Looking at a set of Dana Marine manifolds right now... these are supposed to be good for 40+hp out of the box.
Apparently the VP manifolds and stupid-tall risers are horribly restrictive.

Currently in talks with Marine Industries West trying to figure out a riser/spacer combo that will work with my system. May need to shorten my Corsa drop tubes to the Y-pipe to lower the system a couple inches... or stack Dana spacers to raise the Dana system.

Just need to get busy with a tape measure.

https://www.marineindustrieswest.com...productid=3670

Mine is a Volvo Penta drive-by-wire system and apparently nobody tunes them. I've tried everywhere... Whipple, Hardin, MEFI Bob, etc...

Larry Hofer said the GXi ECM is a plug-n-play upgrade to my Gi ECM and will work with his 525hp heads/cam package. He also speaks highly of the Dana Marine manifolds noted in my previous reply.
A GXi-H ECM, part# 3889007 is what should work in my 2007 boat... but very difficult to source one.
The current engine/ECM:

Also worth a mention...

On the Facebook Chaparral owners page... there's a guy with another 256ssx for sale. Same boat as mine.

His is powered by the mercruiser 496HO that I had been shopping for... unfortunately his hit the market a few weeks too late and $10k too high... BUT... he is advertising that his boat will go a GPS verified 65mph with the current combo.

The previous owner of my boat claimed he has nipped 60mph with it already... but I cannot confirm if that was by GPS or a generous speedometer... so maybe my 55.4mph run was a little low/premature. New from the factory they claimed 56mph with this engine in it.

Either way... it's lends credibility to the possibility I may be able to push this hull to 65mph without spending $100k to do it.

Stay tuned.

A 256ssx with a 496HO has 50 more HP than your mill. I'm not convinced it is 10mph faster however.

When I did customer deliveries for a Cobalt dealer, the Merc boats were always 3-5 mph faster than the Volvo boats when comparing Gi/Gxi to the non HO and HO motors. We did have one customer that ordered a 496 HO boat with a Bravo 1 and that was clearly faster than the B3 boats by a good margin.

So... in a nutshell... there IS room for improvement.

I'll take that as a positive development.

Incremental improvement is going to frustrate the pee out of you.
Drop 2 grand - convince yourself you see 2 mph from it, but you know in your heart that it is more like 1.2 mph.
Drop another 2 grand - maybe-another mph.
Drop another 3 grand - picked up 2 more real mph but made it a hassle to get on plane..

You have said ONE thing in all of this that made good sense. Build an engine. A 600hp big block with carb. Drop it in. Go run it. If you don't like the results, Drop it in a Camaro.
If you do like the results, then determine how much of the VP fuel injection stuff you want to try to transplant over to it.

Yeah... I am leaning in this direction.

I will give a buddy of mine a call and see what he can whip together for me. Andy Jensen is pretty well known in Drag Racing and has always been my go-to guy for machine work.. been friends with him since mid-90's.

Last big boy I built was this 632 in my Camaro in 2004. It made 881hp at the rear wheels on a single Nickerson Dominator.

I'd love to have something like this in my boat... but obviously detuned for pump gas and hydraulic roller.

Nice looking split bumper

Dragracer,

Dart Big M Block Questions - Offshoreonly.com

Thanks. Brad.
(937)545-8991

One thing I was pleased to learn already is that the 8.1/496 motors are already a tall deck platform.
This should make the swap pretty straightforward with respect to exhaust port height/alignment and engine compartment fit.

I think a 10.2 block with a 4.600 bore and 4.5" stroke would be a pretty bulletproof and reliable combo @ 598 cubes and should be a pretty clean swap.

Thanks for the link above. I will read through it !