I built a cheap 20" ABS mono with one of these jets and at 17 turn (I think) car motor, 6 cells and was incredibly slow, like walking pace, and that motor would have higher revs than a 600. It was probably mainly because of the hull size, but I think the jet was also fairly inefficient, as there was alot of friction in the driveshaft, and the impeller wasn't vey well designed.