This study investigates the effect of injection timing on the high-load combustion performance of a split-injection strategy in a spark-ignition direct-injection (SIDI) engine. Performance parameters derived from in-cylinder pressure data are analysed alongside high-speed natural flame luminosity images in order to obtain relationships between engine output and flame propagation behaviour. Trends in parameters such as indicated mean effective pressure (IMEP) and total heat release are found to be multimodal; as early injections aid the mixture formation process whereas late injections may lead to an increase in turbulence intensity at the point of ignition. Analysis of the high-speed images provides a further explanation of the observed results through investigating flame propagation speed and global eccentricity (i.e. non-circularity).