Yes I agree Attak man that the 4 strokes are always going to be heavier. Too many hard/heavy parts in a valve train. No way around it. But if the chassis and engine are both designed together from the start, you get a better balance/ handling sled (CG). I have rode the Vector, Apex, and Vipers. I have not rode a SideWinder as I don't need that kind of power. Yami engines are very good, no dought about it. But even the Yami/Cats, (Viper/AC7000's) do not come close to the balance/ handling of the Doo 4 stroke sleds. This is why I have had hopes that Yami would come with a chassis/ engine designed together that would accomplish the balance/handling. I don't want a snowmobile that needs power steering, and it doesn't appear very many others do either.