That sounds like too much prop for 0% nitro. If nitro fuel is not available, I would try a 10X6 prop. I doubt you're turning even 10K RPM. I will be using a 10X6 or 10X7 with 15% nitro on a Jett FIRE .50 engine & tuned pipe. This combo will turn 15K to 16K RPM which should be plenty of pulling power.