The stock exhaust system is less than optimal for a boosted motor. Turbos like no post turbo backpressure, and plenty of flow.

To assist the modified exhaust manifold and the modified turbine housing [covered in the 'miscellany' gallery] operate optimally, and do what I wanted them to do, I knew that the stock exhaust system would have to uprated. The system that was in the wagon was not in terrible condition; it would have lasted a while yet. But, the flow capabilities was insufficient for my purposes.