When it comes to intake systems, the first company to come to mind is K&N, and for that reason it is no surprise that they are the industry leaders in the Inake market. Here is their Typhoon Intake System designed for the 2015 STI. This kit dramatically reduces intake flow restrictions while smoothing airflow for better performance and more horsepower. Other benefits include a nice throaty intake sound which is familiar under full throttle acceleration. Comes with an attractive red powder coated tube, an air filter box that fits right in place of the OEM unit, and a high flow filter that can be re-serviced after so many miles. If you have simple hand tools, this intake system can be installed in about 90 minutes. Expect average horsepower gains of around 34.32 HP @ 5400 RPM with a proper tune.