I agree with Raideron. I am currently using an APC 16.5 X 5W on my YS 110 FZ and both it and the 17 X 4W seem to rev and pull equally well. As Raideron said you gotta watch the wide open throttle with the 17 X 4W - - the 16.5 X 5W seems to load it up a little more alll over the powerband and the prop doesn't "rip" quite as bad as the 17 X 4W at speed.

TJ