A 4 stroke makes a power stroke on every 4th stroke, whereas a 2 stroke makes one every 2nd. That is why the horsepower of a 4 stroke is less than the same displacement 2 stroke. It would need a 4 stroke of approx 1500-1600cc to have the same stock hp as a 1000 2 stroke. The 4 strokes at around 12 psi are also running 91 octane and not rebuilding at the same frequency as the 2 strokes. There also seem to be a much higher percentage of them running successfully.