The technique of using cylinder pressure data for diagnosing the combustion process in a reciprocating internal combustion engine has been used for some time. Much of the early work, however, was qualitative comparisons of the heat release rate diagrams. Only recently have efforts been made to reduce the heat release diagrams to functional or numerical representations which could be used to make fuel-to-fuel and engine-to-engine comparisons.This paper describes work in which cylinder pressure measurements were taken from an operating diesel engine using a high-speed data acquisition system. Combustion chamber pressure measurements were made at approximately 1.0- degree increments over several engine cycles using a real-time data acquisition system.The pressure data were used to calculate apparent heat release and indicated horsepower. Both radiative and convective heat transfer computations were included in the calculational procedures. The equipment and techniques used in obtaining the pressure measurements are discussed, and the computer programs used to obtain and analyze the data are described. The heat transfer analysis is presented, and several parameters are defined for quantifying the heat release curves. Regression analysis was used to examine the effect of the defined heat release parameters on the indicated horsepower.