Abstract: The improved high performance muffler is used to attenuate the sound waves in exhaust gases from internal combustion engines and the like and has a casing, which includes a closed volume defined by side walls, a top wall, a bottom wall and inlet and outlet end caps. The casing also has a defined exhaust gas-flow passageway, which extends between the end caps, which is bounded by upper and lower walls within the casing and the side walls, and which includes inlet and outlet chambers adjacent to the inlet and outlet end caps, respectively. Two spaced apart, gas-flow channels. A gas-flow director assembly, disposed between the side walls and the upper and lower walls, defines two spaced apart gas-flow channels. The gas-flow channels have a uniform, smooth cross-section, and their lengths are substantially equal.