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. Optionally, the liner can have a pattern of indentation ribs protruding inwardly or outwardly and, if the latter, terminating short of the jacket so as not to engage the jacket and leave an air gap over the length thereof.