggested we try a more conventional, longer-lasting (read: Non R-compound) subsitution. At first, the idea of sacrificing grip and response for a... [gasp]... longer-lasting street tire didn't sit well in our stomachs. How could we possibly justify a change that would surely result in compromised road-carving performance? After doing a good deal of research, we decided to go with Yokohama's new AVS Sports--partly because its unique tread design reminded us of an honest-to-God wet weather racing slick. But the biggest question on our mind was if Yokohama's flagship street tire would live up to the racy performance its looks suggest. To find out, we mounted 235/45-17s up front and 255/40-17 in the rear--the same staggered sizing used on Mazda's Japan-only '99 RX-7. Even before reading the product information provided by Yokohama, we knew there was something different about these tires. Like real race tires, there was a noticeable absense of tread squirm--something one doesn't really notice until it's gone.

What makes these tires different? A good part of the answer is in its strange tread design. The massive center block, constructed of one single piece of road-contacting rubber, is designed to resist a tire's natural tendency to deform or "wiggle" under loads. Surprisingly, the AVS Sports' unique character was not only felt under hard, at-the-limit cornering, but also in gentle lane changing and braking. And contributing to the AVS Sports' unsually strong resistance to "roll" onto its shoulder during maximum cornering loads are its unique, large lateral tread blocks and precisely shaped casing. But the AVS Sports' level of performance isn't without its trade-offs, perceived or real.

For one, like real race tires, the Sports are more prone to follow grooves and other irregularities in the road--requiring a bit more attention and correction from the driver. And secondly, one could possibly interpret the Sports' quick and decisive responses to be a sign of a less-forgiving tire. However, we would agrue the later is not the case with a car as predictable and intuitive as our Project RX-7. In our situation, it's certainly an advantage to run on tires that respond immediately, than on ones that feel slighty indecisive. Not only does this make the car ultimately faster around a track, it also complements the very nature of the RX-7--even when driven casually on the street. While their ultimate grip is as good as, if not slightly better than, the other UHP street tires on the market, it is the Sports' unique subjective "feel" that has won a place in our hearts.

Coming Up...

In addition to intercooler testing at Thunderhill, we will also resume our quest for more horsepower. And as if Project RX-7 wasn't already raced-out enough, tune in next time and take a peek at what could very well be the widest and stickiest set of Hoosier racing slicks this side of a World Challenge car. Stay tuned.

The Evolution of a Revelation

Mazda RX-7: Part 9 By Shiv Pathak It's been nearly two years and over 35,000 redline-charging miles since we acquired our 1993 RX-7 Touring Package. Other than a few minor bumps and scrapes along the way, our car continues to blaze up the local race tracks, resting only to quench its freakishly healthy thirst for Chevron's finest. With almost two years of tweaking, fiddling, testing, and flogging under our well-worn seatbelts, we feel it's about time to recapitulate of all the major work (and, of course, money) that has seeped into what has easily become the raciest project car in SCC's illustrious history. The following outline covers only the quantifiable and easily reproducible basics and ignores all the miscellaneous do-dads that have yet to be tested. Building Your Own Beast

Now 7 years old and hopelessly misunderstood, this stellar example of what a sports car should be can easily be purchased for a song. Make sure to follow the shopping guidelines offered in Part I of the project series (December, 1998). Be sure to know what you are getting into; these cars require unique care and consideration. Fortunately, once properly set up, the RX-7 rewards your efforts tenfold... and then some.

COST: $17,000 to $22,000 High Efficiency Radiator Perhaps the single, most glaring weakness of the FD3S (the internal designation for the third-generation RX-7) is its marginal engine cooling capacity. This is especially bad considering that overheating is almost guaranteed to destroy a rotary engine. This all-aluminum, drop-in radiator upgrade should be considered a mandatory upgrade for anyone who lives in a warm climate or drives on the track. Consider it cheap insurance. Well, not too cheap. And don't forget to buy the coolant expansion tank bypass kit ($49) and 1.3 bar radiator cap ($18) to go with it! COST: $617 (radiator only)

M2 Performance Stage III Engine Package Like a 500 cc shot of adrenaline, these simple, bolt-on upgrades make a quick car even quicker. Consisting of a cold air intake, large intercooler, 3-inch exhaust down-pipe, 3-inch Racing Beat cat-back exhaust and remapped ECU, this series of upgrades increased output from a meager 218 rear-wheel hp to a far more enjoyable 301 wheel hp--all without taking a toll on reliability or drivability.

