Boat currently has 454 mpi mag with Stainless Marine Exhaust. Turns a 24p 5000rpms at 69mph. Procharger claims 620hp at 5psi of boost. What kind of speed gains should I expect? Before everyone starts in on me, I'm adding dual ram hydraulic steering before the procharger. Boat is a 1999 pq Raizor 22

With that much hp increase, you will have to change your prop.

Of course, any idea how big of one I could turn? 30? If so that'd put me in the mid 80's

Your not going to spin a 30. Probably have no problem spinning a 26. Might struggle to spin a 28.

Even if it makes 550, you are picking up 200 HP.

Couple things:
Take a hard look at the fuel system from the tank to the injectors

Consider head gaskets and ARP bolts

Crazy not to spend some time on the heads while apart

Odds are you'll want to get the prop shaft higher to get the speed gain you expect.

If 600 HP won't turn a 28-30 P prop on a 1.5:1 ratio in a 22ft boat, the hull isn't worth the work!

According to the BAM speed calculator, with 620 HP, you will be in the 85 MPH range

http://www.vortechsuperchargers.com/
The only one to go with.
It's going to make your nice dog into a mad dog.
Or like putting your foot in a Hornets nest.

Vortech does it right the first time to last a long time.
And you can clean the chiller on a Vortech.
Can not do that with the Procharger chiller.

24ft checkmate went from 66mph to 84mph still playing with props - that was on a 454 MAG MPI. So depending on your hull I think a 10mph gain should be fair to expect which is A LOT

Lots of info here. http://checkmate-boats.com/forums/sh...ad.php?t=31932

Planned on doing some minor head work while replacing head gaskets and are bolts. I think the hull will be ok. It has a single step right on the keel 6ft from the transom. Also the strake on each side of the center stops at same spot. What does this small step actually do for it. If I sound ignorant about boat hulls....it's because i am, but I learn quickly