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Does anyone know what the boost gauge actually displays, or how it calculates what to display?

I ask because I had an issue yesterday where the cold air intake got severely restricted (very dumb mistake on my part) and the car basically ran out of breath at about 2500 RPM in second gear and just could not rev any harder - same thing essentially in third.

What was weird was that until I worked out that something was wrong, the car would be going nowhere but the boost gauge was showing 50% of scale in second and about 75% in third (its a 2017). I fixed the restriction and everything went back to normal.

So I was thinking if the intake was pretty much restricted then the car could not have actually been making that much boost - so what was the gauge actually showing?
 

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Does anyone know what the boost gauge actually displays, or how it calculates what to display?

I ask because I had an issue yesterday where the cold air intake got severely restricted (very dumb mistake on my part) and the car basically ran out of breath at about 2500 RPM in second gear and just could not rev any harder - same thing essentially in third.

What was weird was that until I worked out that something was wrong, the car would be going nowhere but the boost gauge was showing 50% of scale in second and about 75% in third (its a 2017). I fixed the restriction and everything went back to normal.

So I was thinking if the intake was pretty much restricted then the car could not have actually been making that much boost - so what was the gauge actually showing?

If i recall correctly, the factory boost gauge just moves by whim of the ecu, it is not actually displaying boost accurately.

So you are not crazy. The gauge is a "dummy gauge" like the oil temp.

The ecu can read real boost and show it via an external viewing device, like an Accessport. The gauge on the dash is just flair.
 

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If i recall correctly, the factory boost gauge just moves by whim of the ecu, it is not actually displaying boost accurately.

So you are not crazy. The gauge is a "dummy gauge" like the oil temp.

The ecu can read real boost and show it via an external viewing device, like an Accessport. The gauge on the dash is just flair.
While Duece is correct, it's been proven to be extremely accurate in the past. Apparently you just found a way to trick the ecu...by suffocating it lol. Interesting.
 

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If i recall correctly, the factory boost gauge just moves by whim of the ecu, it is not actually displaying boost accurately.

So you are not crazy. The gauge is a "dummy gauge" like the oil temp.

The ecu can read real boost and show it via an external viewing device, like an Accessport. The gauge on the dash is just flair.
Actually the gauges in the pod are fairly accurate. I compared them to my Defi gauges. Not just for flair. They get the same readings the access port does.

Sent from another garage.
 

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Actually the gauges in the pod are fairly accurate. I compared them to my Defi gauges. Not just for flair. They get the same readings the access port does.

Sent from another garage.
This i find hard to believe. I always see that gauge move load dependant. Not boost level. I will do some highway pulls and further investigate.

The oil temp is just using math from the ecu, there is no oil temp sensor.

Im not sure about the oil pressure.

I just use my AP3 for gauges anyway.
 

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This i find hard to believe. I always see that gauge move load dependant. Not boost level. I will do some highway pulls and further investigate.

The oil temp is just using math from the ecu, there is no oil temp sensor.

Im not sure about the oil pressure.

I just use my AP3 for gauges anyway.
The AP3 gets its info from the computer just like the gauges done. However instead of an analog readout it's digital.

Sent from another garage.
 

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On a related note, is the boost gauge linear? Meaning the middle hash mark is 15psi because bottom end is 0 and top end is 30
 

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Top end is 25. Pretty sure it is.

Sent from another garage.
My 2017 says 30. Regardless, is the middle hash half of whatever the top end number is? Or is it scaled weird?
 

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On a related note, is the boost gauge linear? Meaning the middle hash mark is 15psi because bottom end is 0 and top end is 30
Top end is 25. Pretty sure it is.

Sent from another garage.
Varies by year. 2013-14 ST's have a max of 25. 2015-17 have a max of 30.

So if you have a 13/14 then the lines are 6.25, 12.5 (half), 18.75, 25.
If you have a 15/16 then the lines are 7.5, 15 (half), 22.5, 30.
 

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Didn't realized that small change.

Sent from another garage.
First time I got into a 15 I was immediately like wow we got cheated lol. We are a BT upgrade away from a near useless boost gauge in the 13/14.
 

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First time I got into a 15 I was immediately like wow we got cheated lol. We are a BT upgrade away from a near useless boost gauge in the 13/14.
Yep. Mine just pegs at 25 when I'm over 25.
 
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I really really wanted to post "boost" as my answer..LOL

good info though, I knew it wasnt an actual boost reference, but I thought for sure the ECU was taking an accurate manifold pressure and outputting an accurate depiction of that.
 

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It comes from the sensor on the hot side of the intercooler. I think it is MAP not MAF but I could be wrong.
 

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The AP3 gets its info from the computer just like the gauges done. However instead of an analog readout it's digital.

Sent from another garage.
You sir are quite correct.

Well i actually compared it to the AP3 some on the way home today. It does seem to respond well to boost, but it is a total pain in the ass to try and read. It has like no real reference marks. 25 is a red zone, then the rest is just 4 hashes.

Trying to read it in my paint shaker of a car is practically impossible.

I was half tempted to stick my AP3 to my touch screen, and set up my camera to record both for comparison. That would yeild better results, but then again, nothing is steady in my car. Rattle rattle.

So it seems accurate, but the gauge itself sucks balls to use.
 
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