I have a S3 engine in my A4 avant with front mount intercooler and stage 1. Still running standard exhaust system (noticeably small). There's a lack of aftermarket exhausts out there for the b7 so thought I would try a free mod - removing the pre cat which is straight after the turbine housing. Easy access for us Audi A4 guys all done from the top of the car. Upon removal cat still visible. Started drilling it with a 10mm bit and it's soft as ****. It fell out after 2 minutes. Re-fitted it. Slightly deeper exhaust note, and after 4K RPM it's very noticeably quicker. My *** Dyno says 15bhp easy. Wish I would of done it sooner! Took me about 2 hours in total. Also no warning lights either.