Skunk2’s Alpha Series Header for the 2012+ Civic SI / 2013+ Acura ILX offers a large 4-inch bellmouth design with a 3-inch outlet is manufactured from high quality cast stainless steel for superior heat resistance and strength. Heavy duty 1/2” thick flanges ensure secure and leak free attachments. Air flows smoothly through mandrel bent T-304 stainless steel and a high-quality stainless steel braided flex section. The one-piece design eliminates the need for the catalytic converter maximizing air flow and allowing for maximum power. Uses factory mounting locations for the OEM O2 sensors. No modifications are needed as it is a direct bolt-on unit to the OEM exhaust cat-back location.