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A comprehensive modeling and visualization study of flow and combustion is reported for a production four-valve-per-cylinder homogeneous-charge four-stroke-cycle spark-ignited engine. Coupled port and in-cylinder computations are presented for five combinations of valve deactivation, valve shrouding, and cam profile. Motored (induction and compression) results are compared with transient-water-analog flow-structure visualizations. A new flamelet model for homogeneous-charge turbulent premixed combustion has been implemented for fired engine simulations. Several issues in the application of CFD to flow and combustion modeling in practical port-and-cylinder systems are addressed. These include numerical inaccuracy, elucidation of the role of induction-generated flow structure and turbulence, and new insights into premixed flame propagation.