Audi A4 Cold Air Intake is used to decrease the temperature of the air going into the engine.  What is the purpose for cooling down the airflow going to the engine.  Cooling down the engine temperature will help to increase the output of the engine by helping it to run most efficiently.  A Cold Air Intake will increase the horse power that your European car engine can put out.  The addition of the cold air intake will also increase the fuel economy as the engine runs more efficiently.  Stock air intake systems do not make the air cold and often have much too restrictive of flow in order to save space in the engine compartment and lower engine noise.  What a cold air intake will do is open up the flow really allowing the engine to breathe well.  Aftermarket cold air intake systems come in many different colors and sizes, and are easy to install when compared with other performance-increasing modifications.  

Cold Air Intake systems come in many different styles and can be constructed from plastic, metal, rubber (silicone) or composite materials (fiberglass, carbon fiber or Kevlar). The most efficient cold air intake systems utilize an airbox which is sized to complement the engine and will extend the power band of the engine.  How the cold air intake works is simple.  Since cool air is has a higher concentration of molecules per unit, the cold air intake in general works by inducing cool air from outside of the engine.  Although, the expression "cold air intake" is commonly used to describe other ways to increase the volume of oxygen into an engine.  

• ·      ·      ·      Methods of creating the cold air intake:
• ·      ·      ·      Allow for less restriction of flow by increasing the diameter of the cold air intake.
• ·      ·      ·      Using less resistant cold air intake materials.
• ·      ·      ·      Less restrictive air filters allow more airflow.
• ·      ·      ·      Creating the most direct path with the cold air intake.
• ·      ·      ·      Modifying the distance of the cold air intake to insure the most airflow at given RPM's.

Sometime in the late 80's, the aftermarket car parts company K&N created the first cold air intake system.  These intakes were made of plastic tubes and a cotton gauze air filter.  Not long after K&N's breakthrough of the first cold air intake, many other companies began springing up with their own version of the system.  Offering many styles of the cold air intake made from carbon fiber, plastic or metal tubing and coming in all different designs and colors.  This lead to new ways of customizing that was very specific to each vehicle and engine type.

The most simple cold air intake designs primarily swap out the factory airbox with a short plastic or metal tube that leads to an air filter.  These systems are referred to as short ram intake.  Depending on how limiting the factory airbox is will determine the actual horse power increase from using this method.  This filter is typically found directly in the engine bay.  The short ram intake will usually increase noise because of the increased airflow and reduction of insulation.  This style of cold air intake is popular although one of the more basic types.  

More involved cold air intake systems are have a much more technical design which use a heat shield to isolate the air filter from the heat coming out of the engine compartment.  This type of cold air intake system usually will bring cold air in from the front or side of the engine compartment for the best results.  In the higher end cold air intake systems, materials such as carbon fiber are used to reduce the weight of the car.  Even more advanced materials such as Kevlar can be used that will dramatically reduce weight in the engine.  Moreover, these materials have a much higher cost and are often more aesthetically pleasing than functional, unless of course we are talking about the most serious of race cars.