Originally Posted by jdpsearcher
But doesn't the wastegate open up completely once target boost is reached no matter what the duty cycle is, thus bleeding off excess boost....
its not a matter of the wg being able to mechanically control it. its that the Target Boost calculation in the ecu changes with atmospheric pressure.
If you take a stock STi that targets 14.7 psi at sea level and drive it to 6000ft the target boost will be 10.7 psi.
This causes a problem when tuning at altitude because you either have to change the target boost to compensate.....IE you would have to target 18.7 psi on that stock STi for it to target 14.7 at 6000ft......or you could try using the atmospheric pressure compensation for the target boost and wgdc and basically guess at how much to increase them.
The best way to deal with cars that are going to be changing altitudes is to get logs from them.
Originally Posted by flycaster
Tim Bailey always told me to not run my highest sea-level boost map when I'm running at home (4K+ elevation) - he had me build a boost map that runs 2 lbs less boost for use at altitude. This was with an AVCR ECBS and EWG.
I'd always thought the issue was the altitude induced change in PR which causes the turbo output to heat up. Am I mistaken?
Yes, you're correct. If you run the same boost at altitude you start running the turbos at higher pressure ratios and lowering the efficiency.
PR = atm press(14.7) + 26psi (boost) / 14.7 = 2.76
PR = (11.7+26) / 11.7 = 3.22