aFe Twisted 1-3/4in 304SS Shorty Header 20-23 GM 2500/3500HD 6.6L V8aFe Twisted 1 3 4in 304SS Shorty Header 20 23 GM 2500 3500HD 6. 6L V8 1 3 4" 304 Stainless Steel Construction: This system is constructed of 1 3 4" mandrel bent 304 stainless steel tubing for maximum strength and durability. Powerful Sound: This system produces a powerful sound unleashing all available horsepower and torque. Installation: Utilizing factory style flanges this system is a direct bolt on system, which requires no cutting or modifications