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Mazda RX-7 GXL For the new rotary runner, more refinement and better behavior by Larry Griffin -- Car and Driver -- November 1985
Mazda had a winner in the RX-7 from day one. Introduced in 1978, its Wankel engine provided a hearty sportiness that wooed sales from increasingly glitzy and hefty competitors. The original RX-7 lasted a phenomenal seven and a half years.
The new RX-7, except for its nameplate, general layout, and basic engine design, is all new. Mazda offered us two chances to drive pilot-production versions of its rotary toy, and we zipped all over Southern California and Washington state.
Yes, you've seen this car before. The new nose looks quite Porsche-like. The sides are straight off a Daytona Turbo Z. The rear has been rounded up from a Camaro Z28. The wheels look as if they were nidnight-auto-supplied from an Opel Senator. Fortunately, the collage is attractive. All the badges were camouflaged on the car we drove in California, and passers-by always blurted the same question: What is it? The nose and the tail wear plastic bumper beams and fiberglass-reinforced urethane bumper covers colored to match the body. "Flash to pass" light ports snuggle in the front bumper just below the retractable halogen headlights; articulated linkages allow the headlights to sit upright when retracted, so the same lever that switches between low and high beam at night will also flash passing warnings through the ports when the lights are down for aero efficiency during the day. In this retracted state, the new RX-7's basic drag coefficient is 0.31, and it drops to 0.29 with an optional aero package.
Mazda intended to build a much more solid unit body for the new car, and the old RX-7's tinny feel of panels and pieces rustling together is indeed gone. Shored up by massive window frames, the doors clump tightly shut. The structure feels rigid—no hinges, no twinges. And,, although the overall length has shrunk 1.2 inches, to 168.9, the wheelbase has been lengthened 0.4 inch, to 95.7 inches. The track and the overall width are each increased roughly an inch, and the curb weight is up to 2700 pounds, roughly 100 pounds more than the old model. At the anguished request of dealers and rug rats, Mazda is finally offering a two-plus-two option in the States. The new RX-7's folding back seat is about the size of the one in the 944: minuscule. Unlike the famous stretched Nissan Z two-plus-twos, the four-seat RX-7 shares the same basic body shell with the two-seater.
In offering additional seating positions and more contemporary styling. Mazda is obviously responding to the wants and needs of the market as it did so brilliantly in 1978, when the original RX-7 was introduced. However, this time around, value is not the single-minded priority it used to be. The early word is that base prices will start at around $12,000 for the two-seater and step rapidly upward, peaking out at about $18,000 for the leather-lined and compact-disc-player-equipped GXL.
In tooling up for a new car, Mazda considered three basic alternatives. The first was to face-lift the RX-7 without major chassis changes. The second and wildest option was to redo the whole car and go for broke with an electronic-display instrument panel, a rear-mounted transaxle, electronically controlled power steering, and a fully independent and self-adjusting suspension. The third alternative (and the one picked) was a slightly more conservative approach: no video-arcade instrumentation and no transaxle, but bring on the best suspension, brake, steering, and wheel-and-tire hardware available to make the RX-7 competitive in performance with whatever the world has to offer for less than $20,000.
Like every carmaker these days, Mazda was after better handling. The idea was to induce the RX-7 to track as if by second nature, and to turn into corners crisply, but to avoid the old rear-axle side step at the limit. Both the standard model and the GXL share a new rack-and-pinion steering gear designed with high rigidity in mind. To enhance straight-ahead feel, the rack itself has been machined with a 0.5mm bulge at its center to tighten rack-to-pinion contact at this critical point. To upgrade GXL models, Mazda gives them a special electronically controlled power-steering system. Sensors monitor road speed and steering angle every 0.3 second and feed this information to a computer that varies the power-steering assist supplied by two tandem hydraulic pumps. The harder you drive, the less the assist. The results are very light, enjoyable steering at low speeds, and firm, stable tracking at high speeds.
