Description Reviews Milltek Header w/ Test Pipe for MINI Cooper S Traditionally thought of as a downpipe. The stock manifold/downpipe/cat is the biggest bottleneck in your exhaust system. An easy bolt-on installation that comes with all needed hardware & gaskets that need replacing. Removes all cats for highest flow. Can be installed with your stock exhaust or with a Milltek Sport unit (or any other aftermarket exhaust). This header will cause a check engine light of P0420 due to no cats and is designed for off road use. Car needs to be tuned to take full advantage of the performance and to turn off the check engine light. May not be legal in some states, Will also make the car very loud depending on what exhasut you already have.