Abstract: A dual wall, air gap exhaust manifold with an integral inlet connecting flange defining an elongated, internal, air injection passageway enclosed by an L-shaped plate welded over an elongated slot in the flange to form the elongated passageway, the L-shaped plate also being welded over a series of short channels which extend between the elongated passageway and the manifold inlet openings. The elongated passageway has an air inlet connector. The spaced dual walls of the manifold runners are joined together at the flange openings, just downstream of the channels.

Abstract: An acoustically improved, air gap engine exhaust conduit having a dual wall, air gap, metal exhaust conduit of an outer jacket and a thin inner liner, the jacket having at least one exhaust gas inlet and an exhaust gas outlet, the liner having at least one inlet and an outlet, the jacket inlet and the liner inlet being adjacent each other, the liner being secured to the jacket adjacent the jacket inlet and the liner inlet, the liner outlet being optionally in engagement with the jacket, and the liner otherwise being spaced from the jacket over its length to form a continuous air gap from the liner inlet to the liner outlet, a pattern of indentation ribs protruding into or out of the jacket over substantially all of said jacket, each indentation rib protruding toward or away from the liner, and terminating short of the liner to be spaced from and not in engagement with the liner, to maintain the continuous air gap.