I have tried a 14X6MA and APC and a 13X6 APC. Dont remember off hand what they tach at. The engine runs well with all of those props and I do remember a boost in performance I just dont remember how much. I´ll tach it next time I run the engine. With all of those props I am sure it is staying in the 10 to 13K range.

Bob, will that muffler fit the new OS120?