The spatial variation of instantaneous heat transfer in a highly rated DI diesel engine (130 mm bore, 150 mm stroke) has been investigated. Measurements have been made at key locations within the combustion chamber (valve bridge, above the piston bowl lip and bore edge) at test conditions covering the engine speed and load range. Total and radiative heat flux probes have been designed and developed to enable both the convective and radiative heat transfer components to be quantified. Transient calibration techniques have also been developed to establish the dynamic characteristics of the heat flux probes. This has removed the uncertainty normally associated with surface thermocouple diffusivity values. Considerable spatial variations in both peak and mean heat transfer have been found. The measured spatial and temporal variation in heat flux have been compared with established heat transfer models. An additional study has also been carried out to compare instantaneous heat transfer from the normally cooled and a re-optimised thermally insulated version of the test engine. Both mean and peak instantaneous heat transfer were reduced in the insulated engine by an amount consistent with the increase in wall temperature.