A combined one-dimensional, multi-dimensional computational fluid dynamic modelling technique has been developed for analysis of unsteady gas dynamic flow through automotive mufflers. The technique facilitates assessment of complex designs in terms of back-pressure and noise attenuation. The methodology has been validated on a number of common exhaust muffler arrangements over a wide range of test conditions.Comparison between measured and simulated data has been conducted on a Single-Pulse (SP) rig for detailed unsteady gas dynamic analysis and a Rotary-Valve (RV) rig in conjunction with an anechoic chamber for noise attenuation analysis. Results obtained on both experimental arrangements exhibit excellent gas dynamic and acoustic correlation. The technique should allow optimisation of a wide variety of potential muffler designs prior to prototype manufacture.