there is no power gain between fiber glass,steel wool, empty or no silecer at all(does not harm the motor!!!only your ears,LOL)...your silencer is just that(a silencer) its a strait through tube with no wind resistance=no backpressure;that means no power change only sound absorbtion...and the only time you get a power gain is from switching to aftermarket from factory(factory MUFFLERS have baffles and or packing)they do have wind resistance and will cause backpressure thus reducing power. the time a two stroke NEEDS bakpressure is when the exhaust pulse is in the expantion-chamber, making the pulse travel back and fourth acting as the exhaust valve.