This paper describes the results of durability tests of monolithic catalytic converters with mechanical devices used to tailor the exhaust gas flow. Deflectors of several different shapes show promise of extending the useful life of the converter by improving conversion efficiencies of hydrocarbons and CO. The tests were run on engine/dynamometers with round cross-sectional area samples and with symmetrical inlet cones. Improvements are found in initial activity and reduced deterioration. The penalty for altering the flow is in slower catalyst light-off and increased pressure drop.Sequential photographs of catalyst light-off with different flow distributions are included as well as postmortem analysis of catalyst loading and poison deposition.The potential benefits appear to be a result of a more balanced exhaust gas flow over the monolith cross section and thereby providing more effective use of the catalyst.