Thanks for the info - that looks about right - 500 rpm gain is a pretty significant HP gain when dealing with a 14" prop.

If the opportunity arrises, try an APC 15x6 too. Might surprise ya

Technically the muffler will work on the OS120. Just matching up the bolt pattern is the key here. Im not sure if either sets of fastern holes on the muffler match the OS120.

I do know that Dub has an OS120 for testing, but he has been busy on a couple of other projects... not sure how much test data he has so far.