A comparison between the stock B6 A4 exhaust system and a Billy Boat 2.5" Sport Catback Exhaust. Both the stock and aftermarket exhaust were run without a catalytic converter (test pipe). For both runs, the car was run to be brought to normal operational temperature, previous to the video. My car is a 2003 Audi A4 1.8T Quattro with a 5 Speed Manual. The exact exhaust system is a Billy Boat FPIM-0506. The test pipe is a CTS Turbo 1.8T Test Pipe. The reason for the exhaust vapor in the second and video and not the first is because the first video was filmed in the summer, and the second video in the winter.