A computer simulation was employed to perform parametric studies on muffler design. Engine exhaust system parameters such as muffler diameter, source-muffler pipe length, number of mufflers, series and parallel installation of mufflers, and the source and termination impedances were considered during the studies. The muffler insertion loss and radiated sound pressure level were predicted for several values of each parameter. An acoustic model consisting of a lumped source-muffler-termination system was used. A scheme was developed using the pressure source model to predict the radiated sound pressure and a simplified expression for the predicted quantity was obtained as a sum of the measured, plane wave and monopole terms. The relationship between the insertion loss and radiated sound pressure level was established for a given set of conditions. A vacuum pump was used as the sound source. An expansion chamber was used as a muffler.