Wankel

In 1969, Mercedes-Benz unveiled a concept car powered by a Wankel rotary engine: the C 111. Built as a test bed for the unusual engine, the first version of the C 111 had a three-rotor unit with an output of 280hp and a maximum top speed of 161 mph.

One of the coolest things that Mazda ever did (other than the Miata) is produce its high-revving Wankel rotary engines. That engine powered Mazda RX sports cars going back generations. Word has surfaced from Mazda head Masamichi Kogai that the company still has a team working on improving the Wankel engine.