Whats a normal vacuum reading?

[OonDeanisS]

I just installed my vacuum/boost gauge and my car idles at about 15, drops to about 12 when i step on the gas, and then goes to like 22-25 real quickly until i let off the gas. (this is in neutral).... so is this normal and good? The car runs fine as far as i can tell.

 

[vristang]

Sounds about right to me.

I get about 14" at cold start idle, and about 16" when the motor gets hot.
I will get about 25" or more if I come off the throttle quickly. (this is when driving and in gear)
At wot my reading is near 0".

The numbers will vary depending on displacement, camshaft, tb size, etc.

 

[90mustangGT]

10" is considered normal at idle, and should increase at 2500rpm or so, until you hit the gas. The reading should be stable. Vacuum should stay stable at the same rpm same throttle.

 

[v8only]

10" is considered normal at idle, and should increase at 2500rpm or so, until you hit the gas. The reading should be stable. Vacuum should stay stable at the same rpm same throttle.

15 to 18 is normal with a stable reading. at ten inches of vacuum on a stock motor at idle, you've got some serious problems.

 

[HISSIN50]

Yep, 18-20 is good for a stock cam. I would freak with any cam at 12" hg or less.

Crudely stated, manifold vac reading is inversely proportionate to throttle opening.

 

[v8only]

I've got 12 to 13, slightly wavering, and the car runs like complete ass (my explorer drop in) throwing codes for ect, map, and everything, but I think it's unrelated. Stock cam, idle like ass, bad vacuum. Damn I'm sick of this. But, as just explained, that's my experience with bad vacuum this weekend. In my case, I think my low vacuum is from the engine running like ass.

 

[HISSIN50]

Jeremy, if you could ever scrape together even a few hours in a row to work on it, I bet you could get it running like a champ. I know you are super busy though. Good luck with it.

 

[v8only]

we worked on it for many hours this saturday. Oh well I just want to get her running, dialed in, and race it a few times, and cruise it for the next year.

I've got an 06/07 mustang gt in the plans within the next year, and will sell my 86gt vert of 10+ years at that point.

 

[OonDeanisS]

thanks everyone

 

[Sicarius428]

Really depends on your cam. For a stock cam with no leaks you should be around 20hg. I have an E cam with 130K miles on the engine and am pulling 14ish.
Kevin