Mazda's anti-oversteer solution, called Dynamic Tracking Suspension System, involves a semi-trailing-arm rear suspension, a design normally known for inducing tail-happiness. In this case, however, bad habits are held in check by an amazing array of mechanical Band-Aids. Complex linkages and bushings react to fore-and-aft and lateral load and in doing so coerce the rear geometry into steering for better instead of for worse (see Technical Highlights). As unlikely as this sounds, you can indeed feel it working. At the first sign of your steering input for a hard corner, the car dives for the apex and the rear tires get to work pronto. You think maybe you've overdone it as you feel the tail get up to step out, but then the set of the chassis retreats through neutrality and cossets you back into understeer.
The RX-7's quick steering response owes much to the front suspension's modified MacPherson-strut layout. Forged-aluminum control arms and wheel hubs were chosen to provide the necessary stiffness with the least unsprung weight, and the suspension's mounting system is specially designed to resist lateral and twisting forces while discouraging dive during braking. Longitudinal stiffness through the rubber mounting bushes is low to minimize impact harshness over bumps.
The RX-7's ride qualities can be adjusted by switching the console button for the Auto Adjusting Suspension from the normal to the sport setting. Sensors monitor car speed, lateral acceleration, longitudinal acceleration and braking, and steering-wheel angle. A microprocessor analyzes the information, then picks the desired damping from three possible settings: normal, firm, and very firm. When the driver chooses normal, he gets the normal setting both front and rear up to 50 mph, then a firm setting in the front beyond that speed. IN the sport setting all the shock absorbers operate in the firm position until the microprocessor detects notable destabilizing forces, at which time the valving is switching to very firm at all four corners.
The rolling stock is low in profile to benefit from the latest tire technology on the market. Base cars were 185/70HR-14 tires on 5.5-inch steel or aluminum wheels, and the GXL gets 205/60VR-15 tires on 6.0-inch-wide alloys. The RX-7 Turbo, when it arrives in a few months with another 40 or so horsepower, will war V-rated 205/55s on 7.0-by-16 alloys.
The heavily finned, forged-aluminum, four-piston front brakes and the single-piston rears squeeze ventilated rotors, and they feel good through the pedal, production few doubts either in scorching mountain runs or on the test track, in 186-foot stops from 70 mph. Few cars tell you so clearly that worthy mechanical bits are working in your favor.
Under the hood, a long list of rotary-engine improvements keeps the RX-7 humming along nicely in its new, more upmarket role. Last year, two displacements were offered, but only the larger 13B engine is back for 1986 duty. It displaces 1308cc (compared with the original RX=7's 1150cc) and breathes through a sophisticated six-port, tuned-length induction system. Fuel delivery is through four injectors managed by a digital electronic engine-control computer. Thanks to Mazda's persistent development of the rotary, the RX-7's power, torque, and fuel economy are all improved: compared with last year's 13B, there are ten more horsepower, five more pounds-feet, and about one more mil per gallon (both city and highway) to play with. If this isn't enough to tickle your interest, Mazda has the turbocharged 13B on the way, as well as intentions of unveiling a pure-racing three-rotor engine sometime during 1986. Yes, sports fans, the new car's engine bay is roomy enough to swallow this triple-scoop rotary if it becomes practical for production.
On the road, today's two-rotor, normally aspirated rotary feels quite lively, quicker to respond than its predecessor, perhaps because the former howling exhaust hum has been muted. The fifth wheel freezes the swift-moving RX-7 at 7.7 seconds from 0 to 60 mph and 16.0 seconds at 86 mph for the quarter-mile. Mazda claims a top speed of 128 mph. All in all, the new and heavier is about as quick as a 1985 GSL-SE, so it's clear that the more potent engine and the cleaner aerodynamics are working in your favor.
In the cockpit, the shifter and the pedals are sturdier, and they're placed better than ever. The seats are genuine wraparound performance items, multi-adjustable for proper support and reach to the tilt-adjustable wheel. Unfortunately, the extra-cost leather upholstery may drain performance out of a hot driver in warm weather, even when the otherwise adequate air conditioning is pumping at its upper limit. The instrument layout is first-cabin, but the red-orange markings can be less effective than pure white-on-black markings, especially on a sunny day when sunglasses mask detail in the depths of the instrument pod. The rest of the RX-7 ergonomics are fine. Love those wacky pinball-flipper controls on the dash pod that keep the wipers and the smooth cruise control in play.
