If I understand it correctly, and from looking at the vacuum tube routing on the stock turbo compared to the GM setup... This allows you prevent boost pressure from reaching the wastegate actuator until a certain point. Would it even be possible to keep the wastegate shut all the time? In the stock setup, the wastegate actuator is connected directly to the turbo output via vacuum tubing. With the GM BCS, the two are connected through the solenoid, so the solenoid can keep pressure from the wastegate actuator.