A Magnum 80 or 91 would be good. The 91 would give you better vertical, but might be a little much. TT only makes a 91 sized four stroke that would fit this plane. Well, they make a 54 too, but it would be way to small.

The Saito 72 is a good one. They also make an 80, and I think it is just a bored out 72.

the .72 is a bored out .56. The .80 has a different head and thus weighs more. The .91 is a bored out .80. The 100 is a new engine all together but weight was a strong consideration in its design.
PT

I have the same plane and am consiering a 52or 54 4 stroke. The hooby dealer I bought it from built one and installed a YS63. He said it was WAY overpowered.[img]i/expressions/face-icon-small-cool.gif[/img][img]i/expressions/face-icon-small-frown.gif[/img][img]i/expressions/face-icon-small-confused.gif[/img][img]i/expressions/face-icon-small-frown.gif[/img][img]i/expressions/face-icon-small-cool.gif[/img][img]i/expressions/face-icon-small-tongue.gif[/img][img]i/expressions/face-icon-small-shocked.gif[/img][img]i/expressions/face-icon-small-mad.gif[/img][img]i/expressions/face-icon-small-shocked.gif[/img][img]i/expressions/face-icon-small-tongue.gif[/img][img]i/expressions/face-icon-small-cool.gif[/img]

We've been flyng one with a Webra .50. Balanced with no extra weight. Excellent combination.