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      05-25-2012, 10:46 AM   #9
MilehighM3
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Drives: E90 M3
Join Date: May 2011
Location: Colorado Springs

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The stock manifold has a tapered collar on it that holds the o ring gaskets in place. As you tighten it down, they are forced on to the larger end of the taper and seal outward against the head. I think I recall seeing this tapered sleeve on the inside of the single manifolds? Not positive on that though.