An intake and exhaust system for an internal combustion engine of the type having an auxiliary combustion chamber associated with each main combustion chamber, and wherein the overall air-fuel charge to all combustion chambers is leaner than the stoichiometric ratio, so that excess air is present in the exhaust gases. The system includes integrated intake manifolds, one for connection with the main combustion chamber and the other for connection with the auxiliary combustion chamber, and an exhaust manifold for connection with the main combustion chambers. The exhaust manifold includes a stainless steel liner enveloped within and spaced from a metal casting in order to retain the heat of the exhaust gases so that the exhaust gas temperature remains at or above the temperature at which the unburned hydrocarbons in the exhaust gases will continue to burn. This temperature also promotes oxidation of carbon monoxide to carbon dioxide. The intake manifold is in thermal association with the exhaust manifold to provide a transfer of heat from the exhaust manifold to the intake manifold so that a rich mixture for the auxiliary combustion chambers and a lean mixture for the main combustion chambers are both heated in a controlled ratio. An integral heat riser member is positioned between the exhaust manifold and the intake manifold for transferring heat therebetween. The liner has a collection chamber with a baffle located therein to direct the flow of exhaust gases to insure proper heat transfer to the riser member. Another main feature of the system is to present a minimum heat capacity in association with the exhausting gases to allow the overall system to quickly achieve preferred operating conditions.