Catalytic converters are a primary component of an automotive emissions control system used to control exhaust emissions to the low levels required by current regulations. During cold starts, the converter is ineffective until it reaches a lightoff temperature of approximately 3500 C. During this time 50% to 80% of the regulated hydrocarbon and carbon monoxide emissions are emitted from the tailpipe. To reduce these cold start emissions to meet the more stringent emission standards required by the Revised Clean Air Act of 1990 and the more restrictive California emissions standards, the catalytic converter must be heated quickly to lightoff temperature.Conservation of exhaust thermal energy is one of several approaches being studied to quicken lightoff. Much thermal energy is available in the gases leaving the combustion chamber with temperatures exceeding 350°C following engine ignition. However, cold engine parts, cold manifolds and cold exhaust pipes cool these gases before they reach the catalytic converter. Analytical models were used to investigate the impact of exhaust system changes on converter inlet temperature and its impact on converter lightoff and cold start emissions. The models allow evaluation of converter location and pre-converter hardware design to identify system requirements, with reduced experimental development.