I had the OS 1.60 in mine and it flew it very well. I have since traded the bipe for a Creek Staudacher that I hope to have in the air next weekend. The only prop I tried on the engine was a Zniger 18x6 which I've read it the worst prop for this engine. But even at 8100 rpm, it would take the Ultimate straight up from takeoff and go as long as you wanted it to. The OS is a great running engine and a good combo for the plane.