SA22C:Reviews
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First Drive: 1978 Mazda RX-7
Sleek, Functional and Fast: An Affordable 2-Seater For the Enthusiast From the May, 1978 issue of Motor Trend Chuck Nerpel
Editor's Note: This year, Mazda celebrates its 90th anniversary and along with an extensive retrospective coming on May 20, we've gone through the archives to bring you a look at several classic Mazdas from the 70s and 80s.
The oft-rumored, long-awaited Mazda RX-7 sports car is now a reality. Since 1974, rumors have persisted that Toyo Kogyo was preparing a brand-new, rotary-powered, sports-type vehicle to compete primarily in the American market with the Porsche 924, Datsun 280Z and, possibly, the Corvette. The rumors were well-founded, as the project, under development during the last four years, was finally revealed to a select group of American automotive journalists in late February at the Hiroshima factory.
Unlike many American car makers, where information becomes available through planned or surreptitious "leaks" and the testing facilities are not that secure from the all-seeing telephoto lenses of zealous journalists, Japanese automakers can keep a secret if they have a mind to. The testing facilities on the outskirts of Hiroshima are ultra-modern with everything from a high-banked track, electronically timed dragstrip and a variety of roughly paved areas, to dirt roads and water baths. Located as it is in a heavily wooded area, patroled by security guards and surrounded by a high barb wire-topped chain link fence, it is virtually "spy proof."
So, after four years of speculating on the new RX-7, there they were, three sleek aerodynamic coupes sitting on the tarmak of the test track alongside a 924 Porsche. Obviously, the area of competition for the RX-7 is not very subtle. "For comparison," was the polite answer as to why the Porsche presence, but just as politely, the Japanese courtesy did not include another obvious competitor, the Datsun 280-2.
Three of the new cars were available for testing: the standard model with 4-speed transmission, a GS version with 5-speed transmission and radial tires, and one equipped with the optional automatic transmission. The base model, tentatively priced to sell for "under $7000" depending on the dollar/yen exchange, comes with tachometer and inset voltmeter, quartz clock, reclining bucket seats, tinted glass, AM/FM/stereo radio, front anti-roll bar and 165HR-13 steel-belted radial tires. The optional GS package ($500 extra) includes all of the above plus a 5-speed transmission, electric remote rear hatch release, protective body molding, rear anti-roll bar and 185/70 HR-13 steel-belted radial tires. Additional options include tilt-up removable sunroof, air conditioning, automatic transmission and alloy wheels. All models are powered by the 12A twin-rotor 70-cid engine that developes 100 hp at 6000 rpm.
Toyo Kogyo has no doubt spent more time, money and research on the rotary engine than NSU, first to power a passenger car with such an engine; Porsche-Audi, which sells an Audi R08 in Europe; Curtis-Wright, with many experiments for a light aircraft engine; and General Motors, which finally shelved efforts to build an acceptable rotary powerplant.
Mazda's engine development over the past 15 years has not been without problems, and many owners of RX-2s, '3s and '4s were plagued with expensive seal replacements and some seized engines, all of which does not project a good image of reliability. Then there was a rather fruitless argument between the American distributor and EPA over gas mileage figures, all of which spurred Mazda to even greater research of the non-reciprocating engine principle. They firmly believe, and are out to prove, that this configuration can be reliable, give good gas mileage and meet current and future emission controls. Besides, there are some inherent advantages that make it an ideal powerplant for a sports-type car. It is compact, light in weight, virtually vibrationless, quiet and has a smooth flow of power through the entire rpm range. This, then, was the logical choice as an engine for the RX-7. After all, they have built 930,000 rotary-powered passenger cars and light trucks, in addition to sponsoring some successful racing cars.
