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This work analysis the causes and presents solutions for the non-uniform distribution of the flow in an automotive catalytic. The catalytic converters are usually installed in the exhaust pipe of the vehicle, with a diffuser connect ivy housing of the monolithic ceramic. The diffusers currently used do not provide a good performance, because of their high area ratio (A > 3) and large divergence angle (2θ > 10°). Due to boundary layer separation on the walls of the diffuser, the flow occurs in the form of a “jet”, with high speeds at the center. The non-uniform distribution of the flow causes an irregular use of the catalytic area. The results are an increase in the production costs, in the pressure drop and in the time to “light-off”. In this work, the non-uniformity of the flow was measured with a Pitot tube, in an experimental rig specially designed for this purpose.