Like cben said, they are for two stroke motors. Don't know the difference so all I can do is speculate.
Two strokes spin double as fast as 4 strokes so they should flow double also, although there exhausts are tuned so the backpressure works with the expansion chamber.
Two stroke exhaust has a higher pitch than 4 strokes so they should be tuned to reduce higher frequencies better than the 4st rumble.
If you install them let us know how they work cause they sure look trick.