Multi-channel relations between relative combustion chamber diameter (dc.ch/D) and open type combustion chamber diesel engine parameters are analysed. Special attention is paid to optimising diesel engine design in case of wide combustion chamber to get highest efficiency. It is shown that choice of fuel injection equipment may play important part to solve the problem. Results of experimental investigations of cylinder head thermal loading in case of different dc.ch/D values are presented. Attept is made to establish reasons for thermal loading decrease with greater dc.ch/D on the basis of charge velocity components measurements. As it turned out impossible to relate specific heat flux and temperature fields to charge motion alone, assumptions are outlined with regards to corresponding governing factor.In conclusion some of advantages of shallow type combustion chambers as applied to highly boosted diesel engines are stressed along with problems to be solved.