A method for automatic, heat release computation in a piston engine, comprises the steps of: measuring a cylinder pressure as a function of crank angle (see FIGURE), based on said measurement; calculating a first polytropic exponent for a compression stroke (in M), based on said measurement, calculating a second polytropic exponent for an expansion stroke (in M′); for a crank angle interval between the compression stroke and the expansion stroke, performing an interpolation of the first and second polytropic exponents and performing a net heat release computation based on said interpolated polytropic exponent.