The downsizing of Internal Combustion Engines (ICE) is already recognized as a very suitable method for the concurrent enhancement of Indicated Fuel Conversion Efficiency (IFCE) and the lowering of CO2 and NOx emissions. In this report, ultra-downsizing is introduced as an even higher stage of development of ICE. Ultra-downsizing will be implemented here by means of real Atkinson cycles using asymmetrical crank mechanisms, combined with multi-stage high-pressure turbocharging and very intensive intercooling. This will allow an increase of internal combustion engines (ICE) performance while keeping the thermal and mechanical strain strength of engine components within the current usual limits.