The CTS B5 A4 1.8T High Flow Cat Pipe is the premier cat pipe for your Audi. \n \nOur test pipe is designed to seamlessly fit in place of your restrictive stock catalytic converter; which is situated immediately after the turbocharger. Our test pipe 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 from installing our test pipe. 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 test pipe. 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" test pipe 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 \n1997-2001 B5 Audi A4 1.8T \n \nProduct Details: \n \n \nT304 stainless steel construction \nMandrel bent stainless steel \nFully tig welded design \nInstall hardware included \nGreat power upgrade \n \nTo remove the CEL that will occur; proper tuning software must be used. Use of stage 2 software upgrade is strongly recommended.