What are people here seeing for vacuum pressure at idle?
09-10-2006, 05:56 AM
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seems a little high for this altitude doesn't it?
The reason I bring this up is that I cannot seem to get any more pull than 16.5 inches ( I've verified this using a seperate vacuum gauge hooked directly to the engine to verify my boost/vacuum gague was correct), and I did a great deal of reading about barometric pressure etc and vacuum. I've also extensively vacuum checked/ pressure checked my whole system and found nothing to attribute a leak of any sorts.
Here in Denver there usually isn't more than 24.5~25.00 in HG of atmospheric pressure, and when you are idling or decelerating your engine is serving almost as a vacuum pump and because of the reduced pressure there should be a reduction of vacuum pressure both at idle and during decel. For example if you lived on the coast and during decel you saw 23.5 in HG then that would be normal, but that would be very close to a perfect vacuum here in Denver, and would probably shut off your car. Moreover, even with your foot off the pedal the throttle plate is slightly open, which in essence is a controlled air leak so far as vacuum is concerned.
Our engines can only draw so much air, rated as a percentage of total possible vacuum, (for 1.8T's at sea level that seems to be around 65~70 percent) so given our reduced atmospheric pressure the engine should still only draw 65~70 % of the overall atmospheric pressure, giving us a lower total number.
25 x 0.65 = 16.25 in Hg
25 x 0.70 = 17.5 in HG
I am almost willing to bet those of you seeing say more than 18 have gauges that may be slightly off, less than .5 psi (or 1 in HG)
thoughts?
Here in Denver there usually isn't more than 24.5~25.00 in HG of atmospheric pressure, and when you are idling or decelerating your engine is serving almost as a vacuum pump and because of the reduced pressure there should be a reduction of vacuum pressure both at idle and during decel. For example if you lived on the coast and during decel you saw 23.5 in HG then that would be normal, but that would be very close to a perfect vacuum here in Denver, and would probably shut off your car. Moreover, even with your foot off the pedal the throttle plate is slightly open, which in essence is a controlled air leak so far as vacuum is concerned.
Our engines can only draw so much air, rated as a percentage of total possible vacuum, (for 1.8T's at sea level that seems to be around 65~70 percent) so given our reduced atmospheric pressure the engine should still only draw 65~70 % of the overall atmospheric pressure, giving us a lower total number.
25 x 0.65 = 16.25 in Hg
25 x 0.70 = 17.5 in HG
I am almost willing to bet those of you seeing say more than 18 have gauges that may be slightly off, less than .5 psi (or 1 in HG)
thoughts?
