Ernie yes, yes, sometimes. first off most 3d planes need large props with large low rpm engines. yes you can hover some planes with a glow two stroke but need a large one. Second this is a P7 its in the BPA/SPA range in speed so the Jett muffler fits in here well. no if going to compete and the rules say no "Jett" muffler as some of the rules do. So yes those rpms do help on uplines and so forth. now if want to fly this plane in a sport manner and dont care if not flying fast as most then sure you dont need the Jett muffler. I fly everything from fast planes to slow one. I am working on a Piece O' Cake right now. top speed 35mph lol

Duck has already ordered the Blue muffler.