Where do you start withMotor Corp.’s new Renesis rotary? That we’re just plain delighted to see the rotary architecture return to thrill drivers with its eerie high-rpm smoothness? That the engine Mazda doggedly has made virtually its own since the 1960s is vastly improved, yet emotive as ever? Or that even with this new-age variant, the rotary has its critics, its foibles?
Its long-term implications for the powertrain sector remain for history to decide, but we’ll vouch for one aspect:’s new Renesis rotary handily carries on the near-mythic qualities that have earned it one of the most rabid enthusiast followings of any engine in history.
Central to the rotary mythos, of course, is the engine’s basic motion: rotary rather than reciprocating. Because the Renesis’s two trochoids – triangular-shaped rotors with an indented “combustion chamber” in each of the trochoid’s three sides – revolve in a motion that’s essentially circular, the Renesis spins to spectacularly high rpm. Witness the ambitious 7,500-rpm power peak and 9,000-rpm redline. The rotary motion’s advantage is described by Mazda as “theoretical near-perfect dynamic balance with torque fluctuation equal, if not superior to, an inline 6-cyl. engine.” All we know is this: Ram the Renesis to 9,000 rpm and vibration is all but non-existent.
|Mazda’s signature rotary returns to U.S. with new Renesis.|
The Renesis’ primary innovation over previous generations of Mazda’s 2-rotor Wankel design is the location of the exhaust ports on the engine’s side housing. By doing so, engineers were able to eliminate or reduce many of the rotary’s intrinsic combustion/exhaust-related bugaboos, which primarily were related to emissions and fuel economy.
The “High-Power” version of the Renesis is differentiated from the standard-power version that generates 197 hp by virtue of a more-complex variable-tract induction system, three rather than two fuel injectors per rotor and an elaborate intake port design that incorporates an extra port governed by a rotating valve that Mazda engineers say effectively amounts to variable valve timing for an engine that has no valves.
The Renesis intake and porting layout is astoundingly complex, and even after engineers explained the system and showed us the diagrams, we’re still not entirely certain how it works.
We just know it works. Judges’ favorite Renesis quality is its primal, mechanical exhaust snarl, which doesn’t approach its full epic potential until pushing past 6,000 rpm (one judge says it’s the sound you’d expect when wringing the neck of the beast in the movie Alien). You find yourself enjoying the snarl for other reasons, though, as the Renesis’ meager 159 lb.-ft. (216 Nm) of torque demands frequent replays to extract maximum performance.
And although the new side-exhaust is claimed to pay extensive engineering dividends, the advantages outside the realm of thermodynamics are difficult for non-engineers to absorb. For example, the new design is claimed to enhance fuel economy (since its inception, the rotary has borne a reputation as a gas guzzler), but we find it tough to praise SUV-like thirst in a 3,000-lb. (1,361-kg) sports coupe. Other high-performance cars at least manage to eke acceptable highway mileage, and we suspect the RX-8’s super-short 4.44 rear axle.
But in reality, our criticisms are window dressing. Ward's judges were overwhelmed by the Renesis, plain and simple. Mazda’s new rotary is a fascinating technical achievement and a superb, emotional performance-car engine.
|1.3L Renesis Rotary|
|Engine type||1.3L twin-rotor rotary|
|Bore x stroke (mm)||NA|
|Horsepower (SAE net)||238 @ 8,500 rpm|
|Torque||159 lb.-ft. (216 Nm) @ 5,500 rpm|
|Specific output||183 hp/L|
|Fuel economy |
for tested vehicle
(EPA city/hwy. mpg)