True, maybe more horsepower, but the horsepower specs provided by manufacturers are rarely real life figures, they are the best specs that they can manage to squeeze from their engine in a lab(Big HP=Better Marketing). Also the tuned pipe adds quite a bit of punch to the 2-stroke engine. And 1 further point, since we are talking top speed, how many Pylon Racers do you see running a 4-stroke? The higher rpm of the 2 stroke will allow you more top end. The 4-stoke might be able to pull you vertical forever, but for pure speed, your going to want a high pitch, high rpm, prop.