00-06 Wrangler TJ/LJ;4.0L 6 cylinder engine;1.5 14-gauge 409 stainless steel tubing;0.5 thick head flange;Merged collectors;50 State Legal CARB EO# D-550-12; California Residents: WARNING The new Twisted Steel performance header from aFe Power is redefining the header industry with new pulse control technology. aFe engineers have designed this header using optimum tube lengths and mitered collectors for maximum flow and velocity for power delivery across the entire power band. Combine with a large 1/2 thick head flange and 14-gauge 409 stainless steel tubing, you have a header that is strong and powerful. in recent dyno testing, this header produced 9hp and 10lbs. x ft. of torque. Twisted Steel headers are 100% bolt-on with no modifications necessary and are proudly engineered and built in Corona, CA.