Based on the wiring schematic that I have it says that the overboost is supposed to take it out at around 15.9 psi. I drove a car recently with the wastegate line disconnected and it would get up to 16 psi. I never kept my foot in it to see how much higher it would go which to reinforce what eskimo is saying. I will mention that I was scared to keep my foot in it so I never really gave it much chance to go any higher.

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Jim