SBC intake manifold gaskets.

[Clone TIE Pilot]

I suspect my intake manifold gaskets may be leaking vacuum. Currently I have a ZZ4 intake on my L69 305. GM recommends PN 10147994 gaskets which are coated and embossed steel shim gaskets. However, I recently read that it is generally recommended not to use steel gaskets with aluminum intakes. A few years ago I had Fel Pro 1256 printoseal intake gaskets, but they leaked vacuum due to not having sealing beads for the EGR ports. The GM gaskets do have embossed seals for the EGR ports. Moreover, a company called Magnum makes a version of printoseal style intake gaskets that do have printed seals for the EGR ports, MS18010.

In short, I am not sure if GM's recommendation is correct about using steel gaskets with their aluninum ZZ4 intakes? The intake is torqued to 30 ft/lb.

 

[ELCAM]

Not understanding the vacuum leak at the exhaust crossover passage. Does it leak exhaust or vacuum or both?

Searching that GM part number i find fiber gaskets never seen metal intake gaskets.

Did you torque it in the proper sequence? If you torque the ends first it leaves a bulge in the middle and often will not seal.

 

[Clone TIE Pilot]

Not understanding the vacuum leak at the exhaust crossover passage. Does it leak exhaust or vacuum or both?

Searching that GM part number i find fiber gaskets never seen metal intake gaskets.

Did you torque it in the proper sequence? If you torque the ends first it leaves a bulge in the middle and often will not seal.

The two EGR ports are separate from the heat crossover ports. One is a vacuum passageway to the EGR, the other is a connecting passageway from the heat crossover to the EGR valve. Both of these EGR ports are blind ports with no mating port on the head, they are there simply for removing casting sand from the internal EGR passageways. However, these blind ports still must be sealed to prevent vacuum leaks, both adjoin the 6th cylinder intake port. Basically an EGR equipped non Vortec SBC intake has 8 intake ports, two coolant ports, two blind coolant ports, two heat crossover ports, and two EGR ports, 16 ports in total.

 

[ELCAM]

Thanks for the pic. Makes much more sense now. There is not a lot of metal between the one port and the number 6 intake port.

One thing i do see is there are different intake port widths. Some gasket sets are listed by size such as the MAHLE 95070SG with 1.28 inch wide ports or the MAHLE 95128SG with a 1.23 inch wide port.

Wonder if some are just generic gasket sets and are made to the widest port width (with + or - tolerances what that could make it worse.). I would measure the port width of the gaskets you are having problems with and see if they are the big one. If so try the smaller port sets.

Edited to add:
Looking for dimensions on other gasket sets and having little luck.

My opinion is use non printed gaskets and glue it to the intake manifold with copper gasket adhesive, making sure the gasket is 100% covering the problem area (no misalignment with the intake port).

 

[Clone TIE Pilot]

Forgot to say I did follow GM's torque sequence and didn't use the China wall gaskets, just a bead of RTV.

These are the metal GM gaskets I currently have in the engine which I am concerned are leaking. They are steel shim with a grey coating that makes them look like fiber or paper. You can see they have embossed seals for the two EGR ports.

Here are the Fel Pro Printoseals I had before and you can see they are missing the EGR port seals.

Here are the Magnum MS 18010 printed seal gaskets that do feature EGR seals.

 

[64nailhead]

I wouldn’t consider a shim style intake gasket on an aluminum intake. Felpro1204, 1205 or 1206 depending on your intake port dimensions.
And definitely a bead of silicone in the China walls.

 

[wingnutks]

Get the 1204/1205 S-3 gasket. It is the same fiber paper stuff with the printo seal on it, but it has a metal shim inside to stop it from distorting. I have used a standard felpro and edelbrock and they both eventually started leaking vacuum. There is very little meat between the ports of a sbc... over time under high vacuum/boost they distort and pull into one port or the other and leak vacuum/boost/oil. I have the 1206 S-3 in my car now and they have held up great and I have even re-used them after taking the intake off to re-seal the front china wall, and they still are doing good.
If you get the standard .060 thickness ones, put everything on dry and check your front and rear rail gaps to make sure you have some clearance there for when you tighten down the intake it doesnt bottom out there first.

 

[Clone TIE Pilot]

I would like to get steel core version of Fel Pro's printoseals but they don't seem to offer any version that has sealing beads for the EGR ports by the 6th cylinder. Guess I will go with Magnum's version of printoseals as they do have beads for the EGR ports.