A new reaction scheme for NOx production is incorporated into a steady state quasi-dimensional engine combustion simulation. The reaction kinetics includes 67 reactions and 13 chemical species, and assumes equilibrium concentration for all other chemical species. The General Engine SIMulation (GESIM) developed by Ford Motor Company is used to model the engine cycle. The new reaction scheme is a super-extended Zel'dovich mechanism (SEZM) which predicts NOx formation levels to within 10% of engine test data for several engines, whereas the 3 reaction, extended Zel'dovich mechanism (EZM) is shown to have errors of approximately 50% or more for similar conditions. Analytical engine mapping, under NOx constrained calibration, requires accurate modeling of NOx emissions over varying engine operating conditions. A methodology for performing an analytical engine map will be presented and the benefits of the SEZM will be shown, as well as a detailed comparison with the EZM for two complete engine maps.