Which base gasket?
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
It depends on the year of your manifold and its configuration. Most will use the top gasket, which is a 1/4" thick gasket.
The bottom gasket is one gasket in a 3-part gasket "stack" that was used in 68 and 69 on intake manifolds utilizing an exhaust groove crossover that runs just in front of the primary throttle bores. If you have the exhaust groove "smiley face" running just forward of the primary bores, you have to use a composite hi temp gasket with the matching groove, following by a stainless steel reflective shield, and then the gasket you have pictured in your lower photo goes on top of that again. That gasket is never used by itself.
The bottom gasket is one gasket in a 3-part gasket "stack" that was used in 68 and 69 on intake manifolds utilizing an exhaust groove crossover that runs just in front of the primary throttle bores. If you have the exhaust groove "smiley face" running just forward of the primary bores, you have to use a composite hi temp gasket with the matching groove, following by a stainless steel reflective shield, and then the gasket you have pictured in your lower photo goes on top of that again. That gasket is never used by itself.
