This SET of universal splitter diffusers can be mounted in many different splitter types to create a "3D" undertray.
Tunnels create a venturi effect under your splitter and pull more air out from under the area that is directly under the high-pressure splitter area. This makes significantly more downforce than a regular flat undertray. It's not uncommon to double the downforce of a splitter with diffuser tunnels like these.
Please be sure to attach these tunnels securely and with washers they can and have ripped themselves out of splitters from the forces they create.
