One of the biggest problem we have seen out of the evo engines is the crank pin breaking.

PROP we get 17,800-18,000 on APC 9x8 props for the OS 46's on jett mufflers
PROP we get 14,500-14,900 on APC 11x7 props on the OS 55's with jett mufflers
PROP we get 17,300 on 9x8 APC for the OS 37 with jett mufflers


For your 60NX check exhaust timing and get it to 180. If it isnt there then put a 15 degree upwards angle on it till get to 177, this with the upward angle will get you to 180. As cox said make sure compression is correct for the fuel you use. As a reference my Jett 60 LX only spins a APC 9x8 at 18,400 on the ground.