RE: What is the max prop RPM?
If a .21 car engine is set up to provide max RPM's as this one appears to be then you'll want to run it with a rather small prop. SOmething like 8x4 to 8x5 at most. The hot FAI .15's run with a 7 x 3.5'ish prop to reach the high 20's to low 30's that they run at.