Hi All ... Ok, I have spent better than 30 years designing and bui;ding controlline stunt airplanes. Now it is time to move up into the world of R/C. Recently I have seen some pretty impressive 4-stroke engines preform. Since my prior experience is with 2 strokes ... WHAT IS THE CONVERSION BETWEEN 2 AND 4 STROKE MOTORS?? That is to say .. .if I have a 35 - 40 - 50 or 60 size 2 stroke plane ... what size 4 stroke should I be looking to buy?

Also .. who is the "top dog" in four stroke engines ... Saito? OS? Magnum?

A lot depends on the type of plane, and the performance you want. For example, a "40 Size" Piper Cub will fly nicely with a .52 4-stroke. But if you want you Cub to do some nice "Clipped Wing" aerobatics, a 70ish 4-stroke would be better.

For MY personal taste:

.46 2-stroke = .70 4-stroke

.60 2-stroke = 90ish 4-stroke

Generally, add 50% to the two-stroke displacement to get the four-stroke equivalent. So MinnFlyer's recommendations are fine. My only 4S experience is through other flyers. At our field, YS engines rule.