Ditto on the OS. On my 3lbs competition fun fly I use a Irvine .39 with a Yusa tuned pipe. A throttle pipe is usually better for these. Or if you plan on using a Irvine .39 you will be better off with the proper Irvine pipe made for the motor. Other option which is not listed is the West .36 with the throttle pipe. Very powerfull and very light motor.