Originally Posted by Jebus
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.