RE: Q 500 - os 46df engine
The DF engine is timed for higher rpm so most people have gone with a 7.4x7.5 CF Q40 prop. The props you have are too much load for that engine to run where it should. That brings up problem #2. A 7.4 prop really isn't suited for a Q-500 airframe. It has been done with fair results so at this point I would continue.