Marc is correct as always, BUT for a general idea I have been told that the WASTEGATE (oem) that is . opens at 1/2 of what would be considered as your peak Boost allowed, or obtainable. ex. OEM Boost peak 24-25 PSI, meaning that the OEM wastegate STARTS to open in this ex at 12-13 PSI.
It continues to open progressively more and more as boost level peaks.
This is not a specific example that can be applied to all wastegate operations, but how the wastegate functions in the specific enviroment used in this example. I don't mean to be confusing, maybe this example helps a little. If I can stand corrected please may others correct or clarify my post. This is how it has been explained to me. GOOD LUCK