This is from a website which sells every part in the world related to the rotary engine. Those splined triangles at the top are rotors. My engine has two of them. Some RX-7s have three. The old RX-3 had one. Each rotor spins and travels through a chamber shaped like an "8". There is very little lost energy in a rotary engine, while a piston/cylinder engine has a comparatively large amount of wasted energy--the pistons must travel up and down, therefore having to stop and reverse direction many times a second. The RX-7, no longer sold in the US, is the only car on the road with a rotary engine, also known as a Wankel, after Felix Wankel, who invented it. The advantages of rotary engines over standard piston engines include high power in a compact, small design, amazing smoothness, high resistance to damage caused by over-revving, and reliability. The drawbacks: high temperature, high noise level, high fuel consumption, unclean emissions. As a rotor spins and moves, a continuous cycle of intake, compression, combustion, and exhaust enabled by the inherent shape and design of the rotor and its chambers takes place which mimics the stages involved in a standard 4 stroke engine. My dual rotor 13B rotary engine uses 4 spark plugs. Rotary engines go through oil roughly five times faster than the average 4 cylinder engine. Early RX-7 TV ads featured the concept that a rotary engine just hums as RPMs increase, in opposition to a piston engine which as said, wastes more and more energy as RPMs increase. Finding a mechanic who can work on rotaries can be a difficult endeavour. I recommend everyone go out and buy a rotary engine.