A widely used acoustic muffler design for motor vehicle exhaust gas systems has a retroverted gas flow path in which gas flows to the downstream end of the muffler, reverses itself to flow to the upsteam end of the muffler, and reverses itself again to flow back to the downstream end and out of the muffler. In some of the mufflers of this type means are provided to guide and direct the flow reversal at the downstream and/or upstream end of the muffler. Curved surfaces formed in one or both of the end headers of the muffler have been used, for example, to provide such means as shown in U.S. Pat. No. 4,381,045, issued Apr. 26, 1983. Turn-around cups mounted on internal partitions to connect the outlet end of one gas conduit to the inlet end of another have also been used to provide such means as shown in U.S. Pat. Nos. 2,182,945 issued Dec. 12, 1939, and 2,934,161, issued Apr. 26, 1960.