B&B Exhaust is a complete stainless steel mandrel bent cat-back system. On an A4 the catalytic converter is bolted to the turbocharger and then the exhaust begins with the downpipe. Unlike most other aftermarket exhausts the Billy Boat exhaust includes a 2.5" downpipe. The exhaust then continues back to the innovative center muffler where it splits into dual 2.25" pipes. Each of these mandrel bent pipes goes to its own muffler with a 3.5" rolled round tip. This exhaust is very quiet and simply changes the tone of the exhaust to a deep unobtrusive sound. With TIG welding fully stainless construction and CNC'd hangers you will not find a higher quality system on the market.