Indicated Mean Effective Pressure models (IMEP) are essential to estimate the indicated torque in internal combustion engine; they also provide important information about the mechanical efficiency of the engine thermodynamic cycle which describes the conversion of the fuel combustion energy into mechanical work. In the past, many researches were made to improve the IMEP prediction and measurement techniques at different engine operating conditions. In this paper, we proposed a detailed IMEP model which separately describes the IMEP-Low pressure and the IMEP-High pressure of a modern diesel engine; the IMEP is the direct subtraction result between these two variables. We firstly studied the evolution of the IMEPHP and IMEPLP with respect to the engine's variables and then we deduced the variables of influence and the form of the equations that can be used to develop the models. Finally, the models' coefficients were determined based on experimental data collected on a steady state test bench and using the least square regression method. In addition, the IMEPHP model results were compared to transient experimental data collected on a chassis dynamometer test bench; the model results are in excellent agreement with the experimental data. (C) 2011 Elsevier Ltd. All rights reserved.