Engine upgrade?

[series60]

I am looking to the near future replacing my tired salt laden 1984 305SBC with a newer version 350SBC. What specific items must I be aware of when looking at a newer vintage 350, say something in the mid 90's. What parts interchange and how does a single rear main seal effect the installation? All marine externals will be installed from 305. The replacement engine will probably be a junk yard dog with a fresh rebuild if needed. Any links to the specific info will be greatly appreciated. I'm looking for cam specs also.

 

[Bondo]

Re: Engine upgrade?

I am looking to the near future replacing my tired salt laden 1984 305SBC with a newer version 350SBC. What specific items must I be aware of when looking at a newer vintage 350, say something in the mid 90's. What parts interchange and how does a single rear main seal effect the installation? All marine externals will be installed from 305. The replacement engine will probably be a junk yard dog with a fresh rebuild if needed. Any links to the specific info will be greatly appreciated. I'm looking for cam specs also.

Ayuh,... You'll need a different flywheel, 'n possibly a different coupler...

 

[series60]

Re: Engine upgrade?

Ayuh,... You'll need a different flywheel, 'n possibly a different coupler...

Is this because of a different bolt pattern on the crank?

 

[Bondo]

Re: Engine upgrade?

Ayuh,... From the rear seal change, 'n smaller crank bolt pattern that comes with it, Yes...

 

[RogersJetboat454]

Re: Engine upgrade?

Mid 90's block will also not have the mechanical fuel pump boss machined (GM stopped machining them roughly around '91). You would need to get a marine electric fuel pump, and would probably be best if it were wired like Mercruiser did for those later motors.

Also need a new intake if you were to get one with Vortec heads. Technically, the intake your '84 has now does not fit standard center bolt heads used from '87 on (middle 4 bolt holes are at the wrong angle), but with a little massage work to open up the middle bolt holes so the bolts will thread in, it can be made to work.

 

[TilliamWe]

Re: Engine upgrade?

..need a new intake if you were to get one with Vortec heads.
Technically, the intake your '84 has now does not fit standard center bolt heads used from '87 on (middle 4 bolt holes are at the wrong angle), but with a little massage work to open up the middle bolt holes so the bolts will thread in, it can be made to work.

Get Vortec heads, you won't be sorry. As Rogers says, you can get an 87-95 vintage motor that doesn't have the Vortec heads, and has the two funny angle intake bolts, but why? Massaging those holes can work, but it can also fail miserably (we tried it once). And the Vortec heads produce so much more power, they are worth it.
Vortec heads came out in 1996 in the marine world, About the same time in trucks. 1997 for sure in Chevy/GMC trucks.

 

[Howard Sterndrive]

Re: Engine upgrade?

another option is to just buy a new GMPP 350/290 crate long block. It is virtually identical to a 1984 Mercruiser 350. $1800 or so and it's brand new. 2 pc rear main seal so you can reuse your coupler. Same fuel pump mounting etc. and will accept your 305's intake manifold if that is reuseable.