GPSpacewalker, you are right, in motorcycles 4 strokes are allowed to race an engine almost twice the size of the 2 stroke. 450cc vs. 250cc. This rule was allowed by the rulemakers because just five years ago there were no 4 stroke motorcycles that were competetive. Now the 4 strokes have almost taken over. So, for now at least the 4 stroke seems to need a displacement advantage to make similar peak horsepower. However that is changing very quickly. Even with similar displacement, the 4 stroke favors a wide, wide powerband. Much wider, perhaps 2 times as wide as the 2 stroke. In many applications the powerband width is more favorable that overall peak horsepower. This seems to be the case in airplane engines. The 4 stroke will spin that bigger prop quicker and gives that instant power and over a mid RPM to peak RPM that the 3D pilot seems to like. And some manufacturers (YS) don't seem to have a power disadvantage at all. YS 160 DZ engine seems to put out just as much as the OS 160, and still has that great 4 stroke feel. Also, it was mentioned that the larger airplanes seem to favor gas 2 strokes. That is true but I read about a manufacturer that is making a 4 stroke gas engine for planes. It was a small one. But it is just the start and we can look forward to 4 stroke domination in that area as well in a few years.
Thanks,
Barry