ORIGINAL: Airplanes400
ORIGINAL: MinnFlyer
A lot depends on the specific engine, but I generally say:
40 - 46 (2-stroke) = 52 - 70 (4-stroke)
55 - 65 = 91 - 100
75 - 90 = 110 -125
Larger than that, Gasoline
I agree with the above with the exception of a .52 4-stroke engine. I'd equate them to a 25 to 32 sized two-stroke engine. I have always used .70 4-strokes in place of a .46 2-stroke.
There was a time I would have agreed with you, but I've got an OS 52 which I have used in several 40 size planes that was MORE than enough power!