I have flown mine with OS 70 and 52 four strokes. I like the 52 better as I did not have to add any weight. With the 70 I had to add about 6-8 ounces on the tail if I remember correctly. With the 70some creative installation work had to be done to get the throttle servo to work out, also.Whatever you decide to use, the Kaos is simple, reliable, dependable and predicitable and you will enjoy it. Good luck