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Thread: manifold passage

  1. #1

    manifold passage

    I have posted this on 3 other forums in the last few days. Out of the literally hundreds of people who've viewed it, only 2 replied. This still remains unanswered.

    The photos below are generic, the lower intake manifold and plenum of a late-model 4.3 Vortec. I don't have a manifold in my hands to examine, so I'm working from photos for the time being. I'm trying to find out the purpose of the passage in the manifold that's circled in yellow. It's sealed off from the intake air inside the plenum, and it vents to the atmosphere through the hole in the plenum also circled in yellow. It doesn't connect to intake air, coolant, or oil, but since there's a hole specifically molded for it in the plenum, it must have some definite purpose. Anybody know what it's for?

    Screenshot 2022-07-01 200618.jpg

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