OMC 5.0L vs. Chevy small block

[bradleyjc]

I have a quick question that may turn into a heated debate or may just be an easy answer, I don't know. My 88 OMC 5.0l needs replacing. I have a 88 Chevy 350 long block available to me. Question is, are they interchangeble or do I have to buy an actual marine long block? I've heard things like the rotation may be different or some of the accesories may not mount up correctly, and other things like this. I just don't know for sure.

 

[Bridar]

Re: OMC 5.0L vs. Chevy small block

Assuming your 350 is an automotive longblock, the main difference will be the camshaft, as a marine engine uses a slightly different hp curve. The accessories from the 305 should fit the 350. If your 305 is a 4 bbl, then the intake manifold & carb are the same ones used on the 350 (unless it's on a King Cobra).

 

[bradleyjc]

Re: OMC 5.0L vs. Chevy small block

Will the camshaft difference cause me any major problems?

 

[duped]

Re: OMC 5.0L vs. Chevy small block

First off, do you have a 5.0 chevy ( 305 ), or 5.0 ford ( 302 )???

Big differences there, and omc used both through those years if I recall.

Definitely not just a cam difference though. You well need brass core plugs, marine head gaskets, marine circulating pump, starter, etc. You will want to use all you can from the existing engine, or you will have issues. Automotive engines, and marine engines are certainly not direct swaps, but to answer the question, the accessories will mount up.

 

[bradleyjc]

Re: OMC 5.0L vs. Chevy small block

I have the chevy 305 OMC. The new automotive chevy 350 is just a longblock. I plan on swapping over all of the accessories from my marine engine, provided they fit. I'm just wondering if this will be a suitable replacment. Is this something people do, or is it just a bad idea all together? I have no problem changing the head gaskets out if need be, but I am not sure about the camshaft thing. Will my boat run right with an automotive camshaft?

 

[duped]

Re: OMC 5.0L vs. Chevy small block

You most likely will be okay with the cam in the replacement motor, especially if it came out of a truck. They use a similar grind to marine engines, and are designed for torque, which is arguably most important in boats. BUT if I was doing the swap, I'd get an RV/marine grind in there anyways.

You NEED NEED NEED to change head gaskets, and core plugs though. Corrosion will destroy them.

 

[bradleyjc]

Re: OMC 5.0L vs. Chevy small block

Awesome. Thanks for the advice. It is a truck engine so I will consider just using that cam unless I can find a marine one for cheap. But I will change the head gaskets for sure.

 

[Fishermark]

Re: OMC 5.0L vs. Chevy small block

If this is a new longblock from Chevy, then the chances are good it already has a composite head gasket and brass core plugs. If it is a used / rebuild long block, then it may not. You can always scratch the paint off the core plugs to see if they are brass or steel.