With customers swapping engines into a variety of platforms. While there are many turbo header options out there, many of our customers prefer to build their own or have a unique engine bay that requires custom headers. 1.875" primary tubes to 3" collector is the perfect header sizing for engines < 400 cubic inches and some slightly over. We use these EXACT materials in building headers for our own customer cars as well as our personal shop cars. Materials are MADE IN THE USA and proven to be of the highest quality and durability for use in even high demand applications.