What does it mean. tried the almighty search but all it turns up is hose related or positive boost threads.

- I am interested b/c I saw someone ask why his car went from -16 to -18 lbs of boost (vacuum) to -14 to -16.

Why does it matter and why should I care?

THANKS

 

He was probably talking about 16-18 inHg, which is inches of mercury (how vacuum is measured). A healthy engine normally runs 16-18 inHg, a lower reading could mean problems, such as a vacuum leak, or a worn out engine.

 

Interesting. Mine seems to run around -15 at idle but dips to -18 or so following changing gears/etc.

At what point is the 16-18 measured?

 

at idle;

BTW: If your's ever goes to 8-10, its time for a rebuild...

 

thanks - is it the same regardless of oil used? Don't know if/how this relates, but I'd imagine if it has something to do with tolerances, it may matter.

 

doesn't the reading depend on elevation?
my car is running fine and it pulls about 12-13 at 3200 ft above sea level. at sea level i get about 14-16 and thats on a stock healthy motor with 40K miles.

 

Anyone have any first-hand experience with this comment? My engine seems otherwise healthy, except for a low vacuum (~10 to 11 in.). If the vacuum is low from a worn out engine, this will show up in a compression test, right?

 

Yeah, I'd like to know too. I have been getting a vacuum of about 12inHg since i bought the car. I have since added the mods in my sig, and did a vacuum replacement, and the idle vac hasn't changed. The car runs really strong, and there's no other detectable problems (boost is perfect). Plus the car has less than 50,000 miles, so I really don't think the engine is dying. I'm wondering what other people have experienced with this.

Oh yeah, i'm also at 7200 ft ASL, so I'm wondering if that is making a difference here.

Rob

 

Altitude, idle RPM, porting, etc. can all have a major effect on idle vacuum. The boost/vac gauges we use are notoriously inaccurate, too.

If the vacuum gauge needle is jumping around a lot at idle, that is a pretty bad sign. But I might get a compression check if the vacuum is just low. Or not. If the car works fine otherwise, I don't think it would bother me too much.

-Max