This paper describes a computational study of a full size catalytic converter. The simulations are validated against experimental data obtained from the literature. It is seen that the flow distribution under both reacting and non-reacting conditions is a strong function of the converter properties, including such factors as the monolith cell density, the diffuser angle and the aspect ratio. The mass flow rate of the feed also has a strong influence. Monolith substrates with a high cell density showed faster light-off for a model reaction. A dual zone monolith consisting of a high cell density core and a low cell density outer annulus showed worse performance in the light-off compared to all other configurations tested. The overall execution time required for a two dimensional simulation required anything from under a minute for a steady state cold flow test, to 2 h for a transient light-off with reaction. (C) 2012 Elsevier B.V. All rights reserved.