A high-performance muffler assembly for exhaust system of an internal combustion engine. The muffler assembly comprises an elongated casing having an inlet port and an exit port, a first pipe disposed within the casing and having an inlet end in fluid communication with the inlet port and an outlet end selectively fluidly connected to the exit port of the casing, and a first valve mounted within the casing. The first valve is selectively movable between a closed position and an open position for regulating an exhaust gas flow through the first pipe. The muffler assembly is operable in a number of different modes of operation including a high-performance mode, an exhaust braking mode, a reverse-flow mode, etc., determined by the positions of the first valve of the muffler assembly.