A heat transfer model for small-scale spark-ignition engines has been proposed by authors in previous study. However, that model was developed based on experimental data of one engine, it may not be so accurate for others. In order to improve the accuracy of predicted heat transfer rate for different engines, a modified heat transfer model using Stanton number based on two engines is proposed. Prediction results of instantaneous heat flux, global heat transfer, heat release rate, and cylinder pressure based on the proposed model are compared with the experimental results of three engines and prediction results of previous model. It is found that the proposed model has prediction results closer to the measured data than the previous models at the most engine operation conditions. (C) 2008 Elsevier Ltd. All rights reserved.