Originally Posted by Brian Carlton

Correct, the overboost is strictly for protection if the wastegate were to stick closed. In reality, I'd venture to say that most of the systems won't work properly due to the sensor on the manifold getting plugged with carbon over time. I recently tested the SD without a wastegate hose. The circuit never worked.

The "banjo fitting" which you've probably heard of, is attached to the back of the intake manifold. It sends a pressure signal to the "ALDA" which allows the IP to advance the rack and provide more fuel to the cylinders.

The wastegate setpoint is a crude spring affair that is not calibrated very accurately on most vehicles. Some are set to 6-7 psi and some are close to the specification of 12-13 psi.