What is faster a piston engine or rotary engine?

Answer 1

There isn't one that is "faster" and it depends on you're definition. Engine speed and the car's speed both can be defined as how "fast" it is. I'll try to answer for both cases.

If you mean engine speed (rpm), then yes and no. They typically are able to turn over at a much faster rate than piston engines because the inertia is evenly distributed into a circular pattern in the triangular rotors. In a piston engine the center of rotation is not the center of gravity (those points are one and the same in a rotary) and therefore centripetal force is unevenly applied to the cars internals. This makes high engine speed very tedious and expensive work (ie Honda S2000, BMW m3, Lexus lfa, etc) or failure will occur. Rotary engines on the other hand can be made to operate at high engine speeds without much extra in terms of cost. They do have limitations however. Heat distribution and complexity for basic repairs are two big ones. You can find more with a quick Google search.

If you meant overall speed of the car, there is no way to tell. The size of the engine, size of the car, aerodynamics, etc would dictate things as well as the simple difference in engine type. Rotaries do produce a higher amount of power per liter in almost all cases over piston driven engines, however.

Hope that helps!