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Old 02-01-2010, 03:37 AM   #11
Bimmer Heaven
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Join Date: Feb 2002
Location: Ontario
Posts: 15,635
Originally Posted by arsevader View Post
Dunno who told you this but it's baloney.

The secondary air pump is what heat the cats up upon cold starts. That flap doesn't really restrict all that much. Certainly not enough to heat up the cats. A restriction that far upstream that was enough to heat up cats would be a cause for concern.
Not that much, just 50% of the final exhaust size!
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