Its a 3-port boost control solenoid. It allows for significantly better boost response as well as better overall boost control than can be achieved with the stock solenoid. This is achieved because the 3-port solenoid works in an interrupt configuration instead of a bleeder configuration like the stock solenoid. That means the solenoid actually blocks the boost signal from getting to the wastegate actuator untill the system needs the wastegate open. This keep the wastegate closed longer and allows the turbo to spool faster.

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