Well, you can start [link=http://www.osengines.com/manuals/fs-120s-iii-manual.pdf]here[/link], that's the manual. I run a 16x6 and a 15x10 on mine, but they're on war birds. On the Funtana, I'd try a 15x4W. With the 16x6, I get about 8700 RPM on SIG 15% fuel. I tried running some 30% with a #8 glow plug, but I get more RPMs with the 15%. That's enough to get a 13 pound P51 off the ground. Once the plane is in the air, there's alot less resistance on the prop. I can hear it turnung faster than it did on the ground. I even traded props, and the non pumped 120 performed almost identically.