Originally posted by jharkin
A tuned pipe wont do anything for a 4 stroke. They give 2 strokes a boost because they create a resonant back pressure wave which actually forces some of the exhaust mixture back into the cylinder for a supercharging effect. This works on a 2 stroke because the overlap in intake and exhaust port opening timing can let some of the unburned fuel/air to go out the exhaust.
-Jeremy
Actually a tuned pipe will boost 4 stroke engines to a much smaller degree (than a two stroke). Not nearly as much as tipping the can (of nitro).
There have been some racing with 4 stroke engines, but I think mods were mostly reducing compression, adding nitro, removing the muffler or using a less restrictive muffler, putting a shorter higher pitch prop on, and letting it rev well past the manufacture's recommendation.