COST: $3,650 J&S Safeguard Knock Sensor with Dual Monitor After overheating, detonation is the next leading cause for rotary engine death. Considering it only takes one or two pings to send the two-rotor RX-7 into 1.3333-rotor configuration, an active form of detonation sensing is a really good idea. Even with conservative performance tuning, there's always the very real possibility of filling up with a bad tank of gas and not realizing it until it is too late. Snaps, crackles and pops should be heard at the breakfast table, not while driving your rotary-powered steed.

COST: $595 Tires and Wheels Would Carl Lewis ever run a 50-yard dash in Velcro-fastened Keds? This same principal applies to the FD3S. There are several viable high-performance tires available, each with its strong and weak points. Our favorites have been the Yokohama AVS Sports and Toyo RA-1s. However, as good as street tires (even R compound ones!) have become in recent years, they are still slippery compared to real race rubber (like the Hoosier racing slicks we are currently testing). Our elegant but costly solution? Buy two sets of rims and tires--one for the track and one for the street! One hint: Go forged and go light. We are using Volk 17-inch TE37s on the street and 18-inch Forgelines on the track--both are light and as strong as hell.

COST: $2500 to $5000 per set of wheels and tires. M2 Performance Suspension Package Ah, the black art of suspension tuning. After countless hours of track testing, we ended up with the same suspension that adorns M2 Performance's World Challenge race car. Not exactly a coincidence considering even more countless hours were poured into its development as well. Included in the package are GAB Super R adjustable coilovers, upper strut plates, heavy-rate Eibach race springs, an adjustable front anti-roll bar with reinforcement mounts, strut tower brace, adjustable competition trailing arms and toe links. When set up correctly, the system performs even better than the sum of its parts. On the road, however, it can be a little stiff-riding for some tastes.

COST: $2,660 High Performance Clutch and Lightened Flywheel With an estimated 350 engine hp on tap, a beefier clutch is a necessity. Fortunately, all we needed was a higher clamping pressure plate (plus 30 percent) and another stock, organic friction disk. After spending some quality time with a "streetable" cera-metalic clutch disk, we're more convinced than ever that organic is the way to go if the car is to be driven on the street. We eventually settled on an ACT pressure plate. Somewhere in the middle of all that clutch swapping, we installed a very trick Exedy chrome-moly lightened flywheel, improving throttle response without sacrificing drivability. There are many clutch and flywheel alternatives available, each with their share of relative compromises. Take your pick.

COST: $950 and up M2 Performance Big Brake Package Consisting of four-piston AP Racing calipers and authentic 13-inch AP Racing Champ Car rotors, our big brakes proved we can have it all. By simply changing front brake pads, we get quiet, trouble-free operation on the street as well as ruthlessly consistent performance on the track. For the rear brakes, we kept stock rotors and calipers and use only Hawk Blue race pads. In either configuration, the brakes offer Porsche-humbling pedal feel, glorious initial bite, and excellent front-to-rear braking bias. We had earlier tried using Aluminum Metal Matrix Composite (MMC) rotors, but based on our experience, we're not yet confident they are viable for heavy use.

COST: $2,835 with all the necessary brake pads Kirk Racing Roll Bar Of all the things we could have skimped on, safety is not one of them.We hope the roll bar is the one upgrade we will never test. While we can't honestly say we feel any differences in chassis rigidity, we can admit to feeling a lot less stupid when we're entering Turn 9 at Willow Springs at full speed.

