aFe's Twisted Steel headers outflow and outperform the Ford diesel factory exhaust manifolds for a true, bolt - on performance header system. These precision - designed, hand - crafted headers are mandrel - bent from 1 - 34 into 2 heavy duty gauge .120 wall, brushed finish 304 stainless steel tubing and are 100 hand TIG - welded for strength and durability. Optimized tube lengths deliver true pulse control technology for improved flow and performance across the power band. Laser - cut, heavy duty head flanges are machined to match the exhaust ports for a secure seal. EGT ports with plugs, quality hardware and gaskets are included to ensure hassle - free installation and quality fit. Performance Gains Outflows factory manifolds by up to 7. Brushed Finish 304 Stainless Steel Construction Constructed of brushed finish .120 wall, 1 - 34 into 2 mandrel - bent 304 stainless steel tubing for strength and durability. Optimized Tube Lengths Tube lengths and mitered collectors are optimized for true pulse control technology which improves flow and performance across the power band. Heavy Duty Flanges These headers incorporate laser - cut, heavy duty flanges machined to match the exhaust ports for a direct - bolt on, leak - free seal. EGT Ports Two 18 NPT exhaust gas temperature (EGT) ports are incorporated. This allows for easy installation of sensors, gauges or testing equipment. TIG - Welded 100 TIG - welded for strength and durability. All aFe exhaust systems are engineered and manufactured in our Corona, California manufacturing facility.