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Anyone heard of cutting expansion lines between header flanges to prevent leaks?


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Hi everyone,

I recently heard of a technique some folks have used to prevent header flange leaks on our L-series engines. The technique is simply cutting the flanges apart in between each tube's mounting bolt holes. This gives the metal somewhere to go when it expands, as I was advised that sometimes as the header flange expands it will bow and create leaks. I heard this from a couple of z-car racers at a race day at Blackhawk Raceway in Wisconsin (I asked them if they were members of our forum, none of them were).

I don't know if this is a race-only technique that might weaken a header that needs to put up with longer-term use, or if the technique was even still valid for modern aftermarket parts. It may have been an old technique. Anyone have experience with it? I have an MSA 6-1 header, not yet installed, that eventually will go on my car, so I figured I'd ask about it and make the modification before installation if it turns out to be useful. Thanks, everyone!

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A Z racer at Blackhawk source might be Phil Reith. He would know.. I had mine Jet-Hot coated which is supposed to move the heat along and mitigate some of that. If it's any consolation, when I arrived in California I discovered that many of the factory exhaust manifolds in the Pick and Pull were warped as well.

I have also heard of having the mating surface milled to make it perfectly flat.

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Guys used to do this on small block chevy headers if the flanges were not very thick. The thinking behind it was the same as you presented above to keep them from warping. However the flange on my MSA coated header is very thick and I believe if torqued correctly should not require any cutting of the flange between the primary tubes. I would vote to install it as-is, torque it correctly, and see what happens. Worst case if it is does warp its not that big of a deal to pull off.

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