Fd3s:scc project car

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