I posted this somewhere else, but its pretty impressive for a Chainsaw engine, Homelite 55cc out of a 330 Model Saw. I have 30 bucks and some fab time invested--Runs as well as my G-62, at least on the bench:

Zinger 22x10------------------6800rpm
Master Airscrew 20x10------- 7600rpm

This is at 900ft elevation, about 50-55 degrees. Actual in the air trials will have to wait for warm weather--plan to install in a Giant scale (92"ws) BT-13.