ORIGINAL: Flyer95
This engine responds good to a tuned pipe. My ST90 on a tuned pipe turns a APC 15x6@10000, APC 15x4W@12000 and APC 13x8@12000rpm. I am currently running a Master Airscrew 16x7 to keep the rpm & noise down
The 15x6 and 13x8 should be much closer in RPM -- the load in not that far off.