Boosting?

[Andrewsmc]

Just curious what my guage should read when car is shut off, And what my vac reading should be at idle?

[crashkelly]

Just curious what my guage should read when car is shut off, And what my vac reading should be at idle?

should read 0 when off...should be 22hg or 24hg(if the a/c is on) while running

[peajay]

a good idle vac with no a/c is 21. ideally you always want more than 19

[orng1]

The higher the better, I get 23ish when I have been driving the car but after a few days of sitting it will be 20ish for a few miles or so.

[Andrewsmc]

and. what exactly is Vac? i know its vacume but whats it mean? any other threas to direct me to? and can i adjust my guage? when its off it reads neg 2

[peajay]

depending on your gauge you may be able to adj. it but its a pain and honestly it would be better in the long run to just get a higher quality gauge. there is a big debate over elec. or mechanical. personally i like mechanical, but you will find what you like.
vacuum is basically negative pressure in your intake manifold from your pistons pulling air in and your throttle plate restricting more air from entering. i dunno if that made as much sense as i planned it to have....
regardless, its a great tell tale to the state of your engine's internals. any problem, be it bent rods or burnt valves or leaking rings you will be able to tell by your vacuum gauge. If you have good vacuum you have a healthy engine! basically you want a steady needle at all readings, if the needle bounces around meaning that it's not smooth in it;s travel you either have a shitty gauge (which, pardon me, but you may just have) or internal engine trouble.

[fatti03msp]

This stuff is all latin to me, but are stewart warner good gauges, cause that is what was in my car when i got.

[1moreMPH]

michael -- between 20-22 vac at idle is ideal. i guess higher could be because of upgraded exhaust mani or free exhaust, but im not sure and ive never heard of it being a good thing. with AC on, mine goes to ~17 vac, but i never drive with AC on.

it should def. read 0 when turned off. You should be able to send it to the company to get re-dialed so check into that. Or there may be a kink in the line (runs thru firewall to the intake mani)

1st lesson in thermodynamics: for a fluid to move there must be a difference in pressure in a given volumetric system. The system is from your intake, to your cylinders. Gas is pushed out of the cylinders by the piston after combustion, which is then lifted back up creating a vacuum to suck air back into the cylinder for combustion. There must be a vacuum (or boost for that matter) for the air to move into the cylinders, and this is what your gauge is reading, measured from the intake mani just before it enters the combustion chamber.