I used the OS46ax on mine and it's fine. However I did still needed quite a bit of weight for the nose. I have a 2400mah 4cell just aft of the nose gear former. I had thought about an OS61 for more power, I only used the 46 because I had it. I put a 10x8 pusher on the engine because that's what I could find. A 10x7 would be better or a little more power on the 10x8 would probably be just right. If I installed a slightly heavier engine like the 61 I could still move the battery forward of the former and get it to balance. The 46 moves it at 75 to 80mph not bad really. I toyed with the idea of a Wren44 which is only 6oz heavier than the OS46 (believe it or not) but this plane is really geared and designed for a 40 -60 pusher prop engine. As far as adding weight I believe it could handle an extra pound no problem. mine is 7.5lbs the landings are a breeze. Someone in the post was worried about getting the wing loading to high well, if this is a stepping stone for you (or anyone) into DF or turbine jets, your next step is sure to put you into a more heavily wing loaded plane anyway, might as well get used to it at $250 total instead of $5000.