More Horsepower !

Pat McPherson · 10-04-2003, 09:52 AM

Well I thought I could hold off talking about this subject until the season was over, but....

How much faster will I go with another 50 or 60 horsepower in my 1997 24ft?

With my 310HP/7.4MPI she runs pretty good. About 65mph GPS, 68 on the speedo with a normal load and a 4blade. The best I have seen is 67.6mph GPS and 71 on the speedo with a light load and a 3blade.

I have done quite a bit of research on potential mods for my little 7.4MPI.
My plan at this point is to bolt on another set of stock heads that have been bowel ported and have had new valves and springs installed.
I am going to change out the stock cam for a mild performance cam.
Bolt on the Stainless Marine exhaust that I never got around to this year.
Then have AZ Speed and Marine recalibrate my ECU.
Desk Top Dyno says that I will have about 400HP with my combo, but the experts have told me the MPI will only flow enough for 375HP at 4800rpm.
I guess if I want a little more, the MPI will have to come off to extract another 25HP at +200rpm.

Dave M · 10-06-2003, 06:27 AM

It will be interesting to see your results. You will have about the same HP as me. We will see what, if any difference the step hull makes. I think with 400 HP you should be at around 76 GPS. With 375 you should be at 74.

Pat McPherson · 10-07-2003, 12:37 PM

Hey Dave,

I think the 385HP is a conservative rating on your engine. I believe that your engine is a marine version of a Gen. VI 454HO that is rated 425 at the crank.

There is a Superboat owner in upstate NY, Gary is his name, that modified his 454mag. He had his engine dyno tested before and after. I looked at the paperwork he sent me, 420HP at 5200 before, 500HP at 5600rpm after modifications.
Gary's boat is a 1996 conventional V and runs in the mid 80's with the 500HP engine

I think that the drive only eats about 20hp, so you probably have more like 400hp at the prop.

Dave, I hope that you are right and I will see 74, but I am thinking that I will end up at about 70mph. Right in the middle of were it runs now and how fast your boat goes.