I have heard of people doing a small amount of grinding on the exhaust port, mind you - I mean a very small amount. And some put different carbs on with a bigger throat and loose the stock muffler. I seem to recall someone getting around 7700 with these upgrads but that was quite awhile back. Somebody else might know better. Performance isnt this engines strong suite. Its like I've heard a US41 described, its a good airplane truck engine.<g> I was never able to hand start mine. I used a regular sullivan dynatron. The thing to remember is that the crank counter balance is three rivited stamped plates. Just my opinion, not really ment for very high rpm's. But up to 8000 or so should be ok. Mine was more than acceptable in the plane I used. Want to do a ryobi twin someday.
Edwin