Mercruiser 5.7l replacement alternatives

[LexiP]

Hi All,

I do not need to replace the engine now. But I'm curious.

From what I understand my MerCruiser 5.7l is marinazed version of Chevy small block 350 engine. And the marinization is:
1. Different camshaft;
2. Different exhaust manifolds (duh!);
3. Different dipstick and dipstick tube;
4. 160F thermostat;
5. Marine grade alternator;
6. And maybe marine grade starter.

Does it mean that I can pull my engine out, walk into Advanced Auto Parts, grab new Chevy 350 engine for $1,400, replace the cam, move all the covers and accessories from my old engine and slap the new engine back in...? [emoji2955][emoji2955][emoji2955]


Best wishes,
L


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[mmwjr]

You forgot the casting (freeze) plugs are different as well as the carburetor. A marine rebuilt long block isn’t much more than an automotive one and is built to tighter specs. Automotive rebuilds can be bored .060 over which is twice what a marine rebuild would be and this thins the cylinder walls closer to the cooling jackets which if raw water cooled is less thickness for corrosion to eat through. Plus you’ll need to source a new cam. IMO it’s not worth the extra work to properly convert an automotive engine over just buy the correct one.

[LexiP]

Originally Posted by mmwjr

You forgot the casting (freeze) plugs are different as well as the carburetor. A marine rebuilt long block isn’t much more than an automotive one and is built to tighter specs. Automotive rebuilds can be bored .060 over which is twice what a marine rebuild would be and this thins the cylinder walls closer to the cooling jackets which if raw water cooled is less thickness for corrosion to eat through. Plus you’ll need to source a new cam. IMO it’s not worth the extra work to properly convert an automotive engine over just buy the correct one.

Freeze plugs don't seem to be a problem, especially keeping in mind that I plan to use automotive antifreeze.
Carburetor would come off the old engine.
I didn't catch the boring part - Advanced Auto Parts sells an assembled engine core with block, crankshaft, piston rods, pistons, heads with valves, rockers, etc, and camshaft. It comes without accessories, carb, manifolds, and covers.
New cam available online as a kit for $220.

Cheapest marinazed Chevy 350 is over $3,000 that is without manifolds, covers, and accessories. Drop in engine is about $9K for a carburetor version, and almost $12K for MPI version.

I see quite a difference between $1,400 + $220 and almost $9,000. That is with comparable amount of work. Would you agree...?

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[jparsons121]

Don’t forget to compare the internals as well.
Steel vs cast crank, rods, etc.
marine engines are under continuous load vs automotive that aren’t.

[mmwjr]

Originally Posted by LexiP

Freeze plugs don't seem to be a problem, especially keeping in mind that I plan to use automotive antifreeze.
Carburetor would come off the old engine.
I didn't catch the boring part - Advanced Auto Parts sells an assembled engine core with block, crankshaft, piston rods, pistons, heads with valves, rockers, etc, and camshaft. It comes without accessories, carb, manifolds, and covers.
New cam available online as a kit for $220.

Cheapest marinazed Chevy 350 is over $3,000 that is without manifolds, covers, and accessories. Drop in engine is about $9K for a carburetor version, and almost $12K for MPI version.

I see quite a difference between $1,400 + $220 and almost $9,000. That is with comparable amount of work. Would you agree...?

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Automotive long block for a 5.7 is $1800 from Auto Zone, most marine long blocks go for around $2400 from online suppliers. Neither of these include the tin work their just the block, heads and all internals.

[LexiP]

Originally Posted by jparsons121

Don’t forget to compare the internals as well.
Steel vs cast crank, rods, etc.
marine engines are under continuous load vs automotive that aren’t.

I actually would think that utilization mode for automotive engines is by far harsher then of the marine engines. Engines don't like constantly shifting rpms, but don't have problems working on the same rpm for hours. Otherwise "highway miles" wouldn't exist.

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[mmwjr]

Originally Posted by LexiP

I actually would think that utilization mode for automotive engines is by far harsher then of the marine engines. Engines don't like constantly shifting rpms, but don't have problems working on the same rpm for hours. Otherwise "highway miles" wouldn't exist.

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It’s not just the rpm it’s the load on the engine. A marine application is a.ways under heavy load while a car has a transmission and free wheels part of the time. For a boat it’s like going up a steep incline all the time.

[LexiP]

Originally Posted by mmwjr

It’s not just the rpm it’s the load on the engine. A marine application is a.ways under heavy load while a car has a transmission and free wheels part of the time. For a boat it’s like going up a steep incline all the time.

I'm still not convinced. Even under constant load (like in a generator) but with (more or less) constant RPM I don't see it as a heavier utilization comparing to constantly changing rpms.

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[jparsons121]

Originally Posted by LexiP

I'm still not convinced. Even under constant load (like in a generator) but with (more or less) constant RPM I don't see it as a heavier utilization comparing to constantly changing rpms.

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In the end it’s your decision....
I can understand the urge to justify using the automotive engine due to the price difference. Like others who have commented, there are differences and from experience building both marine and Circle track race engines, the application dictates what is best.

[mmwjr]

Originally Posted by LexiP

I'm still not convinced. Even under constant load (like in a generator) but with (more or less) constant RPM I don't see it as a heavier utilization comparing to constantly changing rpms.

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Your boat, your money do as you please. You asked the question and we replied. Go to any other boating forum and I doubt you’ll get a different response.