The 6.2L diesel has 2 exhaust manifolds made of nodular cast iron, Figure 2-32. Exhaust gases are forced out when a lobe on the camshaft causes the exhaust valve to open and the piston forces the exhaust gases through this opening to the exhaust manifold. Using dual exhaust improves efficiency of the engine by allowing freer exhaust of gases, thus leaving less burned gases for the cylinder at the beginning of the intake stroke.
The mounting flanges are machined to seal the exhaust ports to the cylinder head. It is extremely important that these surfaces be flat, since no gasket is used.