So what is this engine anyway? It's not a piston engine?


You may have heard that this engine is not a piston engine. This is correct, despite ignorant people that insist "all engines have pistons!". The RX-8 is powered by a rotary engine, based on the principle design developed by Felix Wankel, from whom Mazda bought the exclusive rights to develop. The rotary engine is very hard to describe with just words, so here are a few pictures:

Exploded view of the engine and it's component parts


All put together:

Image from Pineapple Racing

The total package is quite small compared to piston engines: (That is one rotor, housing, and the eccentric shaft)

Image extracted from a video published by Mazdamaniac.com

So, How does it work?

Basically, the combustion sweeps the rotor around the e-shaft in an off-center looking wobble. (This is actually an RX-7 engine, but the basics are still the same)

Image from RotaryEngineIllustrated.com

Here is a good YouTube video of the components and motions of the engine:


Dramatic difference from the traditional piston engine.

So, as you can see, we have 3 combustions per rotor for every full rotation of each rotor. However, due to the gearing reduction around the e-shaft, each rotor spins at 1/3rd the speed of the e-shaft. So when you are at 9,000rpm, each rotor is only spinning at 3,000rpm, however each rotor is producing 9,000 combustions per minute, for a combined total of 18,000 combustions per minute. This is most of what produces the buttery smooth power delivery of a rotary engine. You can also see that the motion is already rotational in nature, rather than the continual start/stop of pistons in a piston engine. This is the other main contributor to the smoothness of the engine.

Our "lack of torque" is also a byproduct of this. Each combustion is quite small, and there isn't much leverage provided by the e-shaft angles.

So what makes our engine different from prior RX-7 engines that are also listed as 13b engines?

Primarily, the difference is the location of the intake and exhaust ports.

Image from Mazda.com

RX-7 engines had their ports on the rotor housing, so the apex seals sweep across them.
RX-8 engines, the Renesis, have the ports on the end plates and center iron. This means that the apex seals do not sweep across them at all. This enables unburnt gasoline in the exhaust post-combustion to be more likely to stay in the engine to be burnt the next time around, rather than getting swept out into the exhaust system. This improves emissions and fuel economy.

The other primary different from the RX-7 engines is that the Renesis has higher compression rotors, also in the name of power, emissions, and fuel economy.

There are many more differences, and they are differences that often trip up RX-7 experts that don't fully consider the implications of the major design changes, so be wary of someone that professes expertise on the RX-8 because they have expertise on the RX-7. They need to gain the RX-8 expertise all on it's own.