Third Generation Power Plant and Drivetrain Benefitstaken from "RX-7: From Race Car to Sports Car"
All of the qualities that have made the Mazda rotary engine a track champion make it an ideal powerplant for a pure sports car on the street. In fact, the entire RX-7 design - the front mid-engine layout, the near-perfect 50/50 weight distribution, even the styling - is inspired and made possible by the size, shape and output of its rotary engine.
The rotary engine is physically compact and lightweight. It's durable. The basic design has only three moving parts: two rotors and a crankshaft. There are no valves, no cams, no lifters.
A reciprocating engine expends a significant portion of its power potential in converting the linear motion of its pistons to the rotational motion of the crankshaft and in overcoming the friction of many moving parts. But the rotary engine generates rotational motion from the start. It revs freely and produces an extraordinarily smooth flow of power. And the driving feel previously reserved for hand-built exotics.
And a prodigious amount for its size and weight. The rotary in the RX-7 puts out 255 horsepower at 6500 rpm and 217 lb.-ft. of torque at 5000 rpm. The resulting horsepower-to-weight ratio puts the Mazda RX-7 into the front rank among the world's fastest production sports cars. Zero to sixty: 4.9 seconds. Top speed: 250 km/hr.
In creating the 13B engine that powers the RX-7, Mazda engineers drew upon over 30 years of rotary research, development and refinement. Every major component - the intenal parts, the intake system, exhaust system, cooling system, electrical system - has been extensively modified or is completely new.
And from the start, the engine was intended for turbocharging. With ports instead of valves and with a natural supercharging effect in normal operation, the rotary engine is an ideal candidate for turbocharging.
RX-7 Mazda engineers took full advantage, designing a sequential twin turbocharging system. A few other cars offer twin turbos. But the Mazda RX-7 is the only production sports car in the world to employ them sequentially. (In the more usual tandem setup, the two turbochargers work together over the full rpm range. This increases high-rpm performance but has little benefit at lower engine speeds).
In the Mazda sequential arrangement, the first turbo supplies boost at lower rpm, receiving the full force of the exhaust. So throttle response is instant. As revs climb, the second joins in, giving the same high-rpm boost as a tandem design. To further increase power, an intercooler cools the intake air so that the turbochargers can force more air into the rotor chambers. The intercooler is located in the nose to get the full benefit of a direct air stream.
Taking the best advantage of all the power and revs this engine has to offer demands a transmission that can deliver quick, precise and smooth shifts. So the RX-7 has a newly developed 5-speed with a double-synchro mechanism in the three lower gears for greatly increased torque capacity. Revised and refined linkages provide short throws with a very positive feel.
Even the differential is out of the ordinary in the RX-7. It's a Gleason Torsen unit, an ingenious limited-slip design. A limited-slip differential provides handling advantages on slippery or uneven surfaces. If one rear wheel loses traction, more torque is transferred to the other wheel. Widely used in race cars, the Torsen differential is up to twice as effective, depending on conditions, as a conventional viscous limitedslip design. And torque is transferred in a much more linear fashion.
No other car in the world offers this kind of drivetrain. Unless, perhaps, you land yourself a ride in IMSA GTP. Or maybe at Le Mans.
written by: www.mazdausa.com (1996)