Anybody know marine vs automotive GM 4.3s?

Anybody know about the specifics of swapping a marine 4.3 into a 98 s10?  Same year engine and truck, have current knocking 4.3 in the s10 to scavenge parts from.

Trying to find actual answers on the s10 forums is like trying to pull teeth from toothless mouth breathers (unless you stumble on a duster post).  From what I can find (based on actual experience), marine short block is interchangeable and marine engines are 4 bolt mains.  Heads may be different, I can swap my heads over.  Intake, oil pan, oil pump/pickup, and timing cover may need swapped.  Cam may or may not be different, but I can swap.

I saw talk about intentionally plugged coolant passages in marine engines, though I can't remember if that was 4.3 specific. 

Engine was fresh water only, ran great, 400 hours.  I'm ok with a slight project given the $, but if it's going to be a pain I'd rather put the time and money into a v8 swap.  

Thanks in advance for any info.  I know I'm going to get "v8 swap it bro!", which I agree with, but my buddy Patrick, who would LS swap your mom, told me to slap a cheap 4.3 in it and get back out on the road bc the 4.3 does everything I need (light truck/rallyx).  He then told me the same thing again a few months later.  It's probably 6 months later and I still haven't done E36 M3 on the truck.  I have plenty of other projects to work on, and I really want to rallyx this year.

Generally speaking, marine engines have weird exhausts, are designed for a powerband that is maybe 500RPMs wide up near WOT, and the cooling systems are tweaked to run on a never-ending supply of constant temp water.

Long block, and possibly heads, should be the same.  Exhaust and intake will be different, cam may be optimized for single-RPM power and to prevent water from being sucked in via exhaust scavenging.  Freeze plugs and head gasket may be different as well to cope with different environments.

May have forged bits for the constant WOT abuse.

Although Mr Asa is correct in many applications, the 4.3's before the mid 90's were almost the same, marine wise. Even have a good cam for the street. Same long block otherwise. All the different parts were external. Now when GM added the ballance shaft in the mid 90's, and CPI intake after that, (both of them are on the 98 you have) I don't know when the marine engines followed suit; so be careful of that.

Look at a forum  https://www.astrosafari.com/index.php, and a guy by the name of  chevymaher used a marine long block in his 92 Astro. You get a bit less of the s10 croud maturity level attitude over there.

Once you pull off the marine exhaust manifolds, it's basically just a standard 4.3 (not necessarily 4 bolt) with a slightly different cam and a different oil pan.  Intake manifold and heads are probably nothing high performance, but may or may not be much different than what the truck started with (other than being a carb intake).  Most of the automative based marine engines aren't anything all that different or special. 

Some sources claim that the marine version runs greater piston clearances due to the high loads often encountered with boating. The clearances are said to be .008 to .010" in marine and less than .003 in automotive versions.

Lots of good info here, but a couple things to clear up.

The 4.3L in the boat is most likely the exact same casting that came in the car, right down to the heads, cam, block, crank, the works.  

Things that are different:

- intake manifold water crossover is likely cast with a bronze liner
- water pump will not be compatible with an automotive application.  Marine water pumps are in the outdrive.  The water pump on the marine engine is likely just a straight-vane circulator pump to grab what the outdrive gives it and send it through the motor.  It is a weak, supplemental pump, not adequate for being the only pump.  Also, some of the SBC and 4.3L marine applications use a corvette-length pump which is neither tall nor short.  For that reason you may need to use the accessory drive and water pump from the truck.
- alternator, distributor, and starter are all equipped with spark arrestors, and the distributor will not have a vacuum advance provision, just mechanical.
- carburetor may not have the throats drilled for a ported vacuum source.

Things that are not different:

- pretty much everything else except the exhaust manifolds (obviously).

The cam (depending on Volvo/Mercruiser/OMC) is likely either the stock 160-hp cam that they order along with the crate engine from GM, or they order it without a cam and use (you guessed it) a Melling re-grind of the same cam.  Mercruiser is about the only one that specs their own cam, but that's on the 5.0L and 5.7L, and the only real difference is that they spread the LSA out one more degree.

