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What's a normal Engine Vacuum Pressure?

posted by  745 TurboGreasel on  Mon Oct 20 21:37 CST 2003
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In sort: No
the long:

The ASE (Automotive Society of Engineers) considers 17-21" and to be a good reading at idle. You want to see 0 at full throttle.

There are a great many things besides compression which affect your readings:
air cleaner cleanliness (and brand)
ignition timing
idle speed
fuel mixture
vacuum leaks
cam timing
cam lobe overlap/profile
exhaust restriction

Generaly a higher and more even reading indicates better running and or higher efficiency.

Low speed torquey motors will usualy have higher vacuum...
Full race motors often do not make more than 12", and will not properly operate vacuum brake boosters and the like.

You can find an article which covers the basics of using a vacuum guage for engine diagnostics here: http://autorepair.about.com/library/weekly/aa112401a.htm





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