Exhaust manifold gasket placement

[Louie C.]

Been down this road too many times to remember. Building small block for a driver. Which side of the exhaust gasket goes next to the head, the metal side or the fiber gasket side? Trying to get around milling the manifolds flat. They look in tolerance though

[Joe L.]

Re: Exhaust manifold gasket placement

Been down this road too many times to remember. Building small block for a driver. Which side of the exhaust gasket goes next to the head, the metal side or the fiber gasket side? Trying to get around milling the manifolds flat. They look in tolerance though

Louie-----


I don't know what sort of manifold gaskets you have. The ones I have seen over the years have the foil shielding on both sides of the gaskets and can be installed either way. I'd be reluctant to use any gasket that was not foil shielded on BOTH sides.

[Stuart F.]

Re: Exhaust manifold gasket placement

Pardon my ignorance, but what small block/exhaust manifold bolt up uses gaskets? I know you can get them, specially for headers, but aren't they (stock) usually applied metal to metal? What am I missing?

Stu Fox

[Bruce B.]

Re: Exhaust manifold gasket placement

According to FelPro, the steel face goes against the manifold and the fiber against the engine block.

[Joe L.]

Re: Exhaust manifold gasket placement

Pardon my ignorance, but what small block/exhaust manifold bolt up uses gaskets? I know you can get them, specially for headers, but aren't they (stock) usually applied metal to metal? What am I missing?

Stu Fox

Stu-----


No Chevrolet small block or big block through 1979 ORIGINALLY used any sort of exhaust manifold gasket. However, gaskets are supplied in various GM gasket kits for SERVICE use in order to "compensate" for slight manifold warpage that might cause an exhaust leak. 99.99% or more of the folks that have an engine rebuilt don't care, at all, about "correctness" and are MUCH more concerned about having no exhaust leaks (which can be hazardous to your health).

[Stuart F.]

Re: Exhaust manifold gasket placement

Joe;

I whole heartedly agree, and thanks for your reply. I can't begin to say how many times I've taken used manifolds off and put them back on again w/o gaskets, and can't recall ever having a leak. If I was at all concerned it was with the outlets. I've had a few of those leak, specially those on the old two stud "log" types (55 & 56). I've dealt with some "cookers" too that would turn the manifolds cherry red. One need only do a few IR gun checks after a drive to realize what the manifolds go through. Ain't nuthin hotter under the hood.

I suppose the true restorer would check the manifolds and mill them true if they were suspect.

Stu fox

[Louie C.]

Re: Exhaust manifold gasket placement

Thanks Bruce, that is the info I needed

[Jim T.]

Re: Exhaust manifold gasket placement

Some C4's use exhaust gaskets. Don't know the years that C4's used them, it may of been only the aluminum headed C4's. My GM C4 parts book only goes to 1989 or 90. I used a set in 1994 when I installed my GM ZZ crate engine in my 70, it has aluminum heads like the C4's. My 70's original exhaust manifolds did not leak on my original heads but there was a very small leak with the aluminum heads, the C4 exhaust gaskets fixed that. Still doing a great job.

[James W.]

Re: Exhaust manifold gasket placement

Stu,

Be aware that when exhaust manifolds are milled to remove warpage they tend to warp easier. Sometimes it has to be done, but I would advise anyone doing it to be cautious and remove the minimum amount of metal

Jim

[Joe L.]

Re: Exhaust manifold gasket placement

Stu,

......... be cautious and remove the minimum amount of metal

Jim

Jim------


That's the key. You don't want the machinist to be taking a "big whack" off the manifold surface because that's the easiest thing to do. Only 2-10 thousandths will be necessary in most cases and that won't significantly affect the future durability of the manifold.

[Joe L.]

Re: Exhaust manifold gasket placement

Some C4's use exhaust gaskets. Don't know the years that C4's used them, it may of been only the aluminum headed C4's. My GM C4 parts book only goes to 1989 or 90. I used a set in 1994 when I installed my GM ZZ crate engine in my 70, it has aluminum heads like the C4's. My 70's original exhaust manifolds did not leak on my original heads but there was a very small leak with the aluminum heads, the C4 exhaust gaskets fixed that. Still doing a great job.

Jim-----

All C4's used gaskets between the manifolds and cylinder heads. This includes all 1984 to 1991 as well as 90-95 LT-5 and 1992-96 Gen II small blocks (LT1 and LT4).

C5 and, I believe, C6 Corvettes also use gaskets.

The C4's were not the first Corvettes to use gaskets between the exhaust manifold and the cylinder head, though. That honor goes to 1980 Corvettes with the California-only LG4 (305 cid). They were the first Corvettes to use tubular exhaust manifolds and the first to use gaskets. All 1981-82 C3 used gaskets, too, since they also used tubular manifolds.

[Terry M.]

Re: Exhaust manifold gasket placement

Jim-----
1992-96 Gen II small blocks (LT1 and LT4) did not use gaskets since they went back to cast iron manifolds.

Gee, Joe. Here is another difference between the LT1s in the B & Y body. B (and I think D) bodies got exhaust manifold gaskets -- very nice ones I might add. Cast iron HEADS and exhaust manifolds for the B & D boduies, so maybe the head material made the difference. Then there is the awful design of the exhaust manifold fasteners. They snap off inside the head. Fixing them is SO much fun.

C5 and, I believe, C6 Corvettes also use gaskets.

Now you are goign to make me look at the new (relatively) car.

[Bill C.]

Re: Exhaust manifold gasket placement

IMO it is very important to be sure the exhaust manifolds seal properly against the head WITHOUT gaskets.

A good machinist can remove the minimum required, the manifold needs to be seated against the head in order to tranfer the heat building in it to the head and into the cooling system. With the bolts tightened properly with the french locks installed the manifold will run much, much cooler, probably will not warp again as it runs so much cooler and without the massive temp swings. Under hood temps will be lower also!

I think the gaskets are included in the kits because people wanted them, thought they needed them, trying to seal bad fits.

The gaskets are always made of asbestos or similar material which is an excellent heat transfer insulator

With that gasket in place there is no where for all that heat building up to go other than the surrounding air so it will quickly reach exhaust gas temp and thats HOT, to hot. Then it cools, then gets real hot again, and very quickly warps again.

[Joe L.]

Re: Exhaust manifold gasket placement

Gee, Joe. Here is another difference between the LT1s in the B & Y body. B (and I think D) bodies got exhaust manifold gaskets -- very nice ones I might add. Cast iron HEADS and exhaust manifolds for the B & D boduies, so maybe the head material made the difference. Then there is the awful design of the exhaust manifold fasteners. They snap off inside the head. Fixing them is SO much fun.

Terry-----


I was incorrect about the 92-96 LT1 and LT4 not using a gasket. They did use a gasket----GM #12552470. It's probably the same one used on the other LT1 applications. I'll correct my previous post so that confusion is not created in the future for someone that searches on it.

[Stuart F.]

Re: Exhaust manifold gasket placement

The point about heat transfer is very interesting. I often check my exhaust manifold temps after a drive and b4 shutdown (63 L-76), and usually see about 525 to 560 degrees above the outlets. The R.H. side always seems to be running hotter than the L.H., with or without the heat riser butterfly wired open. I don't know what I am looking for or what they should be, other than I was looking for any changes or trends while I was making carburetor changes during my percolation problems this past summer.

Does anyone have any spec data or theories on what these temps should be and, if extreme or out of line, what could the cause be, etc.

Hope this isn't deviating too far off the subject of the thread.

Stu Fox