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Discussion Starter · #1 ·
Hey folks,

For those of you with aftermarket boost/vacuum gauges and increased boost, can you post your vacuum reading at idle?

I'm only seeing 16"Hg at idle (running a 2.93" upper and 2lb lower) and I think that it's low. IIRC, it has dropped about 2"Hg with the addition of the 2lb lower and 3rd idler. I'm thinking that I either have a vacuum leak or the increase blower speed at idle is too much for the bypass (or the bypass isn't adjusted properly).

Thanks,

MJ
 

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Discussion Starter · #2 · (Edited)
Well, found the culprit. The Autometer Lunar boost/vacuum gauge is off. A buddy just came over and brought with him a precision vacuum gauge and it read 20-21"Hg at idle where as the Lunar gauge only read 16"Hg. Makes me wonder just how accurate it is under boost. :(

Also, just tested the boost gauge and found out that I had an air leak up at the compression fitting on the back of the gauge. It would bleed off vacuum when tested with a MightVac. I tightened the fitting and the leak went away. This maybe why my *reported* peak boost has dropped 1-1.5psi over the past week or so.

MJ
 

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The Ubiquitous Jimmy V.
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Mine with 3in pulley only gets 18 vacuum on start up ,,Then 20 to 21 when warmed up..

jim v.
 

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Discussion Starter · #4 ·
Jim Vaccaro said:
Mine with 3in pulley only gets 18 vacuum on start up ,,Then 20 to 21 when warmed up..

jim v.
Thank you sir.

MJ
 

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Discussion Starter · #7 ·
AmazonRacing said:
I'm reading 20-21 "hg at idle with a 2.75 upper.

Rick
Cool thanks guys. Glad it was only the gauge being off. I was starting to worry a little.

MJ
 

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vacuum

Mine idles @ 21" hot or cold. Joe
 

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I never checked my vacuum until this thread. When I installed the overlay, I calibrated my gauge to another boost gauge and everything looked good. I just checked the vacuum and it is around 20.5 to 21, so I checked the stock gauge and I did have a vacuum leak at the fitting also. I tightened it up, but now my needle comes down further to the vacuum side? I recalibrated the stock gauge to my precision gauge, but the stock gauge is still where it needs to be, but dang the vacuum sure pulls that needle back now, so what do you all recommend?
 

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Discussion Starter · #11 ·
MineralGray03 said:
I never checked my vacuum until this thread. I calibrated my guage to another boost guage, but the needle pulley to the vacuum side further, then I just checked the vacuum and it is around 20.5 to 21. I checked the stock gauge and hat a vacuum leak at the fitting also. I tightened it up, but now my needle comes down further to the vacuum side? I calibrated the gauge and the stock gague is still where it needs to be, but dang the vacuum sure pulls that needle back, so what do you all recommend?
What do you mean "calibrated" the gauge? Is there a way to adjust the aftermarket gauges?

MJ
 

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mjchip

What I mean by calibrate is adjust the needle to what the precision guage is set at.
For example; if the precision gauge says it is at 10lbs then the stock gauge needle is taken off and put to that postions while vacuum is on the gauge.
This is what Bill Hilton who made the overlays for our stock gauges recommended to do in his instructions, and I have to say it makes a difference.
I am just concerned now that mine is a little off now. I might have to reset or recalibrate the needle.
 
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