A receptacle type intermediate connector 1 has an insulated body 2 with a forward end opening 3 for reception of a mating connector, and contacts 4 fixed in the body and each having at its end a finger 5 for engaging a foreign contact held in the mating connector. The lift includes a base and a mast extending therefrom. Incorporated within the changeover portion is a heat treatment chamber through which a stream of hot gasses can be passed. Near the end of the compression stroke, the cylinder head recuperator is moved back into the recess so that compressed charge located in the recess is forced to flow through the hot cylinder head recuperator and thereby be heated up immediately before ignition of the compressed charge.