How fast can a 75 HP motor go?

There is no direct correlation between horse power and speed. That is to say you can't put an exact number because of all the other variables. I have seen a car with about 75 hp do well over 150 mph and my farm tractor with 72 hp only has a top speed of 30 mph. There is an old saying "how fast something will go depends on how much money you want to spend".