I suspect a 12x8 three blade would be about right, Graupner and MA and Zinger all make then. I use three bladers almost exclusively, so I have them from .15 siezed engines to a SuperTigre 4500, I'm converting the 4500 to Diesel operation so I'll need a bigger one yet. In the neighborhood of a 20x10 three blade. Something to keep it in the 7,500 rpm range.