COST: $350 Sum Total Is dumping over $20,000 worth of performance upgrades on a quirky, rotary-powered sports car a defining act of sheer stupidity? It certainly is if you're looking for a clever financial investment. However, if your only goal is to drive a car that can ignite the fuse on the back of your primitive, endorphin-producing cerebral lobe while out-performing nearly anything on the road or race track, your hard-earned money couldn't be better spent.

Back to Business As Usual

As I sit down in front on my computer and try to compose the rest of this project installment, I realize my job becomes increasingly difficult as this series progresses. Nearly two years ago, the job was easy enough; to improve upon a third generation RX-7's strengths, ameliorate its weaknesses, while still retaining a reasonable amount of daily utility. These days, it's nearly impossible to follow that same premise. Why? Because, quite frankly, our creation out-performs just about anything we dare compare it to. And therein lies the problem with Project RX-7: Its limits are too high to probe on any public street, up any empty mountain road, or through any twisty back road. Sure, it can be driven fast enough to make your head explode, but that won't tell you anything about how the car behaves at its limits. And that is precisely what this car is all about. At this discrete point right at the top of its sizable performance envelope, Project RX-7 offers something that most other ultra-high performance cars simply can't match--forgiving speed. Not only does velocity comes so easily and so rapidly, but minor driving blunders going largely unpunished. So unique is this endearing quality that any slow-witted driving hack like myself can come across looking as if he was born with the innate ability to heel-toe downshift and confidence lift at triple-digit speeds. How the hell do we make this car any better? We're working on it. But first, let's take a couple steps back and fix a problem that have been bothering us for quite some time. Shocking Discoveries

A few readers may have noticed that we at SCC have found yet another toy to rub our pointy little heads against. It's called the Roehrig shock dyno and it tests... you guessed it, shock absorbers. While shock dyno results are relatively easy to understand (read February, 2000 "Technobabble"), applying the results to the real world takes a great deal of knowledge and experience. For that reason, we're not going to tread through any deep waters.

For now, we'll stick with basics and leave the serious suspension tuning issues for another installment. Instead, let's compare and contrast a few different shock absorber available for the FD3S. First, look at the two factory offerings. The FD3S was available with two different shock absorbers. The Touring Package came with relatively cushy shocks, while the R1 package was a buckboard-stiff kidney pounder. Looking at the Touring Package shock's dyno results (page 272), it is clear the Mazda engineers were trying to balance the scales between decent performance and pleasantly supple ride quality. Using relatively soft springs rates (280 lb/in. front and 200 lb/in. rear), the engineers felt they could get away with minimal rebound damping. The downside is the RX-7 can feel floaty at times, tending to dive, roll, and squat during evasive maneuvering.

On the other hand, compared to the stock shocks, the Bilstein shocks that came with the R1 package (page 276) offer gobs of rebound damping--especially in the front. On the road, this extra damping results in a tight, well-controlled ride. But why the disproportionate amount of front rebound damping? Perhaps this was an attempt to stiffen the front end of the car without resorting to heavier rate springs. While shock damping doesn't influence effective spring rate or overall cornering balance, it does influence the way a car responds to input--either from the driver or from the road. To the driver, the extra front rebound damping yields, among other things, improved road feel, less squat under acceleration, and improved turn-in. What front rebound doesn't yield is extra understeer or less brake dive--as one would expect from stiffer front springs. As its name implies, the Koni single-adjustable shock absorbers (see dyno on page 274) are adjustable in rebound only. And unlike other adjustables, the Konis do not have discrete settings in the form of discernible adjustment knob detents or "clicks." Instead, the adjustment knob spins smoothly from one end to the other, making it difficult to establish reference points and plot out individual damping curves.

Perhaps the most striking characteristic of the Konis is that, unless set to full, rock-hard, low-speed stiffness, they offer significantly less low-speed compression damping than either the stock or Bilstein shocks. While such low-speed shock valving yields a smooth ride, it also results in more brake dive and less immediate turn-in characteristics. On the rebound side, things look better. On the softer settings, high-speed rebound damping is as gentle as that of the stock shocks. And on the stiffer settings, high-speed rebound damping becomes greater than the stock shocks.

