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post #1 of 7 (permalink) Old 03-06-2006, 05:56 PM Thread Starter
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Negative Boost

Can someone explain to me why boost gauges operate in negative boost. If the + side is psi above atmospheric pressure then is negative below atmospheric pressure. So is it true that naturally aspirated engines operate at atmospheric pressure or 0 on a boost gauge.

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post #2 of 7 (permalink) Old 03-06-2006, 05:58 PM
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dont you mean vacuum?




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post #3 of 7 (permalink) Old 03-06-2006, 06:57 PM
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A naturally aspirated engine operates at 'negative boost', or vacuum. If it didn't, it wouldn't 'suck' any air into the engine.

A supercharger, or turbo forces more air into the engine than it would draw by itself, thus creating 'boost'.

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post #4 of 7 (permalink) Old 03-06-2006, 08:20 PM
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If an NA engine is not showing a vacuum when its running then you either have a REALLY big problem or you have the gauge hooked up to the wrong end of the engine.

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post #5 of 7 (permalink) Old 03-22-2006, 08:24 PM
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actually you should be reading 18-22 in Hg (inches of mercury) at 2000 rpm on manifold vacum (below the throotle plates) using a vacum gauge hooked up to a good source (i like the brake booster)

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post #6 of 7 (permalink) Old 03-22-2006, 08:45 PM
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Normal outside pressure at sea level with a temp of 70F you should be at 29.92 HG (inches of mercury) which is the standard. The metric equivalent is 1013 millibars. One Bar is equal to one atmosphere which is 14.7lbs per sq in. Damn the crap you remember LOL

An engine is an air pump so you should think of it in that way.

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Last edited by Mark M. TCCoA VP; 03-22-2006 at 08:56 PM.
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post #7 of 7 (permalink) Old 03-23-2006, 03:12 PM
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Quote:
Originally Posted by greencurse
actually you should be reading 18-22 in Hg (inches of mercury) at 2000 rpm on manifold vacum (below the throotle plates) using a vacum gauge hooked up to a good source (i like the brake booster)

-greencurse

right on...mine is right at 18 to 18.5 at 2k RMP....

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