It depends on the brand of Stik. Great Planes Stiks have a generous wing area, and I have put 20 to 25cc engines on the .60 size numerous times with very good results. You may have to move the servos to the tail if your engine is heavy and/or it has a magneto.

I generally figure about a 1000 square inch wing to be about the minimum (plus or minus a bit) for gas engines.

AV8TOR