I have a 1972 Z that continues to blow out the 2 holed gasket between the manifold and the down-pipe and leak.  I've tried both cut rate auto parts store versions and the OEM version with equal success. The motor is mildly built and I'm running a single 2 -1/2 inch exhaust from the down-pipe to the rear. Wondering if exhaust dope might possibly help. Anyone else have a similar problem and found a solution.

Is it possible something is causing too much back pressure or excessively high exhaust temps?

Not likely, I run consistently 180-190 degrees and am running 2-1/2 exhaust and straight through glass pack muffler

I'm at a loss

 Are the two mating flanges parallel to each other before bolting them together?

I will double check the mating surfaces. I have two more gaskets coming next week so will try again. Arghhhh!

@Randalla I discovered that the flange on my original down pipe was no longer flat after fighting the same issue for a couple years. Using two gaskets helped for a while. Ultimately i purchased a new down pipe and had it mated to my new Zstory exhaust then ceramic coated it and the manifold. Problem solved. Good luck. 

Try the gasket with a film of red RTV on all four surfaces (manifold side, gasket to manifold, gasket side to down pipe and the down pipe surface). Should fill in any gaps. Haven't used an exhaust/intake gasket in over 15 years. That's about 12 times I have installed/removed a header/intake as I've swapped in different engines on both the street and race car.

 

 

 

 

I used to get a McChord brand gasket that came with red silicone on it. Can’t find them anymore, so getting a plain gasket and coating it with red RTV should work. 
 

I found the stock head pipe flange to be too thin, and it would deform, and then leak. So I made my own from 3/8” flatbar, then made my own headpipes. 
 

No leaks.
 

This got started because I was running a production class and had to run the stock manifold. The engine produces a lot of heat when racing, the manifold and head pipe get cherry red.

 

Edited October 16, 20204 yr by Racer X