Intake manifold

[djmakko1]

87 chris craft 2006 Indmar motor vortec 5.7 stern drive i/o , my motor is in salt water all the time last weekend the intake manifold was bursting water from two plugs that corroded ,the manifold was aluminum.
ive ordered an Intake that will fit my application but it is cast iron, two questions!
1-will it make a difference if it is cast iron when the previous was aluminum?
2- what sealant u use for the section that the gasket won't cover front and back?
your help is always apprciated .

 

[alldodge]

1-It just weights more but should not be a major difference. Might loose some high rpms because the aluminum is probably designed better the the cast iron

2-Mercruise says to place a 5mm bead of black loctite 5900 across both areas and 13mm (1/2) up on intake gasket. This should also work for indmar because they are all GM

 

[Scott Danforth]

1, not really other than it will be 25# heavier, however they make dual alloy manifolds (bronze water passages in an aluminum manifold) which would be preferred.
2, all SBC's use black RTV on the china wall. put a big bead on it, let it skin over for 20 minutes, then install manifold

you may want to check your exhaust manifolds as well. 14 years is way too long a time in salt water.

 

[djmakko1]

1-It just weights more but should not be a major difference. Might loose some high rpms because the aluminum is probably designed better the the cast iron

2-Mercruise says to place a 5mm bead of black loctite 5900 across both areas and 13mm (1/2) up on intake gasket. This should also work for indmar because they are all GM

Should I put the 13 mm on the gasket since the previous didn't have it ? this gaskets have like a raised rubber seam in the middle(blue) in the pic

 

[djmakko1]

1, not really other than it will be 25# heavier, however they make dual alloy manifolds (bronze water passages in an aluminum manifold) which would be preferred.
2, all SBC's use black RTV on the china wall. put a big bead on it, let it skin over for 20 minutes, then install manifold

you may want to check your exhaust manifolds as well. 14 years is way too long a time in salt water.

Thanks, I did check the manifolds early this season since I had a Y pipe also corroded , pull the motor out replace it and changed flappers and did a leak test with acetone, im changing the circulating pump as well just in case 14 years is a lot of time on salt water alright ...

 

[alldodge]

Should I put the 13 mm on the gasket since the previous didn't have it ? this gaskets have like a raised rubber seam in the middle(blue) in the pic

Don't put it on the gasket except where it makes contact. Same as was done before

 

[Scott Danforth]

this is a dual alloy casting. (bronze water passages and aluminum air side)

are you sure it wasnt simply the plugs that failed?

 

[Lou C]

It’s hard to see where the plugs were that failed; were they on the front face of the intake to drain the water passage? I know the later model 4.3 cast iron intakes had a drain plug in that location. Maybe it was galvanic corrosion between the alu manifold and a steel plug. I see no issue using a cast iron intake in fact it might be less prone to intake leaks due to the fact that the heads and intake are the same material. The only thing is you are using a square bore manifold and the cast iron intakes I’ve seen are all a spreadbore design; you might have to use an adapter if using a square bore carb on a spread bore manifold (although Holley does make a spread bore 4bbl).

 

[Scott Danforth]

BTW, a bit of trivia, that intake was made at Buddy Barr castings, the same as Volvo Penta, Ilmor, PCM and Edlebrock and some of the mercruiser intakes.

 

[djmakko1]

this is a dual alloy casting. (bronze water passages and aluminum air side)

are you sure it wasnt simply the plugs that failed?

Yes the plugs fail but the corrosion ate up most of the treads I don't think is fixable

 

[djmakko1]

It’s hard to see where the plugs were that failed; were they on the front face of the intake to drain the water passage? I know the later model 4.3 cast iron intakes had a drain plug in that location. Maybe it was galvanic corrosion between the alu manifold and a steel plug. I see no issue using a cast iron intake in fact it might be less prone to intake leaks due to the fact that the heads and intake are the same material. The only thing is you are using a square bore manifold and the cast iron intakes I’ve seen are all a spreadbore design; you might have to use an adapter if using a square bore carb on a spread bore manifold (although Holley does make a spread bore 4bbl).

I have a holly 4 bbl carburetor and it has the adapter so I think im good there .

 

[Scott Danforth]

That is a fair amount of galvanic corrosion. I am surprised you didnt adress it sooner

 

[djmakko1]

That is a fair amount of galvanic corrosion. I am surprised you didnt adress it sooner

Well, I didn't notice it , the corrosion was covered with the heavy coat of paint it was just like a flake of paint surrounding it until it burst. Now, you mention Galvanic corrosion which means im missing an anode ?? should I install a sacrificial anode somewhere?

 

[alldodge]

This was galvanic corrosion from dissimilar metals. If the plugs were copper or stainless it would happen fast. If they were anything but aluminum it would take longer. The salt helps everything speed up some.

There would be no need for an anode, just watch what is connected.

Are the heads aluminum or cast?

 

[djmakko1]

This was galvanic corrosion from dissimilar metals. If the plugs were copper or stainless it would happen fast. If they were anything but aluminum it would take longer. The salt helps everything speed up some.

There would be no need for an anode, just watch what is connected.

Are the heads aluminum or cast?

Id guess the head will be alloy same material use on intake since motor came from same manufacturer (Indmar ) Michigan Motorz. Just hope won't run into more galvanic corrosion , this motor was installed in 2012 , had the Y pipe corroded the same way now the intake , there's no traces of water in the motor, but now im getting skeptical about this motors are meant for saltwater. I guess is time to get a boat with outboards.

 

[alldodge]

Take a magnet to the head, easy way to find out

 

[Lou C]

I'd be surprised if the heads are aluminum, if so I would have thought that the seller would tell you that you have to install closed cooling....
but I'd tell anyone, even in fresh water, closed cooling at least a half system, is the way to go. It is the one big potential advantage of inboards over outboards besides lower parts cost.

 

[Scott Danforth]

heads should be cast-iron vortecs

if someone installed stainless plugs in the ports, it would have eaten the aluminum and bronze like that. teh plugs should have been bronze.