The CTS B6 A4 1.8T High Flow Cat Pipe is the premier cat pipe for your Audi. \n \nOur high-flow cat is designed to seamlessly fit in place of your restrictive stock catalytic converter; which is situated immediately after the turbocharger. Our high-flow cat features 3" stainless steel piping; smooth mandrel bends; two 02 sensor bungs with an option for a third. Substantial power gains; improved exhaust flow and a more throaty sound are the main benefits of installing our high-flow cat. Upon inspection you will notice a flare which is nearly 4"; this flare then tapers to 3" and is designed to allow for optimal flow as the exhaust gas transitions from the turbocharger to the high-flow cat. In addition to being one of the best bang for the buck performance upgrades for A4 owners; our cat pipe is also a very attractive piece. Each 3" high-flow cat is mandrel-bent; hand tig welded. Do you need an additional 02 bung for data logging? Well; that's no problem! Tig welding additional 02 bungs can be done for an additional charge. \n \nFitment: \n \n2002 - 2005 B6 Audi A4 1.8T \n \nProduct Details: \nT304 stainless steel construction \nMandrel-bent stainless steel \nFully tig welded design \nOptional third 02 bung \nInstall hardware included \nGreat power upgrade \n \nTo remove the CEL that will occur; proper tuning software must be used. The use of stage 2 software upgrade is strongly recommended.