Manifold Port Question w/pictures

[Vetteman61]

Hello all,

I'm in the process of changing the intake manifold on my 1999 Suburban, 5.7 4x2. It was leaking at the passenger rear. I expected to find a coolant port here, but when I removed the intake I noticed there's no hole here in the intake. Also, I noticed that the intake has two holes in the middle of the mounting surface, but the head has no provisions for these holes.

Is this how these parts are supposed to be made or has someone mismatched these parts at some point? The truck has never run hot. In the pictures below, you can see that on the very rear passenger side there is a coolant port but on the picture of the manifold, there is not and reverse for the holes in the middle of the intake.

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I hope to reinstall this early tomorrow and I certainly don't want to install this to find that it is incorrect and have to do this all over again.

Thanks in advance for the help,

Brandon

 

[SAATR]

All factory stuff there, no worries.

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[Vetteman61]

Thanks, I'm glad to hear it. What was the purpose of casing those ports if they aren't used. My guess was multiple application uses.

 

[SAATR]

SBC cylinder heads have always had coolant ports at the front and rear of the heads, though the rear ports are generally not present in the manifold. It could be that they wanted to be consistent with the old architecture, or that they wanted the option for a rear crossover should they decide to use it. The holes in the intake serve no purpose that I'm aware of, and could simply be to lighten the intake and make it cheaper by removing metal where it isn't needed. It could be something for locating the rough cast intake on a machining fixture at the production facility. Lots of possibilities.

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[Vetteman61]

Since this rear area is so prone to leaking could one weld the hole shut in the head, rather than sealing it with the gasket and intake and solve the problem once and for all?

 

[slowburb]

When properly "gasketed" and torqued, there are no leaking issues from an L31 intake manifold.

 

[someotherguy]

The heads are cast that way because SBC heads can be used on either side.

I believe there was another reason for the rear coolant ports but I can't remember.

Richard

 

[FastOrange]

all SBC have the rear ports. some do use them (87-95 TBI for example), i have seen old carb intakes that use them too.

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[Vetteman61]

Interesting info. Thanks for the replies.

 

[slowburb]

FYI - use of any other gasket but the Fel Pro MS98000T will result in coolant leak.