[quote]ORIGINAL: ckangaroo70

Quote-but 1/5 scale might be a little better choice and offer the abillity to maybe even do a few simple aerobatics especially in the clipped wing version-Quote

I have the 1/5 scale Cub, and at ten pounds flying weight, a .65 is plenty. If you were to clip the wings and make basic aerobat out of it, a .72 would still be plenty. I think you'd be "throwing away" a good engine to put a .91 in a 1/5 scale Cub.

Sig recommends a .90 to 1.60 4-stroke for its clipped wing version of the J-3. If you built the full span, you would get more than adequate performance from a .91, and even the clipped wing would fly fine, although you'd be on the lower end of the power loading spectrum, and vertical performance would be limited.