A system to cool exhaust gas entering a catalytic converter in a turbocharged engine is disclosed. An air bypass valve is controlled to vent pressurized air to the atmosphere to overrev a turbocharger when exhaust gas exceeds a predetermined temperature. The rotation of the turbocharger increases to maintain a desired boost pressure. When this occurs, the turbocharger absorbs more energy from the exhaust gas to maintain the desired boost pressure. Thus, the exhaust gas entering the catalytic converter is cooled.