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Old 05-05-2021, 10:55 PM   #1
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Default Mercruiser 5.7l replacement alternatives

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...?


Best wishes,
L


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Old 05-06-2021, 01:24 AM   #2
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You forgot the casting (freeze) plugs are different as well as the carburetor. A marine rebuilt long block isnít 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 youíll need to source a new cam. IMO itís not worth the extra work to properly convert an automotive engine over just buy the correct one.
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Old 05-06-2021, 01:41 AM   #3
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You forgot the casting (freeze) plugs are different as well as the carburetor. A marine rebuilt long block isnít 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 youíll need to source a new cam. IMO itís 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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Old 05-06-2021, 11:00 AM   #4
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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.
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Old 05-06-2021, 12:06 PM   #5
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Originally Posted by LexiP View Post
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.
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Old 05-09-2021, 04:36 PM   #6
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Donít forget to compare the internals as well.
Steel vs cast crank, rods, etc.
marine engines are under continuous load vs automotive that arenít.
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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Old 05-09-2021, 06:05 PM   #7
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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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Itís not just the rpm itís 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 itís like going up a steep incline all the time.
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Old 05-10-2021, 03:12 AM   #8
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Itís not just the rpm itís 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 itís 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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Old 05-10-2021, 04:14 AM   #9
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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 itís 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.
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Old 05-10-2021, 11:25 AM   #10
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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 youíll get a different response.
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