View Full Version : Boost pressure at altitude
S4MAXSPEED
04-15-2015, 06:43 PM
So in preparation for going EPL Stage II, I installed an AWE boost gauge over the weekend. Great gauge and fairly easy install(maybe).
Question: Max boost that I'm seeing is only 8 psi on the gauge. I know that the bypass valve will stay closed to keep boost pressure up here in the Denver area, but does that also mean we never get to the full boost of 11-12 psi on stock software.
Other possibility is the way AWE has the boost line run to the sender is through the dash where the ECU slides in. It's a tight fit and I may be pinching the line. Before I do more surgery though I wanted to see others opinions on the matter.
Sounds about right that your peak boost is going to be 2-3 psi less absolute pressure than the guys at sea level. The difference is stock ECU wants to taper to 7-8 psi as you get in the upper RPMs - so bypass opens and boost is lost for the guys at sea level - but yours should mostly hold (bypass stays closed)
jimrobbington
04-15-2015, 07:14 PM
Is it a digital or analog gauge? If it's analog, or will need to be adjusted for our elevation. Does it rest at 0 with the power on, but engine off?
jimrobbington
04-15-2015, 07:15 PM
Fwiw, I have a Podi analog gauge, and I needed to set the adjustment screw to correct it for high elevation.
S4MAXSPEED
04-15-2015, 07:32 PM
Is it a digital or analog gauge? If it's analog, or will need to be adjusted for our elevation. Does it rest at 0 with the power on, but engine off?
AWE lists it as an electrical boost gauge. It's an analog readout, but uses a digital sender. I haven't tried to see what it sits at when the engine is off.
There aren't any adjustment screws that I could see on the gauge. Just electrical plugs to plug in from the sender.
As AZT mentioned above, it holds steady at 8 psi all the way to redline. That's why I'm assuming the engine cannot ever make its "full" boost here at altitude.
It's not a big deal really, as it's all relative to the cars around it operating in the same environment.
jimrobbington
04-15-2015, 07:40 PM
AWE lists it as an electrical boost gauge. It's an analog readout, but uses a digital sender. I haven't tried to see what it sits at when the engine is off.
There aren't any adjustment screws that I could see on the gauge. Just electrical plugs to plug in from the sender.
As AZT mentioned above, it holds steady at 8 psi all the way to redline. That's why I'm assuming the engine cannot ever make its "full" boost here at altitude.
It's not a big deal really, as it's all relative to the cars around it operating in the same environment.
Yeah, mine want an obvious adjustment either. It took me quite a while to figure it out. Had to contact the vendor, and the gauge had to be disassembled for me to adjust it. You should not really be getting less boost at altitude, just less power, unless SC is that much different than turbo. I still push 20-24 psi on my little K03 better than many at sea level.
jimrobbington is correct that you aren't getting less boost - you are boosting 10-11 psi above the outside air that is -2 or -3 psi (as compared to sea level) which causes the gauge to read 8 psi :) Zero-ing out or adjusting the gauge for your ambient pressure would make it read ~11psi to redline.
You are not generating less boost.
If you do not zero the gauge then the needle will show a negative offset. If it shows a -5mmHg vacuum reading with the engine off, then that is an approx. -3psi offset for the boost reading.
So if you were expecting see 11psi then it will show a reading of 8psi instead.
I hope that makes sense.
jimrobbington
04-16-2015, 04:38 PM
You are not generating less boost.
If you do not zero the gauge then the needle will show a negative offset. If it shows a -5mmHg vacuum reading with the engine off, then that is an approx. -3psi offset for the boost reading.
So if you were expecting see 11psi then it will show a reading of 8psi instead.
I hope that makes sense.
Winston! Just the man who told me what was going on like 6 years ago when I had this issue. Good man!
It's been 6 years already! [eek]
jimrobbington
04-16-2015, 04:44 PM
It's been 6 years already! [eek]
Something like that. Finally trying to sell my B7 A4 and get a B8 S4.