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Click on image for the lowdown. 
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Mod | | | Forums66 Topics128,104 Posts1,056,197 Members48,436 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
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For helping keep this great
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on the Internet for over 30 years! and not clogged down
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| | | | Joined: Mar 2002 Posts: 9,115 'Bolter | | 'Bolter Joined: Mar 2002 Posts: 9,115 | The vacuum pump delivers a smaller vacuum than the manifold. It is meant to augment the vacuum when it is low in the manifold. The pump will not deliver a lot of vacuum at low RPMs. At least, that is how GM explains it. I think when I had mine it would deliver about 11" at a higher RPM. | | |
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