The RX-7 is not Mazda's first sports car. Way back in 1967 they introduced the Cosmo 1105 which placed 4th in the 1968 Le Marathon de la Route 84-hour endurance race. But sports car concepts have come a long way since then, and the new version is an aerodynamic, wind tunnel-tested, beautifully styled piece of machinery. It has smooth lines, not unlike the Porsche 924 in front, except for the color-keyed, integrated bumper. The rear treatment is entirely different, with a large, unframed glass hatch, large combination taillights and a full-width bumper. Mr. M. Maeda, chief stylist, said there were no styling restrictions, no orders to make it look like any existing competitive car. They began with a clean drawing board and attempted to achieve a package with lots of interior room, low coeffecient of drag, high visibility all around, integral roll bar-type roofline, a greenhouse likened to a modern jet aircraft, and a bit of the original Cosmo 1105 identity.
Wind tunnel tests were conducted with full-scale models at the Japan Auto Research Institute and slight changes made to achieve a very low (.36) drag coefficient. The pop-up headlights increase this by 6%, bringing it to .381, still quite low. The body is all steel, welded into a solid unitized package with extra box framing around the passenger compartment and side impact bars in the doors.
To describe the styling, which is largely a matter of personal opinion, it is slippery looking, pleasing to the eye with no glaring defects or harsh panel-dividing strips to mar the smooth appearance and meets the original criteria of the stylists.
The interior design is strictly contemporary sports car, with center console housing parking brake, shift lever and radio and heater controls. The instrument pod is centrally located for a good view by the driver through the laterally spoked, leather-covered steering wheel. Bucket seats are full reclining with ample for and aft adjustments. A large flat area behind the seats will carry plenty of luggage for two for a week or a weekend.
The entire RX-7 package is unique in that the front engine, rear-wheel drive, steering, front and rear suspension and braking system are rather conventional but work as well as some rather highly sophisticated designs used in competitive models. Mid-engine designs were explored during the initial research, but with the front of the light, compact rotary engine located behind the front wheel center line, and the central passenger position, it was possible to achieve a near 50-50 front-to-rear weight distribution and a 2350-pound curb weight with such a configuration.
The front suspension is independent, using the McPherson coil and shock strut with anti-roll bar and tensioning rod for front and rear location of the lower strut. The lower part of the coil spring is tapered to permit positioning closer to the king pin axis, providing narrower steering offset, reduction of vibration transmission to the steering wheel, and more stable braking. A recirculating ball and nut steering system was adopted over rack and pinion, because it requires less steering effort, transmits less road shock to the steering wheel and, with the beefed-up unit used, seems to be a happy medium between the two systems.
At the rear, the solid axle is suspended on coil springs and located by 4-link longitudinal arms and laterally with race-proven Watts linkage which allows precise location of the roll center. Gas-filled shocks, widely spaced and nearly vertical, are valved for equal bound and rebound and were selected because the damping force varies with the speed: soft on low-speed bumps, stronger on severe, high-speed bumps. The rear suspension does work very well at both high speed and on winding roads, but it judders and wheel hops on maximum acceleration from a standing start. Dual-angled shocks and/or firmer rubber bushings in the 4-link arms could be a solution, but the Mazda engineers were noncommittal when asked about this problem. Knowing the Japanese, the auto writer's comments were carefully noted by the engineers present, and it's a very good bet they are working at it right now.
Like the chassis and suspension, the braking system with power-assisted front discs and rear drums is conventional, but this combination works very well. Anti-dive geometry, near-equal weight distribution and balanced valving between front and rear provide excellent stopping power. Under maximum-effort stops the RX-7 just squats with little front-end dive and all four tires take hold of the pavement. Any car that goes and handles as well as this one must have a braking system that is predictable, and the 9-inch vented front discs and 8-inch vented rear drums withstand repeated full-pedal stops with no sign of fade or erratic behavior.
Acceleration with two aboard is quite good, considering the rated engine size of what the Japanese refer to as 35-cid plus 2, the latter meaning 2 rotors. With the manual transmission and a standard 3.9:1 rear axle ratio, 0-60 time was 9.2 seconds, 16.7 for the quarter mile. The automatic is just a bit slower with 10.6 and 18-second clockings. Both transmissions are very smooth, with a positive, short-stroke control for the 5-speed and a center-mounted selector for the automatic. The power flow from the rotary engine is smooth through the entire rpm range, and there are none of the vibration phases that occur in most piston engines. Maximum torque is at 4000 rpm with plenty of power to accelerate from 50 to 70 mph in 4th gear in 6.0 seconds.
