There are 2 40s out there the Q40 which is the same as the diesel except for the head and the regular 40 I assume yours has the bolt
on front they will run fine on 5% nitro 10x6,7,8, or 11x6,11x7, 12x5 (source irvine data sheet that came with engine dated august 1993
rpm 10000 to 17000 per sheet I would not consider running over 12000 they have gobs of torque and would consider running the 11 or 12 inch props to use it, I have both engines beside the new MRK lll red ones their best feature on all is the irvine jetstream carb one of the best. If you need a head shoot me an email all mine are converted to diesel so I do not need the glow heads