One word of caution.  If the marine engine was ever run in salt water, do not put glycol coolant in it.  Salt sticks around for a long time in the pores of the iron and if it's in a high enough concentration it will cause a heap of trouble since it doesn't play well with antifreeze.  If you're concerned about it, fill it with straight water and an additive (lubes things and prevents corrosion) and leave the thermostat out.  Run it as long as you can that way with a couple drain and refills... like a few months.  Then, before next winter (or if it looks like it will get below 30-ish), then add 50/50 mix.

FMB42 said:

Some sources claim that the marine version runs greater piston clearances due to the high loads often encountered with boating. The clearances are said to be .008 to .010" in marine and less than .003 in automotive versions.

This was true in the 60s, but not today.  In the old days, metallurgy sucked and the only way to get a piston to survive was to use a forging.  These days with hypereutectic technologies and better castings, the whole thing is an off-the-shelf GM crate engine.  In many cases, even the gaskets are automotive spec.

Personally, even if it only saw fresh water, in my mind, any marine engine that was run without a closed cooling system is junk from the first turn of the key.  I wouldn't buy a boat without closed cooling and I'd certainly never re-purpose the engine into anything else. 

"This was true in the 60s, but not today."

The GM 4.3 engine was introduced in the mid '80s. The marine version came out a year so later.

In reply to FMB42 :

I wasn't speaking about the 4.3 in specific, I was speaking of marine engines in general.

The bottom line is that since about 1979, marine engines have primarily been crate engines purchased from the manufacturer with little or no difference from their automotive counterparts.

Someone was telling me that Chevy marine engines were balanced to a much closer tolerance than automotive engines.

rslifkin said:

Personally, even if it only saw fresh water, in my mind, any marine engine that was run without a closed cooling system is junk from the first turn of the key.  I wouldn't buy a boat without closed cooling and I'd certainly never re-purpose the engine into anything else. 

Care to share why?

Curtis73 (Forum Supporter) said:

rslifkin said:

Personally, even if it only saw fresh water, in my mind, any marine engine that was run without a closed cooling system is junk from the first turn of the key.  I wouldn't buy a boat without closed cooling and I'd certainly never re-purpose the engine into anything else. 

Care to share why?

A few reasons.  In salt water, there's the salt buildup issue.  There's corrosion issues even in fresh water (just not as severe as salt).  Because of the lack of cooling system pressure, if they've ever gotten a little bit warm the thing has boiled water in the heads, leading to potential pitting and damage on top of warping and gasket concerns.  That same lack of cooling system pressure also forces them to be run far colder than optimal, leading to higher wear, more oil dilution, etc. so they age much faster than a closed cooling or non-marine application. 

Having seen the corrosion issues that happen in a car when someone runs straight water in a cooling system for a period of time (or very old, worn out coolant), I wouldn't want an engine that's intentionally had just straight water run through it. 

Raw water cooled marine engines also run the exhaust manifolds colder than a full fresh water system, so there's more condensation in the manifolds and such after shutdown that can corrode the exhaust valves (even without accounting for any failed exhaust components). 

In reply to rslifkin :

I can dig that.  Those all make sense, but in reality I've never experienced any of that in real life.  Most marine engines also get used three weekends out of the year and then get drained.  The 305 I pulled out of an old Baja was wasted from the inside because it was uncovered and water got in the intake, but the jackets looked pretty good.

Curtis73 (Forum Supporter) said:

In reply to rslifkin :

I can dig that.  Those all make sense, but in reality I've never experienced any of that in real life.  Most marine engines also get used three weekends out of the year and then get drained.  The 305 I pulled out of an old Baja was wasted from the inside because it was uncovered and water got in the intake, but the jackets looked pretty good.

 

True, most don't get used much.  On the other hand, we put just shy of 90 hours on the pair of (closed cooling) 454s we've got in the boat last year.  One was replaced a few years ago after an oil line failure took out the main bearings, but the other is at 1700 hours and still healthy, so something has been done right.