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An Undertray is an aerodynamic downforce generator used in racing cars to enhance traction. It has the highest downforce to drag ratio among other aerodynamic devices. The objective of this study is to optimize the performance of a FSAE undertray through full vehicle three-dimensional numerical experiments. Based on Preliminary experiments, the basic undertray features are chosen. A simple sequential analysis approach is taken to study the downforce trends versus the variation of three undertray geometrical parameters. It is found that downforce generated is proportional to the diffuser angle until breakdown caused by separation of flow in the lower diffuser duct. A secondary diffuser guide vane is found to retard said separation, allowing uniform expansion at higher diffuser angles. Lower ground clearances cause boundary layer chocking and advanced separation. Finally the effect of the undertray on the aerodynamic wings is studied, and found to be negligible.