Velocity941

You're a drag racer! Spray it with a 150 jetted fat and see how the boat responds. Should be simple...then you'll know what hp to target in your build...

techman

Also remember in your search for more HP and more speed your DP drive will quickly become the weak link. You will have to upgrade your drive and that will require some transom work. I'm pretty sure the Volvo cutout is unique.

Adding to your budget! Controls....gauges...glass work....

Brad Christy

Drag,

That was my intentions, too....

That link was meant as a deterrent, in respect to building a 632ci. I am, by no means, an engine guru, as I have never built even that first one. But there are many on here that have. Marine in particular. Within the comments of that thread, you'll read advice to not exceed 4.25" stroke, due to rod angle and duty cycle of a marine engine.

By all means, build that engine, but consensus says to stop at 565ci, or 4.25" stoke and 4.600" bore. That's all Mercuriser's 1650 is. Well.... That and a couple of massive turbochargers.... 🙄😎

You'll also discover, upon reading other threads on the matter, that it is the valve train that must be paid particular attention to. Marine engines are often put on the firewall for extended durations, and it seems it's often the valve train that is the impetus for a catastrophic failure, assuming proper AFRs are maintained.

There is a wealth of knowledge here on OSO on building high output marine engines. Exploit that, regardless of your knowledge base.

Thanks. Brad.
(937)545-8991

Brad Christy

Dragracer,

There are a couple of 496's (maybe even HOs) available here on OSO, as are a couple of BravoXR drives. See what you can get for your money there, assuming you can sell a complete Volvo 8.1/drive package to recoup some of your costs. At least there won't be any trying to make THIS work with THAT if it's all Merc stuff.

I know of a couple of Rinker 262ss' on Cumberland that have this exact package that are in the 65-70MPH range. I doubt your Chappy is all that much different.

Something to think about.

Thanks. Brad.
(937)545-8991

Dragracer_Art

I like the idea but the top ring land is too high in these 496's. Im sure if I put some juice to it the top ring land will break off.

Brad Christy

Dragracer,

Specific to Merc.... (Don't know crap about Volvo)

If you can find a 496HO that has the forged rotating assembly (the transition occurred around '01-'02, and they can run the serial numbers at Merc), and you stay away from any real boost, it's a relatively bulletproof engine.

I've got a 496HO with an M1 ProCharger (3lbs) that ProCharger advertises at 615HP (realistically putting it somewhere between 425 and 615HP, right?), and it's a pretty reliable package. Just for reference.....

Thanks. Brad.
(937)545-8991

Knot 4 Me

To my knowledge the only forged part ever in a 496 MAG HO was the crank very early on and that quickly was changed over to cast. 496's never had forged pistons.

For reference...

Knot 4 Me

Another obstacle in your way is the goofy side exit exhaust. If you figure out a better transition and remove any baffling your passengers are going to hate riding in the back.

techman

I always thought side exhaust was a weird design. Is it done for packaging reasons? It certainly can't be for sound since you are hearing 4 out of sync cylinders on each side. It makes that V8 rumble sound like a UPS truck.

boomer

Do a goggle search there was a guy that tried almost 600 hp in a 256 not worth it that boat is not meant to go fast, also you need those 6" risers ( that motor sits deep in the boat) so you dont get water back up the exhaust when you slow down. Trust me I know I own a 256 its a great family bow rider I have 8.1 and that's my speed 55-57 but it s a great family boat.