I had a magnum 52 four stroke on my 4*40 last summer (first summer flying ) and it flew fine, albeit a little slow. I ended up pretty much flying full throttle the whole time doing low flybyes with a grin on my face. I've since decided to up the engine size so I put a Thunder Tiger .65 (GP61) 2-stroke that I had laying around [>:]....Ought to be a blast.