Concerns such as depletion of petroleum fuels and global warming are placing more severe demands on internal combustion engines each year for reduced fuel consumption and CO₂ emissions. Countries around the world have set regulations that drastically reduce CO₂ emissions from vehicle exhaust. In order to meet these requirements, various new engine technologies are being developed. One of the technologies to cut CO₂ emissions of the SI engine is the combination of reduced displacement, high compression ratio, forced induction, and direct fuel injection. But in this downsized engine, abnormal combustion, which occurs under the condition of low speed and high intake pressure, is a serious problem. It has been referred to as Super Knock, Mega Knock or Low Speed Pre-Ignition (LSPI). In this paper, we use the term Super Knock.Many research institutions and car manufactures have been investigating this abnormal combustion, but the exact cause is still unknown.The goal of this study is to investigate the cause of Super Knock using a 1.6L in-line four-cylinder SI engine with direct injection and turbocharging. By recreating Super Knock we investigated its sensitivity in terms of both engine parameters and spark plug characteristics. The results of these investigations are reported in this paper.