Performance Question

[Aceman]

Given a light wieght flats skiff with a 2005 40 hp Yamaha 2 cycle will top out at 34 mph on gps.
What would the identical boat top out at with a 2005 Yamaha 50 hp 2 cycle?
Please note both engines are identical weight.

How about with a Yamaha 40 hp 4 cycle weighing 8 lbs more?

[Ken]

Ace,
My gut feel says with ten more hp, you might get up to 40 top end.
The same hp in a 4-stroke and 8 lbs heavier
(only 8 lbs?) will give you same top end, maybe one mph less, but much better fuel economy.
Good luck,
Ken K