What does this tell us? For starters, it suggests Konis, by virtue of their still rather conservative rebound damping, are best suited for use with stock or close-to-stock spring rates. If significantly stiffer springs are used, the Konis may not offer sufficient high speed damping to prevent unwanted spring oscillations which would result in a floaty, under-damped ride. One thing abundantly clear is that you never want to run Konis with the adjuster cranked all the way to full hard. Low-speed damping in both directions goes super-stiff when the adjustment valve is completely closed, so they should never be run more than 1/8th of a turn from full stiff.

At first glance, it's obvious the GAB Super R double-adjustable shocks (see dyno on page 274), with their generous rebound damping characteristics, were designed with stiff springs in mind. This was one reason we opted for these shocks on our slightly lowered and very stiffly sprung project car. Another advantage of the GAB shocks is their nice, evenly spaced range of adjustments which makes suspension tuning less guesswork and far more intuitive. Also adding to the GAB's impeccably sporty flavor is its abundant low-speed damping, which results in razor-sharp turn-in, reduced pitch, dive and roll, as well as super-quick steering response. The downside? Check out that medium- to high-speed compression damping. Yikes. Not exactly the most suitable shock for rough road commuting, is it? The moral of our story: Although we have found the shock that works the best for us, there is no perfect shock absorber. Yet. Yet? That's right, as you read this, M2 Performance is working on an independently adjustable (for rebound and compression) ultra-high performance shock that should potentially come the closest to meeting our street and track needs. Offering extensive valve adjustability, the new shocks should be able to meet any reasonable set of expectations.

Rantings of a Sparkless Lunatic

We blamed the solenoids. We blamed the wires. We blamed the coils. We blamed the remapped ECU. We even thought about blaming the All-Mighty Himself. No matter what we replaced or at whom we pointed our grungy fingers, we just couldn't seem to clean up the high rpm misfire that made full throttle blasts to the 8000 rpm cut-off less than enjoyable. But finally, we ran into the source of the stumble: A damaged electrical connector in our ignition sub-harness. With one wire barely making contact with its terminal, the front rotor's spark plugs wouldn't spark during unusually heavy load or at high engine speeds. Not only was this the source of our top-end torque roll-off, it also explains the partial-throttle "bucking" we experienced during single-to-twin turbo transition. Of course, trying to buy an ignition sub-harness from the dealership without having to purchase the complete and very costly electrical harness is like trying to extract teeth from a digestive orifice other than the mouth.

Fortunately, famed RX-7 drag racer and proprietor of SR Motorsports, Ray Lochhead, came to the rescue, finding the object of our desires in a pile of unused parts. As they say, one person's garbage is another's treasure. But our sparky misadventures didn't end there. Several weeks and a few track testing days later, we began to notice yet another ignition quirk, this time only during secondary turbo transition. As we were preparing ourselves for yet another fantastic voyage deep into the RX-7's dense engine bay, Brian Richards of M2 Performance posed a thoughtful question, "When was the last time you changed the spark plugs?"

Good call. Once removed, our leading spark plugs showed evidence of excessive wear. Perhaps a result of our excessive track testing, eh? "A track-driven RX-7 is very hard on its spark plugs," Richards explained, "and they won't last nearly as long as many people would expect. Sometimes they'll last 15,000 miles and other times only 7,000 miles. Either way, they are the first things that should be inspected anytime misfire becomes a problem."

Since the stock plugs fail to offer the longevity we would expect from a not-easily-replacable-without-using-a-lift-or-burning-your-forearms item, we took two steps in the right (colder, that is) direction by replacing our old NGK BUR7EQP leading and trailing plugs with four nearly identical NGK BUR9EQP plugs. Why the colder plug? Well, it appears as if the stock plugs are being put through hell. The culprit? Extreme heat, of course. And the colder the plug is rated, the less heat it retains during combustion. And the less heat it stores, the less hell it goes through and the longer it lasts. But, like everything else, there is a downside to using a colder plug. Since they don't run as hot, they don't do as good a job of burning themselves clean. As a result, they are more prone to fouling during thumb-in-the-mouth, sissy-boy driving. The solution? Duh. Do you really have to ask?

