I know that optimal power would be a moki 2.10 for 3D but you would drink alot of glow fuel. So then you go to gas, you will probably get alot of people telling you that a G45 is no good, to heavy bla, bla bla. Yes a G45 is 9 to 12 ounces heavier then a 40 or 50cc engine but everything I have read says it will pull it nicely. The question you have to ask is do I want to do wild 3D? Do I want to use this plane in the advanced and unlimited class of IMAC? If no then a G45 would be a trouble free nice engine. If you awnsered yes to any of those questions then you should get a performace engine in the 50 to 52cc range(BME, DA, Taurus, 3W, ZDZ, Brison, FPE, Fox, ect.) I am going to be flying the Intermediate class in IMAC this year and that class doesnt have any vertical snaps or other manuvers that would take a ton of power. So I am going to put my ZDZ 40 in it and have fun. I hope this helps