2k2nyc check out www.strasmosphere.com, the make a cold air induction unit for the V8 S4 and the A43.0. Some of the guys on the forums will tell you the Audi's stock air box is sufficient and I agree, it's just a personal preference. I purchased mine about a year ago and I'm satisfied with it. There aren't too many companies making this kit for our cars.
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'03 A4 3.0 QM SP Milltek Hyperflow intake WKR chip B&M Short shifter Brushed Alu mirrors De-Badged Painted lowers
Dude i just bought the biggest k&n cone filter that could fit where the feactory intake box was out. and it actuallly did make a difference and it cost me 50 bucks and im about to go get the lil cone for that other lil pipe sticking up. but i think it was worth it and it sounds soo meannnn at WOT.
02 Audi A4 3.0 quattro -K&N filter -Debadged -5% Tint in the front -15% Tint in the back -Alpine head unit w/custom dash install -2 12's with 1200 watt amp