Just When You Thought It Was Safe To Pick Your Favorite Intercooler

In our previous installment (November '99), we compared two high-end intercoolers, finding that the merely large "Medium" M2 intercooler actually performed better than the simply huge "Large" M2 intercooler. While the charge cooling ability between the two units were comparable, the larger intercooler suffered from a 0.6-psi greater pressure loss. And as we all know by now, pressure loss is evil.

We concluded this extra loss was most likely the result of the large intercooler having fewer (18 vs. 22) and significantly longer (17-inch vs. 11.55-inch) cross-flowing intake channels. Fewer and longer tubes, all things equal, should pose a greater airflow restriction, right? By a unanimous decision, we declared the medium intercooler the outright victor and called it a night.

Mr. Biggie is back. Fitter than ever. And ready to put some serious hurt on the reigning charge-cooling champion. Armed with a new core design and a reshaped intercooler outlet elbow, the once-humiliated heavyweight is on a mission. And that mission is clear: To cool some hot air.

Enough of the pointy-headed melodramatics. After an evening of thermocouple wielding and differential pressure gauge monitoring, it appears we have a new champion.

These results also shed some light on what we've said in the past about intercooler design. Since both intercoolers offer identical pressure loss, it would appear that the extra core length poses no significant restriction to incoming air. Instead, we can now argue that the old large IC's 0.6-psi greater pressure loss was almost completely a result of it having four fewer internal charge tubes. Another contributor to the new large IC's enhanced pressure drop performance is its slightly revised "S" tube that offers a smoother, less turbulent path for air to flow between the intercooler outlet and the GReddy intake elbow.

According to additional comparison testing, the revised "S" pipe alone was worth a 0.1-psi reduction in pressure loss! In addition to the large intercooler's much-reduced pressure drop, cooling efficiency has also been improved measurably. This fact addresses yet another notion we once entertained regarding large, stock-mounted intercoolers. That is, we had reached the point where charge cooling was being limited by the amount of airflow that passes through the intercooler duct, and not by the intercooler itself. Obviously, with these new results, we have proven ourselves wrong--once again. Next Time

Is this really the best intercooler? Are our expectations of the perfect, no-compromise shock absorber reasonable? Have we done everything there is to do to an RX-7? We'll find out in the next installment. Also in the works are other full-fledged racing modifications that should make the heart of any race enthusiast palpitate with excitement. In addition, we'll finally be able to quantify, in terms of drag and down-force, the effects of our adjustable rear wing. By then, we'll have gone through a set of Hoosier R3S03 DOT-approved racing slicks and will be able to give you the full story behind serious race rubber and how they compare to even the best street tires. Stay tuned.

Prices

• Mazda Competition Radiator.......................$617
• Expansion tank bypass and radiator cap......$67
• M2 Performance Stage III kit.....................$3,650
• J&S Safeguard.............................................$595
• ACT Clutch..................................................$420
• Exedy Flywheel...........................................$500
• 4 Volk TE37 wheels......................................$2,100
• 4 Yokohama AVS Sport Tires........................$724
• 4 Forgeline Suzuka wheels............................$2,550
• 4 Hoosier R3S03 Tires...................................$800
• M2 Suspension Package................................$2,660
• M2 Big Brake Package.................................$2,595
• Kirk Racing Roll Bar.....................................$350
• Total: .....................................................$17,628

Faster, safer, cleaner

Mazda RX-7: Part 10 By Shiv Pathak

Nearly two years ago, when we first began our RX-7 series, we set forth an upgrade guideline that we have strictly adhered to ever since. We stated that we will maximize racetrack performance while not, under any circumstance, unduly compromising the RX-7's streetability or durability. What this has meant to us is that we had to keep one foot planted firmly in the real world. A world that frowns upon unmuffled exhaust systems, squealing brakes, rock-hard suspensions, Lexan(TM) windows, and stripped, bare-bones interiors. We've been good. But now, we want to have a little extra fun. So much extra fun, in fact, that we're going to temporarily ignore our self-imposed restriction. Our reason? The need for speed, of course! Grip of the Gods

