Two-stroke or four stroke, the choice is yours. I'm a 4-stroke fan myself, except for my trainer all I have is 4-strokes. Personally, I think a Cub begs for a 4-stroke. A .56 is adequate for scale flight, but a .65 or .72 gives you some reserve power, plus allows you to just putt around at low throttle settings. I have the 1/5 sig, love it, and have a .65 Saito in it. A .46 2-stroke will fly it, but I think you will be wanting a little more oomph after you've flown it a while with the smaller engine. Just my $.02.