RE: Jett Stream muffler question
not to worry.......
the port size does not matter. Hundreds of them out running on TT, OS, ST .... about all engines, no issues.
Bolt it on, and run it. Try to target 16,000 rpm or higher with your prop selection. A 9x7 is a good place to start.
Set the needle about 600-800 rpm off of ground peak for flight.
Bob