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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,265
If the motor is stock 7:1 compression in good tune and fully warmed up idleing about 800rpms manifold vacuum at sea level it will be around 12-13 inches of vacuum or about 13hg for inches of mercury in a skinny vertical glass tube which is what they used to measure vacuum before round gauges with needle pointers were invented.

A 7:1 compression normally aspiriratd motor is extremely inefficiant but it is that low so you can run alot of turbo boost in these old 2 valve hemi combustion chamber air cooled heads.

By contrast a healthy motor with 10:1 compression will idle at around 20-21" of vacuum because with that compression each power stroke makes alot more heat and power with the same amount of air and fuel in the combustion chamber after the intake stroke.
Old 08-18-2011, 05:49 AM
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