What is a Marine 350 Motor??

[BrassMonkey]

Ok here is my Question …

I am in the process of buying a older Boat that has a Goodwrench v8 350. The Motor was checked out by a Mechanic and has 2 cylinders with lower compression. My thought was to buy it and put in a new motor but what makes a Marine Motor a Marine Motor ?? My reason for questioning this is because I have a New Motor in the Garage for a Project Blazer, Can I swap it with my Crate Motor ???

[Boat Doc']

valve diameter, camshaft, pistons, in some cases crank type, head gasket material. You can use your blazer motor but it may not develop the same power as the original motor because of the above items possibly being different. Truck engines more closely resemble marine engines because of the lack of emissions.

[BrassMonkey]

OK Thanks .. If the Motor was a somewhat Built 400 I should be OK ?

Going to be Putting it in a 22 Foot Sea Sport

[EULACHON]

Gotta watch the somewhat built thing as marine engines develop hp at a certain rpm range.

The engine you have will work but may not get you out of the hole as quick or may produce the rpm's at a different time then the engine in the boat now.

Remember the marine components like starter and alternator will be different also. (sealed for spark)

Paul

[Orca]

And, brass freeze plugs.

[BrassMonkey]

Thanks good Points !


The 400 I have was set up for Hole shot hp .

[Boat Doc']

The only concern would be that the older outdrives could only handle about 260 hp. If used for fast starts or wave jumping the outdrive may not stay together.

[Fish mojo]

different starter- again, sealed for moisture.
I believe your camshaft would not be the same. Think of your truck engine as it accellerates, rpms climb- tranny shifts and the rpm's drop down. Finally you are cruising down the highway for extended times around 1800 rpm. Think of your boat getting up on plane, finally cruising at 3500 to 4000+ rpm for extended periods while cruising to your fishing spots. Totally different HP and torque requirements.

[BrassMonkey]

Let me ask you all this then ...The motor in the Boat now runs good doesnt smoke etc.. etc... I had the owner take it to a Marine shop to have the motor inspected and they found 2 cylinders with lower comp.What is good Comp in a Comp. Test ????

[broncos0707]

Comp test are fun. On a v8 you will want no lower then 115 psi per cylinder. and you want no more then 5 pound varience betweem any of the cylinders. I think the biggest dif. between a marine and regular enigne is the steel crank. You will need one. You will scatter a reg. motor if you run it at high revs with little to no load. :twocents:

[BrassMonkey]

How will I know if it is a Marine Moror? It has a Goodwrench motor in it now. Its not the original motor so how does one find out by looking at the motor? I am going to buy it this week. My fear is that they just bought a cheap long block from a GM Shop!

Please Help, many many Thanks!!!

[snit]

Far from an expert here, but maybe the "Marine shop" that checked compression can tell you? Might cost a little for "their opinion" but I think it would be money well spent?

Have ya had the boat "surveyed"? I think a surveyor is pretty cheap in the long run (maybe $500.00, again no expert)and that person would also tell you about the engine, as well as any possible "hidden suprises". I've NEVER heard anyone complain of having a boat surveyed, especially older glass boats.

[Quiet Riot]

It all depends on what you want out of it. There is a whitwater racing class that runs the gm crate zz350 rated at 345hp and no modifications are allowed. They fair pretty good for the punishment they are put through.

Generally, slight cam changes, brass casting plugs (freeze plugs) and marine starter, carb, dist, and alternator are used. Unless you get into aftermarket or high output engines, the oem marine manufacturers don't even do most mods most people think are in marine motors such as steel cranks, looser clearances, forged pistons, etc. And that is because they generally aren't needed for the low hp runabout type boat.

I ran a 400hp small block in a jet with a 250hp shot of N20 for 8 years without a problem, ever. When I tore down the motor there was hardly any wear with 400 hours of use. This was with a cast crank and tolerances set up for a street car as I originally built the motor for my mustang. But with an I/O you need to worry about idle charactaristics and torque curves and what your lower unit will handle powerwise.

Make sure the compression test was done with a warm motor and the throttle open otherwise the results are invalid. A leakdown test is a much more accurate way to diagnose engine problems if you want to know whats truly going on inside.

.02,
jd

[Orca]

Thanks QR. I had been through this before and had folks tell me marine motors have forged cranks, 4-bolt mains, forged pistons, etc. Not true. Your list covers it well.