I have a friend that built the Hog bipe and put an OS 91 four stroke in it. Because he is still on a trainer, I get to fly his other stuff, like the Hog bipe. In my opinion, it has enough power for what the plane was designed to do. If he had built it a bit lighter, it would be that much nicer. If you are worried about weight and want more power, look into the YS 110. What I am doing on my 120 sized planes is going to a bigger prop / less pitch. On my QQ Yak with a YS 140 L, I am running an 18x6W. I have the power I want where I want it.

Dan