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What Is The Right Figure Here

Devils_Advocate21
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Devils_Advocate21 Mentor

Devils_Advocate21

Posted
Posted

How would i determine if i have a vacuum leak at idle. What would an appropriate mmhg figure and vac figure be at idle if i had a small leak.

IE: anything greater than 20 mmhg say like 27 mmhg would mean i have a leak or anything closer to positive booost so say 15 mmhg would mean i would have a vac leak.

Cheers guys

A

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blind_elk Grand Master

blind_elk

Posted
Posted

Engine vacuum is measuring the vacuum in the plenum. As you open the throttle, vacuum decreases (pressure moves closer too 0 (atmospheric) pressure). So, I'm thinking that unless the air is leaking directly into the manifold / plenum, you will not detect an air leak by observing idle vacuum.

MBS206 Grand Master

MBS206

Posted
Posted

If searching for a vacuum leak, then he would find one by observing it Blind Elk. But the leak would have to be on the motor side of the throttle body.

Finding an inlet leak is ALOT harder.

My car, stage one modded (FMIC, Exhaust pod filter+Box), sits at 20mmHg, but if I flick the air con on, so that the motor can idle with a moderate load, it opens the AAC (Allows in more air like a "leak") and it then sits on 18mmHg.

But then again, a change in cams (To a big set) and your idle vacuum can be as little as 5-10mmHg

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