5.7 Automotive Intake manifold

[AList233]

I'm in the process of gathering the parts to change over my '94 5.7Gi from TBI to Carb.
The cost of marine specific intake is double the cost of an automotive manifold. I understand the marine has brass water passages, but other than that, why couldn't I use an automotive manifold.
The boat is fresh water cooled and only used on inland lakes.

 

[flashback]

I had an automotive AL Edelbrock duel plane on my last boat that lasted me 15 years. The boat rotted and the engine is now in a 85 PU..

 

[Scott Danforth]

Because even in fresh water the manifold will corrode. Not as fast as in salt, however it will still corrode

You can run an auto manifold if you have a heat exchanger

 

[AList233]

Because even in fresh water the manifold will corrode. Not as fast as in salt, however it will still corrode

You can run an auto manifold if you have a heat exchanger

As there is only the water passage supplying the front of the heads, why couldn't I coat the thermostat passage and passages to the heads with an epoxy?

 

[Scott Danforth]

As there is only the water passage supplying the front of the heads, why couldn't I coat the thermostat passage and passages to the heads with an epoxy?

And the block-offs for the back of the head.

I have never found an epoxy to hold up and ended up getting a marine manifold. POR15 used to advertise an epoxy, however their product has been crap since 2008.

Edelbrock (made by Barr castings) has marine manifolds that are nearly identical to the Volvo Penta manifolds and similar to the PCMC manifolds

 

[AList233]

And the block-offs for the back of the head.

I have never found an epoxy to hold up and ended up getting a marine manifold. POR15 used to advertise an epoxy, however their product has been crap since 2008.

Edelbrock (made by Barr castings) has marine manifolds that are nearly identical to the Volvo Penta manifolds and similar to the PCMC manifolds

I have access to some pretty decent epoxies!! POR has been junk for years!
Yeah, but the Edelbrock marine manifold is $575! Just might have to bite the bullet!!

 

[Scott Danforth]

I have access to some pretty decent epoxies!! POR has been junk for years!
Yeah, but the Edelbrock marine manifold is $575! Just might have to bite the bullet!!

Look around, you can find them for less

 

[Bondo]

Ayuh,..... Or go with cast iron, rather than aluminum,....

 

[Lou C]

You can find cast iron used intakes (won't find new for a '94, that should be a pre-vortec 12 bolt unit) on ebay, I found a nice spare for my old pre-vortec 4.3 that way.
If you meant that you have a closed cooling system, then yes you could use an aluminum automotive intake, the corrosion inhibitors in the AF will keep it from corroding

 

[AList233]

Look around, you can find them for less

Tried everyplace I could think of. No luck.

 

[Lou C]

Marine OMC Mercruiser SBC 12 Bolt Intake manifold 14057055 5.0 5.7 350 305 Chevy | eBay

Find many great new & used options and get the best deals for Marine OMC Mercruiser SBC 12 Bolt Intake manifold 14057055 5.0 5.7 350 305 Chevy at the best online prices at eBay! Free shipping for many products!

www.ebay.com

this one needs to be cleaned up but might be OK

Marine OMC Mercruiser SBC 12 Bolt Intake manifold 14057055 5.0 5.7 350 305 Chevy | eBay

Marine OMC Mercruiser SBC 12 Bolt Intake manifold 14057055 5.0 5.7 350 305 Chevy. Condition is "Remanufactured". All our cores are closed system cores with no corrosion what so ever. Call with questions 8609194141Mark Tracking and insurance included in the shipping to the lower 48 We carry all...

www.ebay.com

this one looks good worth the extra $$

 

[Scott Danforth]

Tried everyplace I could think of. No luck.

couldnt have looked too hard - $490 and if you call summit, they will match price

5.0L/305ci - 5.7L/350ci Edlebrock Performance Intake Manifold 2516

Aluminum Performance manifold for 5.0L/305ci & 5.7L/350ci Vortec Marine engines. Intake manifold is secured to heads with 8 bolts. This manifold is a perfect performance upgrade for Mercruiser and Volvo engines with both two and four barrel carburetors.

marineenginedepot.com

 

[Scott Danforth]

just realized, you have a 1986-1995.

 

[AList233]

just realized, you have a 1986-1995.

Yep. Pre-vortec.

 

[Scott Danforth]

I would be tempted to switch to vortec heads since you have to buy an intake. good for an honest 30hp on the 5.7

your looking for the edelbrock 2506 vs the 2516 (vortec)

 

[AList233]

I would be tempted to switch to vortec heads since you have to buy an intake. good for an honest 30hp on the 5.7

your looking for the edelbrock 2506 vs the 2516 (vortec)

I would consider the vortecs if I had a better idea as to how many hours are on the '94 5.7.
I'm leaning towards the Edelbrock 2104 manifold that can be picked up used for around $250 with a Edelbrock 1409 carb.
Thanks for all the advice. It's appreciated!!

 

[Scott Danforth]

boat motors do not wear out. most people panic when they see over 1000 hours. however a properly maintained motor will go over 5000 hours

I would not worry about the hours on the boat. bet if you pulled the heads, you can still feel the cross-hatching with your fingernail.

there are used automotive edelbrock intakes for your motor for $30 on CL and ebay. would not pay $250

 

[Davetowz]

If you are in Ohio I have a couple cast intakes sitting around.

 

[Donald0039]

boat motors do not wear out. most people panic when they see over 1000 hours. however a properly maintained motor will go over 5000 hours

I would not worry about the hours on the boat. bet if you pulled the heads, you can still feel the cross-hatching with your fingernail.

there are used automotive edelbrock intakes for your motor for $30 on CL and ebay. would not pay $250

Most boat engines die of water ingestion.