OK, the cat is out of the bag. In the last few months, we found the one modification that transformed our raceable street car into a not-so-streetable racecar. What is it? Here's a hint: They're big, fat, and stickier than a movie theater floor after a week-long Star Trek marathon. They're Hoosier R3S03s and we're bananas for them. Compared to any other brand of rubber we've tried on Project RX-7, these road racing tires demand respect. In terms of performance, they start where the Toyo RA-1s end. The designers of the R3S03s only had one goal in mind: Grip. Everything else is meaningless. Too much noise? Wear ear plugs. Too much tramlining? Keep both hands on the wheel. Ride too stiff? Stop whining and drive. This tire is all about going fast. It's about winning races. See that DOT-approval marking? Don't pay attention to it. It's not a street tire any more than a blowtorch is a cigarette lighter. The tread might as well have been painted on with an airbrush because after a few hard laps, the tires become flat-surfaced racing slicks. Serious stuff.

Obviously, Hoosiers don't really belong on the street; they belong on trailers or crammed into the back seats of race support vehicles. The track-only nature of the Hoosier's limit their appeal, but so what? There's no other upgrade that rewards so much and costs so... uh... never mind. Although our tires (245/35ZR-18 fronts and 275/35ZR-18 rears) cost an utterly reasonable $900, they offer a UTQG wear rating of only 40, meaning that they will need to be replaced every few track days. But if your first priority is speed, they are worth every penny. Trust us.

Of course, a dedicated set of racing tires demands a dedicated set of racing wheels. Wanting something very strong, lightweight, and seriously good-looking, we looked no further than Forgeline Inc. of Dayton, Ohio. Enter the Forgeline Suzukas. Weighing a tad under 20 lbs for a massive 18 x 9.5-inch rim, the gorgeous polished aluminum Sukuzas perfectly met all our requirements. Unlike many other forged wheels, the Suzukas are 100 percent forged 6061-TG aluminum, center section and all. Also unlike many other wheel manufacturers, Forgeline does not make "universal fit" wheels. Instead, each wheel is custom-made to fit a specific application. Also notable is the amount of caliper clearance. According to Forgeline, its wheels are designed to accommodate all aftermarket brake packages. Although we can't confirm that claim, we can say that our 13-inch AP Racing big brake upgrade fits fine with a lot of room to spare. To ensure that we encountered no fender clearance problems, we opted for 18 x 8.5-inch rims up front and 18 x 10-inch at the rear. Yummy.

Less Ricey. More Racey.

Take a look at the dashboard layout of any purpose-built race car. What do you see? Not too much. That's right. No fuss. No muss. Cold austerity, plain and simple. Is this because racecar drivers are grim and joyless people? Not really (although I'm sure a few are). But rather, it's because racing is challenging enough without having a vast array of gauges, meters, and dummy lights bombarding and distracting you with extraneous information. The more attention a driver can pay to the task at hand, the faster and more consistent he (or she, of course) will be. Perhaps thinking that we need as much help as we can possibly get, Brian Richards at M2 Performance reconfigured our cockpit into something that resembles that of his racecars. The first thing to go was the handsome 2 5/8-inch triple gauge pack (coolant, exhaust gas, and oil temperature) from Auto Meter that nestled in our glove box. In its place, Richards installed a microprocessor-controlled 52 mm dual gauge from SPA. Monitoring both fuel pressure and coolant temperature, the SPA gauge offers a selectable back-lit display, a low battery warning, and individual warning lights that can be programmed to respond to any user-definable threshold. In the quest to avoid redundancy, we also removed our Auto Meter 2 1/8-inch electronic fuel pressure gauge from the driver's side A-pillar. Only needing our Auto Meter boost gauge in plain sight, we relocated it from the A-pillar to the top of the steering column, held in place by an attractive, RX-7-specific gauge holder from GReddy.

