depends on what you want

scale fun fly: Magnum 70
quick and nimble: Y.S. 63 or Saito 82
heavy and fast: Magnum 91

naturally the Magnum engines are the bang for the buck engines. the TT 91 is also good.

i've had friends with the FS52, the 70 Ultimate (kept losing his muffler :-), FS70 and the a bunch with O.S. Saito and Magnum 91s. the 52 is a poser... a little too light for this. a 70 is minimum i think. the 70 Ultimate was powerful but needed some weight to balance. the 91's were all great but each of them reinforced the wing because they all like to the scrafing runs pull up to vertical, roll and 3/4 loop back down to another. they do this in succession until they have to land. it's fun to watch a bunch of WWII planes (axis and allies) up and down the runway but no one will fly when they do this because we all know how dangerous it could be. btw, of all the planes i mentioned, only two have the dago red version. everyone else runs the standard p-51.