I was using the 12 as an example, but I understand your point. I have a 16x8 on it now and it will pull my 62 inch span SU-26 straight up all day long. I think I am going to work up a way to measure actual pull the plane (prop/engine) develops in pounds. I had this engine turning a 14x8 master airscrew at 13,600 rpm on a stand with 15% powermaster fuel, and the sleeve was still in the carb. I am planning to use an 18x4 for 3D after I get the initial few test flights worked out. So the HP cant be far off.