A change in essential operating parameters of a high speed direct injection turbocharged diesel engine MAN D0826 LOH15 during the injected fuel mass flow variation was presented. Based on two measurement sets, performed with standard diesel fuel, several operating parameters were calculated: engine torque, effective power, excess air ratio, specific effective fuel consumption and heat released per engine process. All of the calculated parameters are presented for a wide engine operating range. Along with calculated, several important parameters were measured, in addition to those presented in measurement sets. Additional measured parameters were lubrication oil temperature and exhaust gas temperature before and after the turbocharger turbine. Those calculated and measured parameters allow deep insight not just into the engine process, but also in the process of turbocharging, which is very important in the analyzed diesel engine operation.