I have a YS .91 AC mounted inverted. Keep in mind that a heavy engine will require lots of tailweight to balance as I found out with the YS. This combo is fast though, with a 14X10 apc it goes. Mine flies like it were on rails, but does not slow easily, I have to make a long aproach on landing. A friend powered his with a .61FX with a 12X6 prop and did not have this problem.