What Is The Right Figure Here

[Devils_Advocate21]

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

[GTS-t VSPEC]

The vacuum at idle can depend on lots of things, including mods, so I'm not sure the actual number will really give you the info your after.

[blind_elk]

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]

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

[WogsRus]

well mine is 16-18 mm HG, depending on how it starts. LOL.

According to manual, the stock skyline is suppose to have 17-20 mmHg.