IMO the headers are doing very little on a procharged engine. Have you checked your air/fuel ratios? If you're running pig rich you can knock down the hp. Adding 200hp is possible if set-up correctly, if not that 675hp estimate can easily become 575hp.

I think you may be reaching a bit expecting a 200hp gain on that setup. Unless you have dyno numbers, I don't think you can pull the ricer move and add up some advertised numbers and believe you're at 675.

Call mark at precision marine and question him. Hes the best as far as you so called experts on here say. He tuned it. So ya its set up rt. Plugs are perfect. Its not rich. And not too lean. And 575 isnt going to slip a 30p b1 and a 29p hydro p5 at thoes %s. And hell if anyone wants to trade me a stock set of manifolds for my $4000 CMIs lets do it since thats whats slowing me down. LMFAO. do you guys read this **** before you post it? Seriously? Im trying to fig out why my PROPS are not hooking up. The power is there. Its not a hp issue. Its a prop slip issue. Do you think you blow the tires off on a drag car becauae you dont have enough power? F@#k no. Its because you got too much power for whats under the ass.

In my opinion the problem is that i have one of the biggest single engine boats made. And it has THE biggest step hull of any single engine boat made. The prop is turning in the bubbles the step is making and we all know that props arent made to push air. Its obviously a boat/drive setup issue..... and juat to add to this. This setup im running has a hole shot like ive never seen. It gets on plane and breaks 60 unbeleavable in seconds.

Im gonna go to autozone and buy one of thoes cold air intakes to put on my procharger so ill get that extra 200hp like the ricers do. :lolhit:

Josh, my old 280 is now running a 675 hp 555 cu.in, and he can tap 80-81, but always 78-79, any conditions. I know this first hand because we boat together.
He runs either a tweaked 28 or 30 Bravo 1.
I'll check drive height with his. His drive height is stock as well as no spacers.
Have you checked for hull hook, just throwing this out there...
I always thought that a pro charger would give 100hp...but what do I know....

I base that comment on my personal setup. '97 MPI, 731 Crane cam (huge improvement over stock,) Dart 308s (mild improvement over stock,) Stainless manifolds (not holding any power back at this level,) stock everything else with an M1, and I'm not making 675hp. If I were, my little Fontaine would be running 90+. 5lbs is good for 100hp. 7lbs, maybe another 25? I stick by my comment...unless you have dyno numbers, you don't know how much hp you have. Period.

For drag cars.... Just like you're trying to prove on your boat, setup is everything....not power alone. HP has little to do with blowing tires vs chassis setup.

Not bashing you at all and am actually quite interested in your problem. I've recently made significant X and prop changes to my boat and am following the general practice of moving the drive up, not down. I also don't believe in the premise that just because someone else made a boat run XXmph with some hp and a prop that it should be able to be done to a sister ship, "because Bob did it." Every situation is different, no matter what. I wonder..... have you looked over your running surface with a straight edge for a hook or checked for any other anomalies that may be allowing more air?

For a rhetorical question, at what point does one realize that no matter how much money is thrown at a project, some things are just not meant to do what one is trying to get it to do? Sometimes you have to throw the towel and move on to a proven setup.

What's your next move, space it down?

Josh, have you run the boat without the 1" drive spacer?
whats the history of the spacer, why was it put on??

I think your last comment of it having a great hole shot says two things. 1 power is crazy because you would have snapped your drive by now. 2 a boat really set up for big top end takes a little to get on plane with out using tabs. Thy typically cavitate and slip with because of high x dim and can be a bit of challenge getting on plane.
You need to baby the boat up on plane or you will be replacing drives. Thu just don't like being hammered like that. No drive does.
You also need to pull the spacer and raise you x up and see if that helps. Should reduce torgue roll and gain top end. You will of course have to re prop to a bigger pitch to hook up and being the rpm's down. If it doesn't then go down even more. Will get slip numbers down but you may lose some speed. Also slip numbers can be fudged. People tend to over trim and get bad numbers. They test where how should and slip numbers are better but speed is lost so they dont like that answer and go back to over trimming when the answer is to get te x up.
I run a 30 stepped v single and have been through all this. It's a pain but it's trial and error.
It's frustrating to say the least because sometimes the experts answers are not correct for your set up and you feel like they give up on you.
You will get there... Eventually lol.

I was just trying to help. Being too rich will knock the hp down. I didn't realize that Mark tuned the engine in the boat with his laptop and a air/fuel meter.

Many times people think they have more hp than they actually do. So they put a bigger prop on and over trim it to get the rpms they want. What happens when you over trim your drive? Prop slip goes up. If it were me I would put on a smaller Bravo prop and see what kind of speed and rpms you get. Quick and easy and points you in the right direction.

And I never said the CMIs were costing you hp, I was merely stating that you get less gains on a SC engine. On a NA engine with bigger cams they make more of a difference because they scavenge better than stock exhaust.

Comparing a boat prop to a drag car's tires is like comparing an apple to a dog turd. But it sounds like you have it all figured out.