Rear Diffuser - Subaru WRX/STI 14-20It bolts underneath your existing mounting, you simply need to drill two more small holes each sides. Its four fins perfectly fits the shape of the factory valence, so it looks like it's almost part of it. The fins are precisely CNC machined and are bolted on the base plate without any visible hardware once installed. *The car pictured have the side diffuser option. You could save some money by combining them with the rear diffuser ! See more about