I never even considered a Pitts type muffler for mine - - but I know others may want that setup .
I think it is a good engine - I saw other engines on the same muffler and they also were down on power - but quiet.
Jim Bisson makes a nice product and he has no illusions about the way you control noise .
I see -tho -- many "flyers" who think that all mufflers are basically the same - -- not so .
The only "poor"comments I have seen on the engines' performance are from those using a restrictive setup -
I have checked two o fthese -flying H9 80 " Caps - all stock -on stock Bisson Pitts and Bambula 20x10 props .
these both turned 6900 here at 4500 ft elev.
The Caps both have fully unlimited power .
my 40 on a tuned can - 6800. Bambula 20x10-