Hello Jim!!! I put the 11x6 on the plane(4*40) to actually slow it down a litte on landing. I did not try a 10x6 or 10x7 on it altho it would probally turn a little more rpm with these 2 props. This was with omega pink 10%.Alot of people use the 10 inch props with good results. I now have this engine on a Modeltech Me 109 arf without the header due to fuse restrictions. I did drill out the stock muffler exhaust a little.But with the header/moussecan setup, it was like a whole new engine- idle was dead slow and response was instantaneous!You could actually hear it come onto the pipe when you opened her up!I used a OS #3 plug if I remember right. Your 13,500 rpm sounds about right for stock setup. Happy flying!!
John McGowan, Birmingham, Ala