totally agree...the quiet muffler and pitch of the prop at certain degrees of no-power dives will make the powerplant stealthy I'd be surprised if you wouldn't see a 600-800rpm increase in RPM by changing the muffler to something more free flowing (but loud), like the AbellRC muffler. The Slimline pitts is a good balance between RPM gain and sound if you'd like a more balanced upgrade. Just remember to retune with any prop/muffler/oil changes you employ!

Chad