The outside wastegate plumbing is more complicated.

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External Method of Wastegate:

This is known as the “tee” method, as there has to be a tee connected to the boost pressure source in order to ensure that boost pressure is always delivered to the lower part of the wastegate. The way this system works is very simple once you look at it from a different angle although it might seem unclear at first glance.

• The wastegate’s bottom ALWAYS is flooded with a boost. When the pressure of boost is greater than the pressure of the wastegate spring gates valves will open to open and decrease the boost.
• The solenoid for boost control’s “NC” port always sees the boost pressure. Its “C” port of the solenoid is connected directly to the upper port in the Wastegate. Since it’s “Normally Closed” nothing happens unless the boost solenoid has been activated.
• Once the boost solenoid has been activated, surge pressure will be applied through the solenoid to on top of the wastegate. This pressure is offset by pressure being transferred to the bottom port, leading to the reduction of differential pressure over the diaphragm. (The diaphragm is now trying to shut the valve from above which is counteracting the force that opens it that is coming through the lower port.) This results in increased pressure at the upper outlet, which results in an increased boost.
• I.E. If there is a 14psi spring inside the wastegate, it is normal that 14psi could break open the gate. If you add 2psi to the high point of your wastegate you will require 16psi down the middle to break the wastegate.
• The solenoid can operate at 100% efficiency, resulting in no differential pressure. The wastegate will function the same as if there were hoses connecting it either at its top or bottom, in that the upper and lower wastegates will be experiencing exactly the same amount of pressure.

The Tee method is the best method for plumbing outside wastegates. Although I haven’t tried testing the response and properties for the different boost control methods back on the same set-up, however, it’s something I’ll need to test to determine the differences in the event that there are any. Based on my experience, the basic method works well in the majority of scenarios and could be the preferred choice if you are looking for simplicity.