My personal hypothesis is that the majority of "shifting the curve to the right" is a product of an aftermarket IC, more so than the aftermarket charge tubes:
The reason I say this is because there is a known pressure drop across the OEM IC of 1-2PSI. Therefore the OEM turbo has to push 1-2 PSI more to achieve the actual commanded boost. Which at altitude really becomes crucial, but has an effect at all altitudes because the turbo effectively hits the end of the efficiency curve at a lower engine RPM: because the turbo is having to spin faster than it would have to, if not for the pressure drop across the IC.
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