Modelling of cold-start engine behaviour is a difficult task, in particular the quenching effect of the cold walls on the unburnt and partially burnt hydrocarbons. This paper presents the modelling of cold-start engine exhaust heat transfer which makes provision for predicting the effect of the temperature of the exhaust gas on the conversion of the emissions at the catalysts. The model includes two distinct parts, namely the normal exhaust system and a three-way catalytic converter. The latter is modelled by neglecting the effect of chemical reactions on the gas temperature before the catalysts lightoff. The major emphasis of this paper is on the effect of high values of ignition retard in the engine on the increased enthalpy/temperature of the exhaust gas and, thus, improved catalysts lightoff during cold start.