For meeting upcoming BS IV & BS V emission norms in Heavy Commercial Vehicles, most of the manufacturers are taking SCR after treatment route. Though SCR system is more complex and involves higher cost impact, an optimized SCR system can bring down the payback period to about one year due to improved fuel economy. For development of an SCR after treatment system, selection of a correct SCR catalyst and its position in the system is very important. NOX conversion efficiency of catalyst depends on exhaust gas temperature at the catalyst and the velocity distribution over the face of the catalyst. Generally catalysts are evaluated for the conversion efficiency in engine test bed. In a drive to have a first-time-right solution, a CFD analysis was carried out considering the low and high flow rate conditions. CFD simulation models and the corresponding results were used as a predictive tool in the exhaust system development process. These simulations helped to evaluate design proposals before finalizing the design. Prototype exhaust system components were developed for the best design proposal considering exhaust gas temperature profile, velocity distribution, pressure drop, and conversion efficiency of coated and extruded catalysts. This approach significantly reduced the prototype development and evaluation time.