I dont have a lot of experience with 4 strokes but a think a 40 - 45 size 2 stoke would out perform my 50 saito that I have on my cub. I really want a four stroker on this agwagon. My old saito sounds, runs, and idles great. It never fails. I just want to make sure I get enough engine so it is not under powered but at the same time I dont want to over do it. Also, what would be the possibility of a smoke system? This plane is supposed to weigh 6lbs and has a wingspan of 69". A 40 - 46 2 stroke is recomended. All help is greatly appreciated.