The Stovebolt Site Forums The Shop Area Engine Shop 5.7 Marine engine conversion

Have access to a 5.7 Chevy V8 set up for marine operations. I’m not familiar enough with these to know exactly what changes need to be made for use in a 1984 Chevy 1/2 ton. Engine still has all the marine stuff on it but has been removed from the boat and of course separated from the outdrive. Exactly what needs to be removed/changed/purchased to be of use to me? Thanks

Exhaust manifolds, for sure. Marine engines use exhausts with built in water jackets. On twin engine boats, one engine usually runs backwards, like the Allison V12s on a P-38 fighter plane. The torque reaction on the props cancel each other out to prevent the boat from trying to run in circles. Reverse rotation engines have an oddball gear drive for the camshaft, and a rear oil seal that must be swapped out. Most marine engines will have a lot more "full throttle" hours than street engines, so they're usually built with racing engine bearing and piston clearances- - - -a little looser than a land-based engine.
Jerry

A friend has a boat with two outboards. We were on a trip in it when the reverse rotation lower unit crapped out. He was unable to get a replacement reverse rotation lower unit, so put a standard rotation unit on it. Next time he took it out, he found he had gained 5 MPH in top speed, about a 10% increase. All the boat people said "That can't happen" but it did. He has no issues with the boat trying to run in circles.

It depends on the size of the props, and how much torque they can exert on the stern- - - -the bigger the prop, the more side thrust there will be. Container ships with huge single screws have to run computerized steering correction to run in a straight line.
Jerry

I would also guess that the water pump and maybe the intake manifold would be different than a truck engine, I can't remember if they ran a Q-jet on the marine engine, I don't think they did. The throttle linkage is totally different from truck to marine but that should be simple if you go with a Q-Jet. Probably need some front accessory drive pulleys and brackets, there will be no fan on the marine. All of those parts are a dime-a-dozen. You could probably find another 350 at a yard and use all of the exterior parts as needed. If you look for one from roughly the same vintage as your truck, the brackets should put you in business.

HRL, this is from a single single engine boat, so no counter rotation issues. Thanks

78buckshot, engine is carbed but I haven’t seen it so not sure what carburetor it has. Water pump, brackets and pulleys it is. Thanks

Martin -- was that engine run in fresh water or salt water? Considering your location, I'll guess fresh. If salt water ....

John, it is indeed a fresh water engine. Don’t know the hours as the boat was cut up and scrapped a couple of years ago. It will cost nothing to get it but I’m thinking it will need a bit of refreshing. Trying to work up a budget to get it at least running.
Thanks all!

Martin, one thing I'vwe observed on the fresh water run marine engines I've rebuilt- - - -I don't think I've ever seen one with enough cylinder wear to need to be rebored. A good friend who has spent most of his mechanical career around houseboats and other large water craft like cabin cruisers has expressed the same opinion, and he claims that's because a propeller doesn't put as much torque load on the crankshaft as a mechanical drivetrain does. On the other hand, a boat is running "uphill" all the time- - - -trying to climb out of the hole it's in!
Jerry

Remember the marine engines use a electronic thermostat on the cooling since there is no recirculation since its pulling water from outside and no radiator closed loop system.
its a easy swap to automotive type as you are replumbing all the hoses anyway.

On the big rigs they run heat exchangers. The main cooling system runs a thermostat and regular antifreeze, which is circulated through a water-to-water heat exchanger that circulates outside water around a copper core containing the coolant. That also prevents salt water from getting to the engine(s) on offshore rigs. The heat exchanger has its own water pump for circulation.
Jerry

Another difference is that most marine engines, at least the ones I've run, operate at a constant rpm most of the time. Unlike land engines that are over the rpm band.

If the op has the time and money, checking the compression ratio and choosing a camshaft for his intended purpose may be in order, I'm just guessing that a marine cam may be different than a truck cam due to the more constant RPM of the marine engine.

Most of the marine engines I've worked with have a cam similar to what would be used in a medium-duty truck- - - -with more emphasis on torque and smooth idle than maximum horsepower. That seems to be pretty useful for a pickup as well. Fairly short duration, with a quick lift rate to get the valves open quickly and hold them open for as long as possible to allow the engine to breathe well at low to midrange RPM, without the choppy idle associated with high HP- - - -high speed cams. That's also where a "street roller" cam shines- - - -slap the valve fully open quicker than a flat tappet cam can, and hold it there as long as possible before closing quickly.
Jerry

He should be good to go then if it has been maintained.

We picked up the engine last night and had a very pleasant surprise. The engine had been abandoned by the previous owner in a garage belonging to my son’s wife’s aunt. He had only seen the engine in the dark by flashlight. Turns out this engine is a brand new 5.7 crate motor fully rigged for marine use. Zero hours, new oil, paint not even worn off the belt pulleys. Scoped the cylinders and absolutely no wear, no deposits on the valves and new plugs. Numbers were run by both the local PD and the County Sheriff and came back clean. The property owner paid us to remove it as part of the property cleanup. 14 year old grandson now has a “new” engine for his 1984 Silverado that he and Dad (Terry B) are building. Happy campers all around.

Wow, What a score! Congrats to your son and grandson!

Martin, that is an amazing find! Now the bar has been raised...gotta build the rest of the truck to the new engine standard. Said the man who has absolutely no skin is this game. Best of luck to all.

RonR

Recently watched a YouTube video where some builders were prepping and installing a marine 454 into a vintage car. The engine was far from new, but the cleanliness and condition of the internals would make one think it was brand new.

Their theory was that marine engines eat zero dirt, at least by comparison to road vehicle engines. Jerry’s comments about the different torque load also makes some sense.

What a luck find. Must be all that clean livin'.