The objective of this project is to design and develop aerodynamically the undertray of a formula style car. This implies a whole design of a new undertray that fits well to the overall design and performance of the rest of the car. This design includes the length, size and shape of the inlets and outlets of the diffuser as well as the shape of the conducts. To Increase the downforce and decrease the drag to be the fastest is the maximum absolute of any motorsport. The objectives of this project are to: Test the ground effect influence on downforce. -Design iterations of diffusers to get the most aerodynamically efficient. -Optimize the diffuser geometry. -Design a whole undertray for the car. -CFD simulations of the whole car. To make all of this possible knowledge about CFD is needed. Therefore, 2D and 3D simulations of test cases and full car wind tunnel study will be developed.