An indirect method to map the burned gases in SI engine has been developed. It is based on visualisation by Laser Induced Fluorescence of the unburned mixture seeded with biacetyl. Both internally and externally recirculated burned gases are monitored. This diagnostic is complementary to the LIF technique applied to measure the gasoline distribution. These LIF gasoline and burned gases measurements are applied in a 4-valve optical access Sl engine for a large range of operating conditions. These include variations of both fuel injection and burned gas recirculation modes causing different types of stratification leading to very distinct heat release and exhaust emissions characteristics. Tumble level and spark location are also modified. The observation of the actual stratification in the engine forms a sound basis explanation of the engine performance. Parameters allowing an optimisation of NO, and HC levels can be inferred, and in particular the effectiveness of recirculation and fuel injection strategies. The conclusions are confirmed by measurements in a single engine cylinder conventional head with the same geometry.