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The demand for more efficient vehicles is growing worldwide. A promising technology is the engine downsizing plus turbocharging applied to gasoline direct injection, GDI, engines. In parallel with this technology, the use of lean mixtures on engines can be an extra opportunity to reduce fuel consumption. An experimental investigation was performed on an engine dynamometer to study the impacts of lean mixtures on the performance of a GDI engine. It was used a GDI 1.4L with turbo engine with a programmable engine control unit (ECU) to optimize the calibration for different air fuel ratios. The Engine was calibrated for maximum spark advance limited by knocking. Combustion duration, mass fraction burned and other combustion parameters were calculated based on in-cylinder pressure curve data. The combustion variability was analyzed from 900 recorded engine cycle for each operating condition. Results show that the use of lean mixtures can lead engines to improved efficiency.