A new method to obtain a complete performance map of I.C. Engine based on limited experimental data is proposed. It employs extrapolation of regulator characteristics of break specific fuel consumption (BSFC) data to cover the whole field of multi-parameter performance map of the engine. The method is based on the mathematical correlation (of the second-order polynomial type) between BSFC and engine speed and torque. This correlation might be obtained with the help of special computer program. Once established for an engine, this polynomial provides calculation of appropriate equations for the lines of constant BSFC on the performance map of engine. The complete engine performance map can be obtained through computer treatment of available standard total and partial regulator characteristics of the engine without carrying out any special experiments.