Engine rebuild questions 5.7l

First off I'm not sure if this is the right section of the forum to be posting this but i thought i would give it a shot. Its an OMC set up with a GM 350 5.7l. Its time for a rebuild on the motor. I was told to run marine gaskets in the engine and I was wondering how crucial this is as opposed to running normal automotive gaskets. Also, Will swapping in an aluminum intake and a better cam help out on the water? WOT is about 3k rpm or so, Id like to be able to give this thing a little more pep. I'm also toying around with the idea of swapping in a 350 diesel, anyone have any ideas on the matter?

which gaskets are you asking about?

brand new GM crate 350/290 probably less money than cost of rebuild and is basically the marine 260HP motor of the early 80's. Swap in brass core plugs.


don't understand the cam question. help out on the water? what water?

What's a 350 diesel? You mean the old GM car piece of junk thing from the 80's? They made about 115HP on a good day... I wonder if you'd even get on plane.

All the gaskets for a full engine rebuild, oil pan, timing cover, front and rear main seals, head gaskets, intake gaskets, valve cover gaskets.
I know a cam helps out cars on the street, just wondering if it would make much of a difference in a boat.
I guess that answers that about the diesels lol

all the gaskets are the same - marine engines do require special head gaskets if raw water cooled, but all modern, high quality rebuild kits come with nice composite gaskets with ss fire rings which are great for marine use (Fel-Pro etc)

In a car, a performance cam allows the engine to make more power at higher rpm's. A driver capitalizes on that by shifting at higher rpm's, or putting in a high stall torque converter

Boats don't shift, nor do outdrives allow the engine to turn higher rpm's so generally, no... the marine cam is already a high performance cam as far as lift and duration. similar to a truck or "RV" cam, but with some other special features to prevent water from the exhaust from entering the intake valves. Car camshafts often have valve overlap that would damage a marine engine from exhaust water.

Hi I have a 5.7 diesel that has just been re built.
it has a barr marine exaust kit on it & uses a bowman header tank. is there any point in fitting a air cooler to it ?

What omc drive is it going to be hooked up to ?

Is it going in a boat, this motor ?

Reason i asked, i have never, ever, heard of any diesel in front of any omc drive.

If you really want good sound advice this isn't the forum, you need one with diesel mechanics, and you might add some of the info i asked you for.

In all due respect to you sir; if i were you i would start a NEW thread in the correct diesel forum.

Good luck !

incredibad said:

First off I'm not sure if this is the right section of the forum to be posting this but i thought i would give it a shot. Its an OMC set up with a GM 350 5.7l. Its time for a rebuild on the motor. I was told to run marine gaskets in the engine and I was wondering how crucial this is as opposed to running normal automotive gaskets. Also, Will swapping in an aluminum intake and a better cam help out on the water? WOT is about 3k rpm or so, Id like to be able to give this thing a little more pep. I'm also toying around with the idea of swapping in a 350 diesel, anyone have any ideas on the matter?

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forget about diesel and the cam.


what you need to worry about is..... 3K RPM at WOT???


Should be 4600-4800 fix that and you will see a performance increase.

On my 5.7 OMC 3K RPM is just up on plane. About half throttle.

The only V8 GM diesels I can think of are the horrid 6.2 and the not much better 6.5. Using one of these monsters will be a bad move. While you may be able to get a drive coupler on there and even get it hoisted in the boat, it is about 300 pounds more than a regular 350 gas engine and only puts out about 150HP. It's also not going to spin more that 3200 rpm.

Remember your marine engine is always going "uphill", the faster you push it the more uphill it has to go. The things you do to a car engine to make it faster won't work on a boat engine. Best bet is the crate engine noted above along with a fresh new 4 barrel carb and center riser exhaust manifolds. The MSD wasted spark marine ignition is also a nice addition and will work with the OMC shift interrupter. Turbo supercharging with a air to water intercooler can tack on another 50% increase in HP.

This thread was started over 4 months ago..... wonder what he ending up doing! Hmmmmm.... dinner, movie, cocktails and dancing......., and yet no kiss at the front door??????

You've left us hanging here, Mr. Incrdibad!

incredibad said:

First off I'm not sure if this is the right section of the forum to be posting this but i thought i would give it a shot. Its an OMC set up with a GM 350 5.7l. Its time for a rebuild on the motor. I was told to run marine gaskets in the engine and I was wondering how crucial this is as opposed to running normal automotive gaskets. Also, Will swapping in an aluminum intake and a better cam help out on the water? WOT is about 3k rpm or so, Id like to be able to give this thing a little more pep. I'm also toying around with the idea of swapping in a 350 diesel, anyone have any ideas on the matter?

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I think swapping in a 350 diesel is a good idea. I tried it before and it was good. There is no problem about it just try it.

i agree he don't have to go faster then 10 mph anyway.

RicardoMarine said:

This thread was started over 4 months ago..... wonder what he ending up doing! Hmmmmm.... dinner, movie, cocktails and dancing......., and yet no kiss at the front door??????

You've left us hanging here, Mr. Incrdibad!

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4 months....? and I was getting interested to read all the posts from the start.

knickick said:

Re: used engines rebuild questions 5.7l

Originally Posted by incredibad
First off I'm not sure if this is the right section of the forum to be posting this but i thought i would give it a shot. Its an OMC set up with a GM 350 5.7l. Its time for a rebuild on the motor. I was told to run marine gaskets in the engine and I was wondering how crucial this is as opposed to running normal automotive gaskets. Also, Will swapping in an aluminum intake and a better cam help out on the water? WOT is about 3k rpm or so, Id like to be able to give this thing a little more pep. I'm also toying around with the idea of swapping in a 350 diesel, anyone have any ideas on the matter?



I think swapping in a 350 diesel is a good idea. I tried it before and it was good. There is no problem about it just try it. ​

Click to expand...

I got it figured out thanks