Need help with Pontiac 400 6x heads

[agood1]

I have a street rod with a Pontiac 400 1975 model....the heads are marked 6X. I pulled the intake to get it powder coated and re-installed it...I noticed a port right in the center of each head that was not getting covered by the intake when I re-installed it....I looked at it and figured it was just a empty casting hole and did not go anywhere....well, I was wrong....after I get it back together...I found that coolant would flow from these holes at higher RPMs....So the question is....how do I cover these holes if the intake does not cover them....

Thanks
Brian

[MagicRat]

What was covering that port before you took the manifold off?
Is the manifold installed backwards?

It might be possible this intake was designed to run dry, that is to not have coolant circulate in it. If this is the case, it may have used an intake gasket designed to 'block off' the coolant passage. I do not know if such an item is available.
However, running a street engine with no coolant heat sounds like a recipe for carburetor icing, so I could be wrong on that.

You might be able to fabricate a tiny block off plate and braze it into place, over the coolant passage.

[agood1]

Not sure what if anything was covering the port. the manifold cannot go on backwards....because it has a coolant passage in the front that connects directly to the water pump....wierd design and leaks...but none the less it will only mount one way. I am sure coolant must flow thru the manifold becuase it would not reach the thermostat if it did not...which is mounted on the top of the manifold.

[MagicRat]

Of course coolant flows through the front of the manifold to the rad hose. But that is included in all Pontiac manifolds, including the "dry" ones.

In most intake manifolds, coolant circulates below the carb and along the intake runners. This warms the runners and helps keep the fuel/air mixture in suspension.

However, some intake manifolds are 'dry' and keep the fuel/air mixture as cool as possible for max power, by eliminating this warming coolant.

This may work on a race track on a warm sunny day, but for all-around use, including cold weather driving, a "wet" manifold is better.

These center coolant ports are required for a 'wet' manifold, but are not required for a 'dry' type.

[agood1]

OK, I guess the question is...what are these ports in the center of the heads actually for...if they are for coolant then there is something wrong with my manifold...because these ports are exposed even with the manifold installed. I am going to try and post some pix.

[agood1]

[agood1]

So should that port be exposed like that?

[MrPbody]

First, those are simple cavities going nowhere. Their purpose is open for debate, but most surmise they are there to make installing a non-EGR intake (pre-73) difficult. They exist only on '73-later heads.
Brian, you have e-mailed me directly over this matter. There is no coolant at those cavities unless there's a crack in the head (very rare). There is only coolant at the front (in the intake), where the crossover for the thermostat lives. If you have coolant loss at the middle, something is terribly wrong. The pics show only the "normal" stuff. yes, the cavities SHOULD be open like that.

"Performer" is Edelbrock's replacement intake for mild performance Pontiacs.

[MagicRat]

Thank you for the input. I stand corrected.

[69GTO]

Originally Posted by MagicRat

Thank you for the input. I stand corrected.

years ago Mr. Gasket used to make a intake kit which included a metal plate that covered the holes of which you speak I used to use them for mine not sure if they are made any more or not though.

It seems to be the exhaust cross over, the steel plates were to block the exhaust from going into the intake to warm up the intake mix for cold weather.

I have gotten SBC plates to work, but it's to easy to make your own.

I think Mr. P is right, sounds like a crack or a blown head gasket, as I don't think that even the green would leak that much from the water cross over.

You could bolt on an intake backwards if the water cross over was cut off, as many Pontiac people do cut them off.

As for the pic P body is right so may people have talked about why this was like that, I like to think it had to do with future ideas that never made it.

Good luck.

[hotrod_chevyz]

Sorry to dig up an old thread, but those are called steam holes. They are meant to be there covering them will only hurt. They were put there to prevent pockets of steam inside the engine causing it to overheat. If you have a leak coming from them,Then the head gaskets you used werent exactly right, or you have a difference in years between the heads and block. You might have to use a proper head gasket as a template, and possibly drill additional coolant passages in the block deck or head itself in order to match the heads to the block. if you need some passages covered to fix the leak, you might have to go to a different year or type of head gasket.

T

[MrPbody]

HotrodChevyZ,

There's only one head gasket for 400 Pontiac, regardless of year. The cavities over the crossover are there to make it difficult to install a non-EGR intake on EGR heads. There are no "steam holes" in Pontiacs. You're confusing them with small block Chevys...

Jim

[hotrod_chevyz]

Jim:

SRY thats just what i was told by my boss up at a shop where i used to work. I asked about them as I was tinkering around with my Catalina's 400 one day at work before i even owned it. He said it was a revision to keep the block or heads from messing up between cylinders 3 & 5, and 4 & 6. he's like 60 years old and has owned the shop for 25 years, so i took him on his word. Like you said open to debate, but thats not why i posted. Ive had problems in that arena before and thought i could maybe help anyone reading this thread looking for a cure to the same exact problem.


Depending on the bore of the engine, and the quality of the gasket you expect, and if your putting aluminum heads on a cast block, it would probably be hard to count all the different head gaskets you can get for a Pontiac 400. And its pretty easy to purchase the wrong ones if you dont know what your looking for. The quality of the gasket, the compressed thickness, as well as some heads have small water holes, some do not. And if you have a pre 67' 400, a lot of head gaskets (post 67 design) will not work on them. And when or if your putting together a bastard motor, it makes it even harder to chose wich gasket you need. Some gaskets are even sensative to the type of machine that surfaced the deck of the block, meaning SSG machine or others. Once again sry for digging up an obviously dead thread. Time to put the shovel down. Peace.

T

[gmtech 78]

I have a pontiac 400 as well and those holes are supposed to be there. They are there to seperate and keep the oil under the valve covers from getting hot and allow a air gap between the exhaust crossover port. The upper port can be filled with funace cement and sanded flush then you will be able to use any year intake and gasket on your 6x heads there is a article in january 2013 in high performance pontiac about how to do this.