An exhaust manifold and related method have a hybrid clamshell construction including an outer manifold half stamped from a first metal and having a first wall thickness, as well as an inner manifold half stamped from a second metal that is different from the first metal and has a second wall thickness which is different from the first wall thickness. Opposite side edges of the outer and inner manifold halves are rigidly interconnected to define a hollow manifold bottom. Port and outlet flanges are rigidly attached to inlet and outlet sides of the manifold body.