Abstract: An intake conduit or manifold for air for combustion engines has an auxiliary burning chamber provided in one of its walls which communicates with the interior of the intake conduit. A valve can establish or terminate communication between the chamber and the conduit in a sense permitting some of the air from the latter to flow into the former. An injector injects vaporized fuel into the burning chamber and a spark plug ignites the fuel so that the heat of combustion is transmitted to air flowing through the intake manifold to thereby preheat such air.