RE: pitts muffler changing performance
alexcc, I've got/had several pitts mufflers on various engines. If all is set up properly you will not experience any negative effects to the motor. I don't know if the pitts mugfflers are any noisier or quieter but can give a pretty nice sound. If yours is a bolt on as opposed to strap, make sure to clean the bolts with acetone or rubbing alchohol and Loc Tite when you install muffler. Have had a couple come loose on me, causin dead sticks with adverse results. Good luck.