Here are a couple of different sources for recommended R.P.M. ranges for the YS-63.

http://www.ysperformance.com/prod63.htm

http://www.centralhobbies.com/Engines/YS63FZ.html

The engines do like the revs. I prop my YS-53 to turn around 10,500. I will be installing a 63 in a new plane shortly, and plan on doing the same with it.

Outstanding engines!

Hope this helps.

Rex Rutledge