Skunk2's Alpha Series Header utilizes our race proven designs in a more affordable and accessible to everyday enthusiasts. As a result, the Civic 2012 Si header was the perfect candidate to add to this line. The large 4 inch bellmouth design with 3 inch outlet is manufactured from high quality cast stainless steel for superior heat resistance and strength. This design enables maximum extraction of air flow and increased power. Heavy duty 1/2" thick flanges ensure secure and leak free attachments. Air flows smoothly through mandrel bent T304 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. Bungs are also included for the OEM O2 sensors. No modifications are needed as it is a direct bolt on unit to the OEM exhaust cat back location.