Cobalt merc. 250.

[avdoc]

I was given, (by my father-in-law), a very nice 1977 Cobalt. It is the 5.7L 250hp 350 ci. He was a physician, and bought it new. I love the boat because it is somewhat of a classic with the teak wood trim, and is heavy, so it rides like a 24ft. + boat on the local lakes even though it is a 19ft. I was told Edelbrock or someone had a intake/carb. kit for these, and it coupled with some aftermarket alum. exhaust manifolds really woke these engines up. Does anyone know of a carb. and intake combo. to use on one of these? If it were a car, I would.

 

[Don S]

Re: Cobalt merc. 250.

Is that engine a Merc, OMC, Volvo, or something else?

 

[avdoc]

Re: Cobalt merc. 250.

Sorry, it's a merc.

 

[achris]

Re: Cobalt merc. 250.

Hi there,

Merc have been playing with the SBC engines for a long time, since 1977. They have worked out, pretty well, what combination of cam, manifold and carb works best for a boat. Remember you don't have changeable gears so the engine's torque curve must be as flat as practical.

You could go changing a bunch of things and end up with an engine that will make 450hp, no problem. But it will have a very peaky torque curve and be virtually useless as a boat engine.

Chris........

 

[Bondo]

Re: Cobalt merc. 250.

It is the 5.7L 250hp 350 ci.

Ayuh,....... It already Has a 4bbl. Carb,........ Doesn't it,..??..??....

 

[avdoc]

Re: Cobalt merc. 250.

Ayuh,....... It already Has a 4bbl. Carb,........ Doesn't it,..??..??....

Yes it does, and he bought a "power pack" for it. I assume that was something with the ignition.

 

[FreeBeeTony]

Re: Cobalt merc. 250.

If it already has a 4bbl and it is running well.............I would leave it alone........

 

[avdoc]

Re: Cobalt merc. 250.

Thanks. I think I will pull the motor and take it to my engine builder and just have him go through it, freshen it up, replace bearings and rings, do a valve job and maybe some port work. I will probably just run it that way then.

Thanks guys for your help.

 

[FreeBeeTony]

Re: Cobalt merc. 250.

That sounds safe...............

 

[avdoc]

Re: Cobalt merc. 250.

That sounds safe...............

Serious, or you thinking something?

 

[FreeBeeTony]

Re: Cobalt merc. 250.

I'm being serious..........my vote is if it's not broke............don't fix it.

Is it running ok? Or is there something wrong warranting this work?

If you feel the engine is tired and you want to "freshen it up", maybe you should do a compression test to validate your suspiscions........

Just my opinion...........

 

[achris]

Re: Cobalt merc. 250.

Yes it does, and he bought a "power pack" for it. I assume that was something with the ignition.

Power pack is the ignition module. No pack, no power ....

Chris..............

 

[avdoc]

Re: Cobalt merc. 250.

Power pack is the ignition module. No pack, no power ....

Chris..............

True- but as an upgrade, it did not come with that particular ignition module factory. Some might, but according to him, it was an upgrade he added. I dont know. I spent several thousand upgrading ignition in my truck and hotrod, so I assume this is the boating version.

It seems to run ok, but the exhaust/cooling system seems to be somewhat sludgy, so I just figured since it is easy to pull the whole motor, I would have my race car engine builder go through it so I dont have to worry about it this summer. I have a 2 y/o who wants to learn how to ski, and I dont want to worry about it. I will use this boat to see if he really likes it, then I will get a malibu or something.

Thanks for all your help. I am somewhat new to dealing with boat mechanics.

 

[whywhyzed]

Re: Cobalt merc. 250.

....

 

[MikDee]

Re: Cobalt merc. 250.

I believe the 1977 250HP Mercruiser was actually a 327 (5.4L?), not a 350 (5.7L).
EDIT - maybe it was the 1976 255HP... there was oddly a 327 in around there somewhere many years after GM put them in cars.

This is true the 327 was used for marine, but by 77' I think they were 350 Chevys, around that time Merc. also used a 351 Ford Windsor style/ (255hp I think).

 

[avdoc]

Re: Cobalt merc. 250.

Interesting, I have not ran the casting numbers yet. The mercrusier tag says it is a 250hp 350. That may not mean anything. I supposedly had a 427 in my chevelle, and it was a LS7 454.

 

[achris]

Re: Cobalt merc. 250.

There should be a serial number tag on the block casting, above the starter motor. Although at this age it could well have corroded away. If you find the serial number we can identify it for you....

 

[avdoc]

Re: Cobalt merc. 250.

There should be a serial number tag on the block casting, above the starter motor. Although at this age it could well have corroded away. If you find the serial number we can identify it for you....

I will look today, as it is up at my shop for the winter so I can play with it. I doubt anything is corroded on this boat, it had hardly been used, and always covered out of the water on lift. I will post it later today.
Thanks

 

[Don S]

Re: Cobalt merc. 250.

Mercruiser used the 250 designation on 2 different engines.
First was the 327, but in 68 and 69 only.
They were also started using the 350 engine in 69, but it was called a 270
In 1977, there was a 350 called a 250. After 77, it was a 260 model.

 

[magster65]

Re: Cobalt merc. 250.

My neighbor took his '92 5.7 volvo (chev) apart. Being a 'car guy' he tore it down, put a more aggresive cam, some head work, intake and carb, electronic ignition... etc.
The sea trial with the gps before and after showed an increase of about 3 mph and it used more fuel of course. Worth it? I don't think so.