Thanks for the reply's, gotta love RCU. I am converting two twin ring Ryobi's for a B25 I am building. Got one of them partialy converted last night. Got impatient and did not even take it to a machine shop to have the fly wheel turned. Found a old prop shaft adapter left everything stock, muffler etc. Put a 16 x 10 zinger (that I hate) and got 6700 rpms. Put a 17 x 8 apc and got 7200 rpms. Not too bad for the stock muffler and only 15 minutes on the motor (brand new) I hope to get another 300 - 400 rpms with a new muffler or gut this one. It will be interesting to see if removing most of the flwheel fins will attain more rpms.

Peter