Turbo Anti Lag
As found on WRC rally cars, turbo anti-
Boost pressure is regulated by the turbo wastegate which is opened at a boost pressure set by the actuator. To increase boost pressure at which the the wastegate is opened, the actuator needs to see a lower pressure than actually exists in the inlet manifold. The ECU can control a solenoid or air injector to do this. The solenoid or air injector can be turned off / on to give low (actuator level) and high (ECU controlled) boost.