David the 61 Comp seems to like the APC 12x10 when using no or low nitro giving around 11300 rpms. The 80 comp I'm using a APC 12.5x13 turning 10k. so far on 5% nitro. The engine has unknown hours on it. Right now I have it torn down getting some cylinder work done on it. Also putting new bearings while I have it apart.