It HAS been answered but I'll do it again.

I built and flew one with a Brison 2.4. It was not real heavy at 12.5 lbs, flew great, but one must be careful about applying full power all at one time, there is a pretty sizable torque reaction if you just slam the throttle open at low/no airspeed that could get you into trouble.

That's the story. I would not go bigger than the 2.4.

TF