I flew Gremlins for 10 years(and still do)with OS.40fp's on them and it seems to be the best engine/power for that plane. They don't make the FP engines anymore but the TT.42gp is a clone of the old FP's. I find the bearing .40 sized engines are too heavy for that plane and take away too much of it's agility. I LOVE those Gremlins !