Typically, the combustion analysis for S.I. engines is limited to the determination of the apparent heat release from in-cylinder pressure measurements, effectively using a single zone approach with constant properties determined at some average temperature. In this paper, we follow an approach consistent with the engine modeling approach (i.e., reverse modeling) to extract heat release rate from combustion pressure data. The experimental data used here solely consists of quantities measured in a typical engine dynamometer tests, namely the crank-angle resolved cylinder pressure, as well as global measurements of the A/F ratio, engine speed, load, EGR, air mass flow rate and temperature and exhaust emissions. We then perform a two-zone, crank-angle resolved analysis of the pressure data using variable composition and properties. Furthermore, the heat transfer correlation is iteratively tuned until the asymptotic burn mass fraction matches the combustion efficiency dictated by the exhaust gas composition. In this fashion, the analysis (reverse modeling) agrees will all measured data and in addition, the heat transfer correlation is “self-calibrated” for the engine tested and the operating conditions.This study included six engine operating conditions, reflecting the influence of load, engine speed and equivalence ratio. The procedure described above was very robust and always led to converged, meaningful results. Comparison of this two-zone analysis with the conventional single-zone apparent heat release analysis shows that significant differences in the heat release rate exists between the two methods, particularly near the end of combustion and at high load where the heat transfer is more significant. The methodology described in this paper can very effectively be used to analyze engine combustion data in a manner consistent with the engine modeling approach. The procedure described here is intended as an integral part of engine dynamometer tests for more rapid and accurate way of calibrating (and modeling) S. I. engines and providing a rapid evaluation of their combustion characteristics.