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Ash worte this a while back: "The stock turbo Z pushes around 9.5psi. This is accomplished by the ECU through a set of wastegate actuator solenoids. Basically, there is a T-junction in the vacuum line running from the intake piping to the wastegate actuators. This line branching away in the middle actually vents into the atmosphere, except for the electric solenoid valve blocking it off. The ECU reads the actual boost pressure in the intake plenum (there is a line running from the balance tube to a boost pressure sensor behind the driver's front fenderwell) and as it begins to rise into the positive, the ECU begins pulsing a voltage signal to the wastegate actuator solenoids. When energized, the solenoids open and allow some of the boost pressure in the vacuum line running to the wastegate actuators to bleed off into the atmosphere. The rapid on/off pulsing of the solenoids acts as a slow leak so that by the time the pressure on the wastegate actuator diaphragm reaches 7psi, the boost pressure in the intake plenum is actually around 9.5psi. The ECU also takes other sensor signals into consideration, and if it decides that an unsafe condition exists then it will not send any pulses to the wastegate actuator solenoids. When they remain closed, the wastegates will operate at their 7psi mechanical limit...we call it "safety boost." I was unaware this is how the Z's OEM boost control operates. Up to the moment I came accross this statement, I beleived OEM boost control was purely mechanical. Turns out there is an element of EBC in it. When I converted my car to a Blitz EBC, I powered the valve via NC relay with the coil voltage provided by the leads of the right side boost solenoid. I did this to retain the safety boost feature. I had no idea (unil now) that the power to the boost solenoids was pulsed. What this means is that for some period of time (manifold pressure), the brain of my Blitz EBC has intermitent control of its valve. Being that this valve is NO, during this pulsing time, boost level in my engine is at the mercy of the actuator springs.
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