The Pitts muffler I use is the one sold by RCShowcase It is a Supersonic
the setup was new -engine propmuffler -I simply bolted it all together - added 32-1 Mobil with pump gas (91) and on first tank cool , the engine turned almost 7100 then loosened up easily 7200 .that is on the ZM 26x10!!- the other 26x10 's turned mid 6000.
Bambula and menzS
all mufflers are not the same just like pipes or cans the differences can be huge.