TT 2-strokes are the posterity of Magnum copies of OS 2-strokes in the 90's.

TT 4-strokes, however, are original design. I've heard of a few problems with the TT .91 4-stroke, particularly with the carb design. My friend can't get his to run right.

I would recommend the Magnum 91, because of the cost. It's plenty strong for a 4*60. If it were an aerobatic or 3D plane, I'd go with Saito or YS.