i have a 10' GW invader, and i have a 1968 40hp johnson on it, and it goes 47 km/h. which isnt too bad, but last year i was running a 1955 25 johnson and got 46km/h, so there must be somthing wrong. and i was reading about someone with the same boat and a 50hp, and the boat goes 90 km/h. it...