Mazda lists the top speed as 120 mph, and the high-speed factory test track with three parabolic banked turns is designed for hands-off 120 mph in the top lane. We were able to indicate 130 mph on the test run and believe the speedometer was pretty close to accurate, as the high lane at this speed was not exactly hands-off but the car was very manageable.
Handling is very precise, and the recirculating ball steering is very close to a rack and pinion system with much less effort. There is just the right amount of understeer on hard cornering. The low center of gravity, good weight distribution and wide stance contribute to a very stable yet quiet, comfortable ride with a good feeling of security. With the optional steel radial tires lateral g force is .84 and speeds of 60 mph are possible through a slalom course of pylons placed 100 feet apart.
Estimated gas mileage is 19 mpg city, 29 mpg highway, 23 mpg combined. Unleaded fuel is recommended, though, and air injector and thermal reactor are used for emission control rather than a catalyst. Mazda is prepared to go to catalysts and Bosch fuel injection, should the need arise with future tighter emission laws.
Production began in early March, and models will reach U.S. and Canadian shores by early June. At present, only a 2-seater model will be exported, though a 2+2 will be available to the Japanese market.
Special engine modifications, front air dam and rear spoiler will be available to modify the RX-7 for racing in SCCA C-Production Class. If Mazda can sell this car, for the proposed under $7000, several competitors are really going to have to hustle to keep up with the RX-7.
Combustion has been improved by modifying the size and shape of the chamber in the rotor, and the position of the leading spark plug has been changed a few mm's. Two plugs per rotor are still used, but the 2-electrode type is now replaced with units having three evenly spaced around the center electrode.
The hot start problems have been overcome by a motor-driven hot start motor that opens the throttle slightly on starts where the water temperature is over 140 degrees F.
A 5-hp increase over previous rotary engines was achieved by changing the contour and enlarging the secondary in take port. This reduces the flow resistance and increases volumetric efficiency, and it is one of the many little changes that add up to larger gains in improved overall performance and gas mileage. On this fuel intake side the carburetor float has been reduced in size and redesigned to prevent fuel cut-off under hard corner ing conditions.
It is obvious that the Mazda engineers have done their homework on this latest rotary engine. The test cells at the Hiroshima factory run day and night testing all types of materials, prototype engines and production engines to prove out the theories for improving performance and reliability. There are no short cuts, and Mazda has nearly 15 years of experiermenting to prove that point. The new 12 twin-rotor is probably the most advanced version of the Wankel to date.
During the long-lead showing of Mazda's new RX-7 sports car the Toyo Kogyo engineers proudly displayed their racing version of the twin-rotor 2-seater. This was just a non-drivable prototype, but it was obvious that a lot of test driving had been done in the development of the add-on "goodies" that will be available through U.S. dealers by early 1979.
Body panels, fender flares, front air dam, rear spoiler and, possibly, the applique stripes are among the functional and cosmetic over-the-counter pieces that can at least make the RX-7 look like a racer. For the serious competitor it is possible to make the "innards" truly functional. First, for an as-yet-undisclosed price, there will be the full-race peripheral-port engine with modified combustion chamber, 2-throat 45 DCLE Weber carburetor and deletion of all mandatory emissions controls that add up to a hp potential of 220 plus.
It still goes hmmmmm but it's a lot more reliable. Felix Wankel, inventor of the rotary engine, was probably aware of the shortcomings of his rotating combustion chamber principle but would be awed by the technology and research employed to overcome these problems. Toyo Kogyo has worked continuously, since the introduction of its first rotary-powered car 10 years ago, to improve the reliability, fuel economy and serviceability of this power plant.
