Update
Bought an apc12x12 yesterday, and flew it today. My YS91AC turned the apc12x12 at 9700 on the ground. It didn't seem as fast in the air, but I feel better (engine health wise) with this prop. With the 12x12 it may unload to 10700 - 11k in the air, with the 11x12 it may unload to 12300 - 12500 in the air, or what do you think. When does valve float start taking place in a YS91AC, and how big is the chance of valves hitting piston top, or other internal no nos?
DKjens