Duramex Pre-Turbo Exhaust System
The left side manifold has a severe restriction in the area where the steering shaft passes by. This restriction drops the flow area to approximately 50%. It is believed that this indentation was cast into the manifold in anticipation of installing the Dmax into another chassis (C/K trucks?) and the clearance is quite excessive on the Silverado HD platform.
This is the modified manifold that I used to run on my 2002 Chev several years back. The indented area was cut away, and a patch plate welded in providing a much larger flow area. This manifold served me well, but eventually cracked and was discarded. We now offer the BD replacement manifold which is specially built without the restriction and is a direct bolt in.