Through the previous decade, while manufactUring about 930,000 rotary-powered cars and light trucks. Mazda engineers gained a great deal of knowledge of the problems and saw the need to use the most advanced metallurgical technology and to develop some of their own processes. Sealing of both the apex or lip and the sides of the rotor was a major problem. Lubricating both the apex seal and the inner case walls required intricate oiling systems in an environment that was ultra-hot with high pressures bearing on both surfaces and fouling by the residues of combustion. Besides, there is a sharp corner between apex and sides, an area that needs near perfect blow-by sealing.
Test and test they did with various metals, coatings and heat treatments. First, a new process called SIP (sheet metal insert process) was developed to cast a steel inner liner into the aluminum alloy outer case. The steel is a special material that is then hard chrome-plated with pinpoint porosity to hold an oil film and reduce wear on the apex seals. These seals, formerly of a special carbon material, have been replaced by an iron-based metal with the contact area crystallized by the electron beam process into a form of carbides called the "chilled layer." The corner "button" type seal, a nonflexible unit, has been replaced by a flexible type designed to expand under combustion and compression pressures, reducing leakage and increasing thermal efficiency.
Side sealing of the rotor was another area where high wear was reduced considerably by a gas-nitrizing treatment applied to the side housing. The treated layer is but a few thousandths thick but has excellent anti-corrosion and anti-rust qualities in addition to being highly wear-resistant.
Combustion has been improved by modifying the size and shape of the chamber in the rotor, and the position of the leading spark plug has been changed a few mm's. Two plugs per rotor are still used, but the 2-electrode type is now replaced with units having three evenly spaced around the center electrode.
The hot start problems have been overcome by a motor-driven hot start motor that opens the throttle slightly on starts where the water temperature is over 140 degrees F.
A 5-hp increase over previous rotary engines was achieved by changing the contour and enlarging the secondary in take port. This reduces the flow resistance and increases volumetric efficiency, and it is one of the many little changes that add up to larger gains in improved overall performance and gas mileage. On this fuel intake side the carburetor float has been reduced in size and redesigned to prevent fuel cut-off under hard corner ing conditions.
It is obvious that the Mazda engineers have done their homework on this latest rotary engine. The test cells at the Hiroshima factory run day and night testing all types of materials, prototype engines and production engines to prove out the theories for improving performance and reliability. There are no short cuts, and Mazda has nearly 15 years of experiermenting to prove that point. The new 12 twin-rotor is probably the most advanced version of the Wankel to date.
During the long-lead showing of Mazda's new RX-7 sports car the Toyo Kogyo engineers proudly displayed their racing version of the twin-rotor 2-seater. This was just a non-drivable prototype, but it was obvious that a lot of test driving had been done in the development of the add-on "goodies" that will be available through U.S. dealers by early 1979.
Body panels, fender flares, front air dam, rear spoiler and, possibly, the applique stripes are among the functional and cosmetic over-the-counter pieces that can at least make the RX-7 look like a racer. For the serious competitor it is possible to make the "innards" truly functional. First, for an as-yet-undisclosed price, there will be the full-race peripheral-port engine with modified combustion chamber, 2-throat 45 DCLE Weber carburetor and deletion of all mandatory emissions controls that add up to a hp potential of 220 plus.
Many of the RX-3 suspension parts used by sports car racers in Japan will be adapted to the RX-7, including heavy duty shocks, springs and anti-sway bars and possibly 4-wheel caliper disc brakes. The prototype on display not only had discs on all 4 wheels, but a parking brake as well, indicating there may be a contemplated change in the production models in the next year or so.
There could be some problems in buying the racing engine in the U.S., as the licensee for the engines is Curtis-Wright, and Toyo Kogyo must work on its agreement with C-W, a pact which permits sale of rotary engines in the U.S. only when packaged as part of a vehicle or imported as a replacement engine for an existing car. There have been some attempts by U.S. engine buffs to modify existing rotary engines, but this is difficult due to lack of advanced technology and required parts.
If current plans are completed on schedule, there is a good chance there will be more than a few RX-7s on the SCCA circuit in 1979.
Read more: http://www.motortrend.com/classic/roadtests/7805_1978_mazda_rx7/specs.html#ixzz0oIyllnGK
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