You are correct on the supercharged 4 stroke Kuma. YS/Futaba makes the only supercharged 4 strokes on the model market. These engines are phenominal powerplants, bat are for airplanes. They use the crank case as the air pump and essentially put twice the fuel/air mix in the chamber as a normal 4 stroke.

As a point of reference, I used to fly a plane with one of their .91AC engines on it. A normal .91 4 stroke normally turns a 12x10 prop (diameter x blade pitch) at 10K rpm. My .91AC turned a 13.5x12.5 prop at 10K.

It'd be cool if YS made a 4 stroke car engine, but they don't.