Function
The S4 liner has vents positioned directly behind the intercooler. The vacuum created by the spinning wheel draws air from the engine bay, causing more air to flow over the intercooler.

Part numbers
• 8D0821171G S4 driver's side wheel well liner

Comments
An easy DIY installation. Just undo the 11 Torx T20 screws and 2 flathead screws holding the stock liner, pop in the new liner and replace screws.