If you're a gearhead, there's a chance you love rotary engines as much as I do. The unique and angry sounds they make, their high redlines, and Mazda's daring at making an unconventional engine long after the other automakers abandoned it have all given the rotary engine a cult following. But despite their charm, the rotary engine has disappeared from the new car world, a victim of emissions and fuel economy concerns.
Though you probably already understand how the rotary engine works, neatly combines a brief review of how it runs and an explanation of why it's so inefficient.
By design, Wankel engines have a uniquely shaped combustion chamber. This results in unburnt fuel being sent through the exhaust. Added to the fact that sealing off the different chambers of the engine is difficult, and that oil is being injected directly into the combustion chamber, it becomes obvious why the rotary engine gets abhorrent gas mileage.
Exactly how bad? points out that a Volkswagen GTI, with similar power and weight as the RX-8, is 55.5% more fuel efficient. Some of that is inevitable—front-wheel-drive layouts almost always get better fuel mileage than rear-wheel drivetrains thanks to less friction losses, and the GTI has always emphasized efficient performance, whereas the RX-8 was an enthusiast car through and through. But that difference isn't something you can ignore easily.
With EPA regulations tightening for all automakers, it makes perfect sense why the rotary engine is currently dead. All is not lost, though, as Mazda confirmed back in October that the rotary engine will make a reappearance and be called the SkyActiv-R. Rumors of the application fly far and wide—maybe it will be an RX-9, maybe it will be an RX-7. Hell, maybe it will be a 450-hp, twin-turbo engine. That should definitely help with the fuel economy.