has anyone used one of these thrust chambers? http://powroll.com/P_HONDA_XR50.htm . I know making a silencer longer would give you more back pressure but i dont know if it is the same way with four strokes.
"Powroll muffler spacer alone: Useless, does nothing. If it wasn't included in the big bore kit I wouldn't have it. It does look cool though. I had it on before I installed the big bore and noticed no change."