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-   -   Boost Target at higher altitudes? (http://legacygt.com/forums/showthread.php?t=171809)

Jebus 10-07-2011 12:26 PM

Boost Target at higher altitudes?
 
So I live up in Salt Lake City, UT around 4600 ft. I am running Cobb Stage 1 93 Octane on my 2010 GT and I notice that in Live Data under "Boost Target" it's only 15.1psi. Now when I read the map notes it says the boost target is 17.0psi +/- 1psi. Does anyone know if the ECU adjusts the boost target based on barometric pressure? I can't see why it would, since, as far as I understand, the boost target is XX psi ABOVE ambient pressure.

Lardo420 10-07-2011 12:29 PM

correct. Boost pressure is gage pressure, not absolute pressure. If it were absolute pressure and you were running 15.1psi, your pressure would be 29.8psi since atmospheric pressure is 14.7

Types4 10-07-2011 01:02 PM

1 Attachment(s)
Quote:

Originally Posted by Jebus (Post 3582334)
So I live up in Salt Lake City, UT around 4600 ft. I am running Cobb Stage 1 93 Octane on my 2010 GT and I notice that in Live Data under "Boost Target" it's only 15.1psi. Now when I read the map notes it says the boost target is 17.0psi +/- 1psi. Does anyone know if the ECU adjusts the boost target based on barometric pressure? I can't see why it would, since, as far as I understand, the boost target is XX psi ABOVE ambient pressure.

Yes the ecu adjusts boost based on barometric pressure. It will reduce boost by a % value as shown in this table. The top line x axis is the barometric pressure. At 4600ft you are at roughly 12.4psi barometric pressure. So your ecu will begin lowering boost targets from 4000 rpm up.

Jebus 10-07-2011 02:39 PM

Cool, thank you for your help guys, I think I understand this a little better. Does anyone know the reason behind this? Maybe since the ambient air isn't as dense, the turbo would have to work harder and flow a higher CFM of air to achieve the same boost target above atmospheric pressure?

satkye 10-07-2011 02:51 PM

How much boost should you be getting with out mod or access port? Cant seem to find it and i did search forum

Rogue77 10-07-2011 02:52 PM

^^I am not exactly sure on this but I thought it was in the 12 range...

satkye 10-07-2011 03:00 PM

I must be shifting in wrong place when im accelerating it looks like around 10 is th hightest i ever go but i don stay in the log i did of it was very ip and down. Was weird.

SurlyOldManMN 10-07-2011 03:19 PM

Quote:

Originally Posted by Rogue77 (Post 3582607)
^^I am not exactly sure on this but I thought it was in the 12 range...

Gear dependent. 1st and 2nd are lower, I don't recall how much. 12 is what Cobb says on their Stage0.

Types4 10-07-2011 03:28 PM

Quote:

Originally Posted by Jebus (Post 3582586)
Cool, thank you for your help guys, I think I understand this a little better. Does anyone know the reason behind this? Maybe since the ambient air isn't as dense, the turbo would have to work harder and flow a higher CFM of air to achieve the same boost target above atmospheric pressure?

Exactly, the turbo has to work much harder to hit the boost targets and in order to preserve the turbo longevity most cars will kick it back some at altitude.

Jebus 10-07-2011 04:19 PM

Thank you Types4, this has had my mind in knots trying to figure it out. Kind of a bummer that not only does it drop 2psi atmospheric, but another 2psi from the turbo so you lose 4 pounds of absolute pressure. I can't imagine how these cars feel at sea level with 93 Octane.


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