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