Originally Posted by pmckechnie

I'll try to explain how my boost control works. With vacuum to the wastgate all the time can let boost go to 20+ psi (That is as high as my gauge will go.) So to control the boost, I use the flapper valve in the intake crossover to restrict the airflow some. It is adjusted so that when the boost gets to 15 psi in the intake manifold it will close off a little. This only restricts enough to drop the boost to the intake manifold. It never restricts enough to cause a vacuum in the intake, just reduce the boost. It has been this way for several years now with no ill effect. In normal driving the boost seldom goes over 10psi. At WOT it will go to 15 psi until you let off some. So the wastegate is just a safety device that keeps the boost at a safe level. The pressure type wastegate lets some of the exhaust bypass the exhaust turbine in the turbo to reduce boost. The other overboost system blocks boost from getting to the ALDA. This cuts down on the amount of fuel the engine gets. Less fuel = less exhaust = less boost from the turbo. There is always more than one way to skin a cat.

Paul