I have a 1991 260 with a 330hp 454, top speed is 55 to 58 mph depending on weight. I am consideringincreasing the horespower to somwhere between 450 and 500hp. I am wondering what kind of top speed I can expect, and how the boat cruises. currently the boat cruises at 36 to 40 mph @ 3500 RPM.

I say 8-10 mph on top

I think thats about right too. I have pretty much the same boat (250ES) and have been considering the same thing. My current speed is about the same as yours with a 21p. I'm looking at 500hp with the correct prop and hoping to get close to 70

it was a quick cruize but 70 on the water is the biggest rush.... well, ill be saying that about 80 next and so on.

i am hanging my head out the car window at 80 trying to get the feeling on my face from that day, you know all the blood rushing back in afterward.

HammerHead,
I have a 1991 260 Baja with a 509, 563 hp dyno'd at crank.
email me at [email protected] & I can give you more information about speed gains compared to hp
Gerry