Three dimensional simulations of the non reacting flow field within two different designs of close coupled catalytic converters have been performed. Close coupled catalytic converters are, by design, mounted very close to the engine exhaust manifold and the two components selected for this work are typical of the two approaches to manifold design namely cast and pressed. Block structured grids were developed from a combination of CAD data and paper drawings using both I-DEAS™ and PATRAN™ geometry modelling and meshing software. The flow-field was then calculated using the STAR-CD™ Finite Volume Computational Fluid Dynamics (CFD) software using an HP-720 workstation. Using the results of the CFD calculations the two exhaust designs were compared by calculating maldistribution indices of the velocity distribution within the monolith region. The results show that the component with the pressed manifold has on average a 28% lower maldistribution index than the component with the cast manifold.