The 21-815C Performance Cold Air Intake System produces horsepower and torque gains by replacing the restrictive air filter and air intake housing. This air intake system was designed, tuned and dyno-tested to fit specific Audi A4 models. The cone shaped AEM Dryflow air filter is made of a synthetic media which requires no oil and can be used up to 100,000 miles before cleaning (depending on driving conditions). The two piece heat shield keeps hot engine air from entering the air intake system and directs cooler air using the factory inlet scoop. It has been designed to have more air capacity than the factory unit for better air flow. A clear AEM logo also doubles as a window to monitor if the filter needs servicing. The factory vacuum tube mounts directly on the intake tube. The air intake system is backed by AEM's Lifetime Limited Warranty. Some AEM air intakes are not legal for sale or use in California and other states adopting California emission standards, while others are 50 state legal. View the 21-815C vehicle applications to determine the legal status for each vehicle.