Shoot over to how stuff works and look at two-stroke engines to understand how two-stroke engines work (nitro engines are mostly two-stroke engines)

Pipes: Pipes affect the back pressure, and because of the dynamics of the exploding fuel and the need for the engine to clear out the gases, pipes that can do this at different rates and efficiencies can affect how the engine runs. Some pipes allow the engine to exhaust gases very quickly and this can create a situation that lets andengine rev very high, or the pipe can act in a way that it slows the process down and makes the engine happier at low RPM. You are getting very advanced when you start discussing the physics here, so don't get ahead of yourself.