Fox says 5% nitro and 20% castor oil and recommended 9x5 prop in their paperwork. I remember Malvin at Fox saying 15% nitro was preferred for the best performance. I have the older 25 bushing version on a Flight Streak and run 5% and 25% castor, 9x6 and factory muff. Its a tad fast with 6" pitch...but is a sweet runner.