Tim;
The YS 63 is one of the most powerful or is the most powerful in it's class. I run a 12 X 7 APC and it already turn's in excess of 12+K. a 13 X 6 APC turn's in excess of 11K. To put a smaller prop on a 63 is just nut's. Adjust prop size accordingly and use throttle management. Dave your absolutely correct there is no better in any class this is most reliable I've seen.