Abstract: A recuperating four-stroke internal combustion engine obtains improves Carnot efficiency by use of a new and novel cylinder head which captures thermal energy normally thrown away in the exhaust and re-introduces it to the working cycle. This result, long sought by others, has been achieved by incorporating within the head a compact internal recuperative heat exchanger in series with a combustion chamber or pre-chamber. A recuperator-protecting valve segregates the recuperator from hot combustion gases until the gases reach maximum expansion in the cylinder. Recuperators of both common-duct and seperated-duct design are described, the separated duct recuperator permitting higher recuperator temperature and increased efficiency and a reduction in the number of valves necessary to control gas flow. A preferred embodiment employs four valves per cylinder unit, a separated duct recuperator, and an insulating liner that surrounds both the combustion chamber and the recuperator.