In the framework of a continuous strive for better engine efficiency, the Turbulent Jet Ignition technology presents itself as a valid option to decrease fuel consumption and emissions. Nevertheless, careful design and optimization is required to fully exploit the advantages of TJI combustion, with 3D/CFD analysis acting as a fundamental tool in this regard. The present work aims at the describing with 3D/CFD modelling and simulation a Turbulent Jet Ignition single cylinder engine. After describing the main features in TJI operation, a comparison between stochiometric and lean mixture conditions is presented. A calibration campaign, aimed at improving the reliability of the model, is then performed.