When you have a 3:1 or better power-to-weight ratio, the number of strokes it takes for a combustion cycle doesn't matter. When they start them up, they pick the chubbiest guy they can find to hold it down. 90+lb of thrust in a 32lb plane... Outrageous to the extreme. Really, what would be the advantage of a 100+cc 4-stroke gas engine in a TOC plane? It's more complicated, heavier, etc..