OK Gentlemen: I drilled a 1/2 inch at the stock muffler and RpM's went up to 6,500 with same 17X8 prop. I have ran 3 tanks for breaking
and next step is to test with a larger carb. The plane I'm planning to put this engine on is a heavy Katana and I believe a smaller prop will not do a good job, so I need at least 7,800 rpm. Will see what is achieved. Thanks to all of you that gave ideas and suggestions.