Help understanding vacuum reading from digital boost gauges...
#1
Help understanding vacuum reading from digital boost gauges...
Fellas, I'm looking for a little help here. I've got a digital boost gauge from SPA and a GReddy Profec B Spec II boost controller. Both of which give me vacuum readings in some sort of negative PSI numeric value, which I don't truly understand and can't convert to inches of vacuum like we do here.
Does anyone know the conversion?
My current vacuum is -60 on the boost controller and the boost gauge. My controller is set to read in PSI, so this would equate to -6.0 PSI of vacuum. I'm just wondering if anyone can give me an idea of what that would equate to?
Thanks guys!
Nick
Does anyone know the conversion?
My current vacuum is -60 on the boost controller and the boost gauge. My controller is set to read in PSI, so this would equate to -6.0 PSI of vacuum. I'm just wondering if anyone can give me an idea of what that would equate to?
Thanks guys!
Nick
#6
I've done a compression test before and know it's good but want to be able to monitor it's health without having to do another compression test.
Nick
EDIT: Now that I think of it, the idle is set that high because my Microtech doesn't have closed loop idle control and as such, it can't fast idle on startup. That's why it is that way, according to the tuner.
Last edited by Brilliant7-LFC; 06-09-17 at 07:57 AM. Reason: I remembered!
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#9
RX-7 Bad Ass
iTrader: (55)
So did some Googling around.
First off, there are WAY more pressure and vacuum units out there than you would think. In the US vacuum is typically measured in inches of mercury (in Hg) - it's literally how many inches the vacuum would pull mercury up a glass tube.
It looks like the Profec doesn't have enough display digits to properly display vacuum, so there's a missing 1 at the front. So -60 is actually 16.0 inches of mercury.
The manual is vague about this. They really only talk about the pressure reading, not the vacuum reading.
When you are in boost, I'm assuming it is displaying in PSI and the display should NOT show the "x100 %kPa" in the corner.
More in the manual -
http://www.greddy.com/upload/file/PRofec_Bspec2.pdf
The fact that the Profec B doesn't have enough display digits and doesn't have a period in the display doesn't make it the best way to show vacuum.
Dale
First off, there are WAY more pressure and vacuum units out there than you would think. In the US vacuum is typically measured in inches of mercury (in Hg) - it's literally how many inches the vacuum would pull mercury up a glass tube.
It looks like the Profec doesn't have enough display digits to properly display vacuum, so there's a missing 1 at the front. So -60 is actually 16.0 inches of mercury.
The manual is vague about this. They really only talk about the pressure reading, not the vacuum reading.
When you are in boost, I'm assuming it is displaying in PSI and the display should NOT show the "x100 %kPa" in the corner.
More in the manual -
http://www.greddy.com/upload/file/PRofec_Bspec2.pdf
The fact that the Profec B doesn't have enough display digits and doesn't have a period in the display doesn't make it the best way to show vacuum.
Dale
#10
Hey Dale thanks for doing that research buddy! I am not 100% sure it's correct though simply because if you're in partial throttle conditions and vacuum, you watch the gauge for example go from -60 at idle to -50 and so on but if a 1 is all that's missing than when it says -10, that's really 11 inches? That doesn't seem right.
Think if it like this: if to go from -60 to -50 is ten places and that takes you from 16 inches to 15 inches. Than how could going from -10 to 0, which is also ten places take you from 11 inches to zero pressure. You get where I'm coming from?
Nick
Think if it like this: if to go from -60 to -50 is ten places and that takes you from 16 inches to 15 inches. Than how could going from -10 to 0, which is also ten places take you from 11 inches to zero pressure. You get where I'm coming from?
Nick
#11
Boilermakers!
iTrader: (157)
PSI is just being display x10, so 14.5PSI show up as 145 and -8.0PSI of vacuum is display as -80, which is -16.2882inHg. Dale is right that it is short of display unit, it is missing everything after a tenth of a decimal. So it can't display -18inHg of vacuum which should be -8.84077PSI, instead you'll see either -8.8PSI/-17.917inHg or -8.9PSI/-18.1206inHg, but I don't think that's a big deal, as long as your positive pressure is being display properly
#12
Original Gangster/Rotary!
iTrader: (213)
There's no reason to be idling at 1250 with a large street port----- You should be able to chill at 950-1000 all day long. Fast idle at cold start isn't needed, my FD sits at 1000ish regardless of water temp, electric load etc. What apex seals are you rocking Niko?
#13
PSI is just being display x10, so 14.5PSI show up as 145 and -8.0PSI of vacuum is display as -80, which is -16.2882inHg. Dale is right that it is short of display unit, it is missing everything after a tenth of a decimal. So it can't display -18inHg of vacuum which should be -8.84077PSI, instead you'll see either -8.8PSI/-17.917inHg or -8.9PSI/-18.1206inHg, but I don't think that's a big deal, as long as your positive pressure is being display properly
Nick
#14
There's no reason to be idling at 1250 with a large street port----- You should be able to chill at 950-1000 all day long. Fast idle at cold start isn't needed, my FD sits at 1000ish regardless of water temp, electric load etc. What apex seals are you rocking Niko?
Nick
#15
RX-7 Bad Ass
iTrader: (55)
Really, I just wouldn't rely on the Profec for a vacuum reading. With the display not having enough room to properly display it and chopping off numbers it's just eye candy as far as vacuum is concerned.
Dale
Dale