I just did some testing on my ryobi 33 cc weedwacker engine and with a bigger carb, wackerengines pitts muffler and an electronic ignition it spins a xoar 18x8 to 7250 rpm this is a pretty agressive prop. My motor also has a two ring piston and the cyliders without the decompression slots. No porting has been done. just using the best parts combo.

Chris