A spark-ignition (SI) engine cycle model was used to study the effects of spark plug location on a twin-spark plug SI engine performance. A two-zone quasi-dimensional combustion model with a spherically developing flame propagation assumption was applied. Constructed simulation can be used for either single- or twin-spark plug configuration. For the twin-spark arrangement, spark plugs were considered to be located diametrically opposite to each other on cylinder head axisymmetrically. According to dimensionless distance from the cylinder center to spark plug location on cylinder head, r(sd) = r(s)/R, five locations (r(sd) = 0, 0.25, 0.50, 0.75, and 1.0) were considered. Inevitably r(sd) = 0 corresponds to the singles-park arrangement that the plug is located at the center. To comparison, single-spark plug configurations were also considered for other selected spark plug locations. From the result of the study it was found that centrally located single-spark plug arrangement gives the best engine performance and fuel economy, while for the all the other spark-plug locations away from the center twin-spark arrangement favorable to the single-spark plug configuration. (C) 2009 Elsevier Ltd. All rights reserved.