The os 70 is a great engine , have not owned one ,but, everyone I have seen is a great runner. Myself, I have a habit of overpowering, if I was going with the wieght of the 70 I would install the saito .91 instead. Put one on a Skytiger and it turned it into a animal. It's all what you are after. My vote would be the Saito 91. Easy to pull back the throttle,tougher to crank power out of a engine when it is'nt there.