Most cars you see on the road have a traditional piston engine under the hood. However, a few models may offer a distinct difference with a pistonless rotary engine or rotor engine. Instead of pistons, they have rotors.

Fewer parts that move

A rotor engine doesn’t have as many moving components as you see with the piston engine. Just think of all of the components on a piston engine. You have the connecting rods, camshaft, valves, rockers, timing belt, timing gears, crankshaft and of course, the pistons. Even the simplest engine will have at least 40 parts.

A rotary engine has just three moving parts with the two-rotor engine. Two of them are the rotors with the third being the output shaft. Because of the fewer moving parts, there is greater reliability from the engine.

Smoother motion

Parts in a traditional piston engine change directions as they rotate, while those in a rotary engine move in the same direction. They also feature counterweights that eliminate vibrations which occur in piston engines.

The rotor engine is also smoother than a piston one. It has three revolutions on the output shaft for one revolution of the rotor. For the piston engine, the combustion happens on every two revolutions and a quarter of each crankshaft revolution. The rotors on the rotary engine move slower than on a piston engine, which improves reliability.

Rotary engines are not seen in many vehicles, especially those in the U.S. because of emissions. However, Mazda has had a great deal of success with the Wankel engine, which is a type of rotary engine, used with racing cars.

This article originally appeared on YourMechanic.com as How Do Rotor Engines Differ From Regular Engines? and was authored by Joyce Morse.


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