Recent advancements in the combustion control of new generation engines may soon require real time, precise sensing of the cylinder pressure profile to facilitate successful combustion feedback. Currently, even laboratory-grade pressure sensors can deliver pressure traces with insufficient signal to noise quality due to electrical or combustion-induced signal interference. Consequently, for example, calculation of compression and expansion polytropic constants may require statistical averaging over several cycles to deliver required information. This lag in the resultant feedback may be excessive when the calculated combustion metric is used for feedback control, especially in the case of any transients. The method described in this paper involves a special pressure trace filter offering excellent performance which facilitates reduced-error calculation of individual polytropic constants which may vary from cycle to cycle. This enables precise calculation of individual combustion event phasing, delivering information needed to affect the necessary correction in combustion-defining input parameters (e.g. intake pressure, injection timing, etc.), executed by the engine controller for use on subsequent combustion cycle on the same cylinder. The pressure filter construction is based on pattern recognition technique and guarantees equal performance regardless of engine rotational speed. The signal processing technique requires only invariant numbers of samples per combustion cycle to deliver excellent results in the angular span covering -180 thru +90 degrees with TDC firing being located at zero degrees. The performance of the technique is illustrated with experimental results involving calibration and testing of a gasoline direct injection compression ignition (GDCI) engine.