Inboard engine builds

About inboard or outboard motors.

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Re: Inboard engine builds

Postby Hercdrvr » Sat Dec 02, 2017 8:07 pm

I just dropped a 383 stroker with FITECH fuel injection in an old square body Suburban.....hello torque.
Too bad the marine version is 3X the money.
Matt B

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Re: Inboard engine builds

Postby DSR » Sat Dec 02, 2017 10:02 pm

Hi Denon,

I think you're heading in the right direction for what you want to do.
If this was my build, I would do the 496. Starting from scratch, it doesn't cost anything more for the extra cubes, and that American Turbine AA will like the torque.

I spent a little time cooking up what I think would be a nice, cost-effective recipe and this is what I would do......
Do the short block with a 4.310" bore (.060" over), 4.250" stroke for the 496 (internally balanced). 6.385" con rod length, 4032 forged flat tops (which typically use a 3cc valve relief cut in the face) with a 1.270" compression distance. Zero-deck the block (should be 9.780") and cut the tops of the cylinder walls to deshroud the intake valves.

The cylinder heads I would go with would be the GMPP 19331425 aluminums. Built by Edelbrock for GM from their Performer 454-O casting with a 110cc chamber but with a larger 2.250" intake valve instead of the standard 2.190" valve on the Performers (why Edelbrock didn't do that across the board on these heads I'll never figure out....) and at less than $2100 for the pair complete, some of the cheapest quality heads available.
Flat-mill the heads for 100cc chambers and you'll end up with a 10:1 static compression ratio, which will run fine with 87 octane because of the flat tops and the chamber design of the heads (along with the heat dissipation of the aluminum) and raw-water cooling in the boat.

I would use the Victor Jr. Oval port. The RPM dual-plane will put the torque curve in a lower rpm range than what you want for this application and won't have quite enough flow to properly feed a 496 at higher rpms. Professional Products Hurricane oval-port single-plane is also a good intake to use, and usually quite a bit cheaper..... With either intake, I would port-match to the intake ports with a slight mismatch on the outer port wall and floor of the manifold ports (just a touch smaller than the walls and floors on the heads to create a small step) to keep the air/fuel mixture in suspension, but not necessary, Just something I do on my builds for that "last little bit". Just make sure that there's no step in the ports from the head ports from the intake side to impede intake flow (I've seen this happen so I check every one of my builds for port alignment, even if I don't do any porting).

I would also regard an 850 carb to be bare minimum for this engine. Something in the 950 range would be better. Either vacuum or mechanical secondaries would be fine (and you will be spending time fine-tuning it, which is normal).

For the cam, I would definitely save the money and go with a nitrided hydraulic flat tappet as we've discussed before. It's just simply the best bang for the buck in this situation. Contact Terry Walters Performance Engines in Roanoke, VA, ... ommon/home

and do Vizard's COSCAM program to get the right cam for the job. Call him and tell him that it's for a marine application with wet headers and he should be able to set you up.

As far as the Lightning headers, I did some looking at those and they are a quality product. The only issue I would have with them would be the primary pipes being too short. I would personally try these first if it was my build (but they are a water-injected header as opposed to water-jacketed)..... ... aders.aspx

These have a much better primary pipe length (and I personally think they look pretty cool in a jet boat too.... 8) )

And above all else, visually inspect and measure EVERYTHING as you go through the build. Even the best companies with the best products and the best quality controls can have a bad day....

This should get you 600+ hp and 600+ ft/lbs in the RPM range you want in a strong, long-lasting combo for that badass boat you're building!! :D

If you have any questions Denon, just give me a yell!
DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."

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Re: Inboard engine builds

Postby wingridr » Fri Dec 15, 2017 10:47 am

I will try to incorporate my engine build into this thread. It is a Mopar 400 block with a stroker kit to bring it out to 470 ci. In street form, this engine built by someone else, has made up to 775 hp, and over 600 ft pounds of torque. This is spinning it to 7500 rpm, and the high torque hits about 4400 rpm. I plan to tame it down a bit to live in a boat.

I do have a couple questions that hopefully can get an answer. I see parts such as distributors and carbs being marine compliant. As we all know, the 400 was never a marine engine, although the 440 does share some parts with it.

I am planning on running a fuel injection system, and have located a “kit” that makes the engine distributor-less. By using these parts, would I be violating the federal stance on marine equipment? I assume these parts would be less likely to have an errant spark?

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Re: Inboard engine builds

Postby jenko » Fri Dec 15, 2017 12:48 pm

by fuel injecting the engine you get rid of the fuel vaporization problems and with coil over plug you get rid of spark issues, you still need a marine alternator and starter ,I also fitted a charcoal canister to my fuel tank vent which combined with EFI has eliminated any fuel smell even on the hottest days

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Re: Inboard engine builds

Postby wingridr » Fri Dec 15, 2017 4:54 pm

Good to know that my thoughts were correct! I guess I am lucky in that the marine 440 most likely uses the same starter. One of these days I’ll find one to pull parts from.

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