Once the gauges were all operational, Richards installed a clever little device designed to emit an audible warning alarm anytime our J&S Safeguard knock sensor unit retarded ignition timing beyond a certain number of degrees. A warning alarm would indicate a bad tank of gas, lean run, or a host of other causes that can spell instant doom for a rotary engine if gone unchecked. Again, this threshold can be adjusted. For our purposes, we set the alarm to trigger if total ignition retard exceeds 5 degrees. Large enough to keep it from buzzing away all the time due to noise-related J&S activity, but low enough to draw our attention to significant amounts of ignition retard.

The benefits of warning lights and audible buzzers should be obvious. Instead of constantly having to read and interpret needle positions and count LEDs (as with the J&S Safeguard monitor), now we just need to notice a warning light or hear the warning buzzer. Still, easier said that done. Imagine driving on the track. The windows are down. You're wearing a full-face helmet. The sun is in your eyes. You're weaving your way through a slew of slower moving cars. You can't hear any buzzer! Nor do you have the time to look across the cabin to check for any warning lights! All of a sudden, you realize that you're using your time and limited brain power for reasons other than trying to keep yourself from flying off the track. Well, that was our situation at least. What's the solution?

How does an SPA steering wheel with integrated warning lights sound?

That's right. We're talking authentic racecar technology now. On the top of the steering wheel, there are three warning lights--each corresponding to a different gauge output. In our case, the three outputs are fuel pressure, water temperature, and J&S activity. If any of these readings exceed (or fall below, as is the case of fuel pressure) our user-determined thresholds, an LED is activated. The downside? We had to give up our air bag. [Readers are urged to keep in mind that the removal of a passive restraint system may have legal, liability and safety implications. In other words: proceed at your own risk and discretion.] As if Project RX-7 wasn't raced out enough, we couldn't resist the idea of a Willans four-point harness system, also available from M2 Performance. While the stock seat belts served us well (once cinched and locked in place), the additional grip levels afforded by the Hoosiers literally had us trying to hold on by the seat of our pants. In fact, after a long weekend of track testing, it wasn't unusual for us to notice a peach-sized patch of irritated skin on the side of our left knees. The cause? Trying to brace ourselves against the door panel with our left legs during hard cornering. With a proper harness holding us firmly in place, we found ourselves spending less energy trying to fight the laws of physics. Our knees are a lot happier as well. Double bonus.

More Electronic Trickery

Every now and then, we actually come up with a good idea. In this case, the revelation was sparked by the performance of M2 Performance's nifty little Knock Alert device. Originally designed to trigger a warning buzzer when the J&S Safegaurd becomes overly active, the Knock Alert could be modified to be even more useful. How does a boost cut sound? It sounded pretty darn good to us. Implementing this function was actually quite simple. In fact, we used same output signal that triggered the buzzer to trigger a relay that would then cut power to an electronic boost controller. What boost controller? We chose to use a GReddy Profec-B. Like all electronic boost controllers, the Profec-B employs a solenoid box which intercepts and attenuates the wastegate signal until the desired boost is achieved. Unlike other boost controllers, the Profec-B does not incorporate fuzzy logic to optimize boost response. Strangely enough, in the case of an RX-7, this missing feature is not missed at all, due to the fact that sequentially operated twin turbocharger systems tend to "confuse" fuzzy logic boost controllers, often resulting in over-boost and erratic turbo performance. For an engine that can hemorrhage itself to death with just one or two good pings, it is our belief that fuzzy logic is best avoided for this particular application.