There are two things we'd get rid of for sure: the two-spoked steering wheel, for a proper three- or four-spoked sport wheel; and our old RX-7, if we had one, for a new RX-7. Then we could go out and give fits to folks in old RX-7s. But then, human nature being what it is, those folks will just slip into the RX-7 Turbo the moment it rushes ashore, and the escalation will start all over again. The RX-7 does nicely in this escalation business: a winner from day one, still a winner.
Rotary Refinements
Improvements to Mazda's 13B two-rotor Wankel for 1986 include: a new microprocessor-based engine-management system to control fuel delivery, ignition, and emission controls; relocated spark plugs (leading and trailing igniters are now 5mm closer together); a new multi-chambered exhaust-port inset to soften the exhaust note; a dual-muffler exhaust system; reduced cooling-jacket capacity (to speed warmup); rotors that are lighter by fourteen percent; a thick steel liner for the rotor housing; a new Teflon coating for internal wear surfaces; and twelve instead of nine eccentric-gear mounting pins for increased strength. Horsepower and torque are up by seven and four percent, respectively. In addition, EPA city and highway fuel-economy figures are both up by 1 mpg (with a five-speed transmission).
Technical Highlights : A semi-trailing-arm suspension as new as the RX-7
by Csaba Csere
Suspension innovations are few and far between at most car companies, but they're regular occurrences at Mazda. The 19780 GLC was born with an intriguing multi-link rear suspension, and today's 626 benefits from an unusual asymmetry in its front suspension. Mazda engineers are currently studying four-wheel steering for future models.
With the new RX-7, Mazda has undertaken the noble task of eliminating the vices of the semi-trailing-arm rear suspension. In doing so, its engineers have created one of the most complex rear suspensions ever used in production, and one that bears only a vague resemblance to the original semi-trailing-arm design. Three new features have been added on each side: a double-jointed connection at the trailing arm's inner attachment point, an extra diagonal link, and a very complex mounting hub between the wheel and the trailing arm.
The purpose of the double-jointed connector is to split two key functions of the suspension hardware. It allows the trailing arm's inner member to manage wheel camber while the longer diagonal link provides excellent lateral location of the heel.
Mazda engineers have added the exotic hub to finish the job. Any suspension has some tendency to toe (steer) the rear wheels in and out under various acceleration, cornering , and braking forces, and Mazda has applied the special hub to use this natural tendency to best advantage. Located between the wheel carrier and the trailing arm, the hub consist of two flexible rubber bushings and one inflexible steel bearing, each of which acts as a combination mounting and pivoting point. Two of the pivots form an imaginary kingpin axis analogous to a front suspension's; the third performs a restraining function analogous to a tie rod's During normal running, the rear wheels point straight ahead to minimize tire wear and rolling friction, but under cornering loads, deflection of the semi-trailing-arm allow a slight amount (less than 0.2 degree) of tow-out. Mazda engineers feel that this sharpen the steering response by helping the car yaw (rotate about a vertical axis) more quickly. Excessive toe-out can cause instability, so at about 0.4g, the leader rubber bushing in the hub starts to deflect, causing the wheel to start toeing in. As cornering loads increase, toe-in reaches more than 0.5 degree, promoting understeer and enhancing stability.
Mazda's floating hub also produces toe-in during acceleration and braking. The aforementioned imaginary kingpin axis shifts in such a way that longitudinal forces cause the rear wheel to toe in slightly, increasing stability.
Other manufacturers will undoubtedly scoff at the complexity Mazda has gone to in the new RX-7 rear suspension, but that won't change this company's reluctance to accept old compromises when a new model is in the offing. At the very least, Mazda has shown that, with enough determination, even the 28-year-old semi-trailing-arm design can be taught a few new tricks.