AEM introduces its new Cold Air Induction System for the 2005.5-08 Audi A4 2.0L Turbo part # 21-681. The largest power gains for the 21-681 are 4.7 horsepower at 2,500 RPM and 8.7 lbs/ft of torque at 2,500 RPM as measured on the company’s Mustang Dynamometer.