Installation was relatively straightforward, with much of the time spent removing the intake box in order to gain access to the secondary turbocharger's wastegate control line. Once revealed, we removed the stock vacuum control line that ran between the compressor outlet and wastegate actuator. In its place, we routed the GReddy-supplied vacuum lines to and from the black plastic solenoid box, which we securely mounted in a spacious nook just beside the ABS plumbing. Tweakers should note that the stock wastegate line, which we had removed, contained a small brass restrictor pill which is commonly replaced by tuners to raise boost pressures. Per GReddy's directions, we installed the supplied replacement wastegate lines with no such boost-manipulating restrictors. The reasoning? Because now we have a programmable solenoid! With the wastegate pneumatics in place, we passed both a manifold vacuum line and the solenoid box's wiring harness through a passenger-side firewall grommet, under the carpet, across the center console and into the back of boost controller, which we then covertly hid in the deep crevice between the transmission tunnel and driver's side seat. (We're still working on a more elegant permanent location.) Once supplied with power and ground, the system was up and running. First, we turned the boost controller off in order to determine our absolute minimum boost level. With the solenoid now non-operational, the turbo spooled to a nice, conservative--almost stock--9.5 psi of boost. Why so much boost, despite the removal of the wastegate line's restrictor pills? Our guess is that the solenoid box itself, even unpowered and inactive, is offering a significant amount of signal restriction. This would suggest that 9.5 psi is about as low as we can go without actually having to get our hands very dirty by swapping out wastegate springs. Fortunately, we felt that 9.5 psi was ideal for our knock-triggered, low-boost "fault" mode.

Now comes the tricky part: Tuning. As we know by now, the 13B-REW is not tolerant to over-boost conditions. In fact, a couple good pings is all it takes to fail an engine. Of course, by having the J&S Safeguard installed, we have minimized or risk substantially. Nonetheless, being conservative and employing a little common sense is always the preferred method of rotary tuning. On the face of the Profec-B, there are three knobs: low boost, high boost and something called "Balance." The first two knobs, as one could imagine, are used to dial in boost levels for both the high- and low-boost settings. The third, however, is a bit more insidious, as it used to adjust the response speed or "sensitivity" of the solenoid control. With the knob turned fully counterclockwise (labeled "Mild"), boost response can be maximized. Downside? Possible boost spiking. Ugh. With the knob rotated clockwise (towards "Sharp"), boost spiking can be eliminated completely. Downside? Possible boost fluctuations or "pulsing." Annoying, but not exactly harmful. When tuning, it's important to realize that the boost controller is only really controlling the secondary turbo. This means that one must be extra cautious at turbo transition, as boost levels could instantly spike well into the danger zone. With that in mind, we started out by setting boost knobs at their lowest possible settings and adjusted balanced control toward "Sharp." Starting on the low-boost setting, we carefully adjusted the low boost level knob until we achieved 11 psi. This was accomplished with the balance knob turned fully clockwise and the low boost knob set at approximately the 12 o'clock position.

Next up was the high boost, which to our surprise, started where the low-boost setting ended. In other words, at its minimum setting, boost was already slightly higher than 11 psi. More frightening was the fact that even a tiny, minuscule, hardly noticeable adjustment resulted in an extra 2 to 3 lbs of boost! With a steady hand and watchful eye, we finally managed to get our high boost setting to deliver a steady and consistent 12.5psi of boost. Phew. And once our trick M2 Performance Knock Alert gets triggered, it trips our little relay which then cuts 12 volts power to the boost controller. When this occurs, the solenoid box goes limp, and voila--instant boost reduction! Mission accomplished. We're gushing with pride. Coming up...

So there you have it--a streetable racecar that doesn't give up too much utility or punish the daily driver unnecessarily. It's easy to drive and fast as all hell. Chicks dig it as well. At least that's what I'm hoping. OK, we'll admit that perhaps the least forgiving aspect of the car is the harshness of its suspension. Over rough, broken pavement, it's not the ideal source of transportation. While it's heads above many other modified cars we've driven, it's still firmer than most people would prefer. Right now, there's little that we can do about it. That is, in order to ease off on the low-speed compression damping that causes this harshness, we would have to give up some rebound control which is vital to the car's at-the-limit handling performance. (Remember, we are using heavy rate springs that are nearly three time stiffer than stock!) Next issue we'll approach this situation from a different angle. Instead of relying on adjustable off-the-shelf shock absorbers to handle damping duties, we'll see if we can dial-in something that offers independent compression and rebound adjustability. Done properly, this should not only improve ride quality, but ultimately performance as well. A little more horsepower can't hurt either. Stay tuned!