Air Boxes

Is your engine drawing hot air from the engine bay, or do you want an air filter that is better shielded? An air box is an enclosed housing around the air filter that can route cooler air to the intake. This category includes both vehicle-specific kits and universal inline models for your project.

What does an air box do?

An air box encloses the air filter and separates it from the hot air in the engine bay. Cooler air is denser, which can give the engine better conditions, but the gain depends on the car, the engine and the rest of the intake. The box can also protect the filter against water and dirt – for example, BMC's kit for the Land Rover Defender 2.5L TD5 is available in a waterproof version. If you would rather shield an open filter, an intake heat shield can be an alternative.

How to choose an air box

• Fitment: Vehicle-specific kits such as the Weapon R Stealth Air Box for the Scion FRS or BMC's kits for e.g. the VW Polo V 1.4 GTI and Alfa Romeo GT 2.0 JTS are made for specific models. Check the model year and engine for the specific part number.
• Pipe diameter: Universal inline air boxes from Spectre are available in e.g. 4 and 5 inches with a filter and are fitted into an existing pipe.
• Air inlet: Where the box draws its air from typically matters more than its size. Placement, pressure drop and space in the engine bay need to work together.
• Connection: The connection to the intake must fit – Perrin Performance, for example, offers hoses between the air box and intake for the Subaru WRX/STi. See also intake tubes.

Changes around the mass airflow sensor can affect the engine management, so follow the manufacturer's instructions when fitting. Feel free to compare with cold air intake kits or the full range under air intakes and air boxes. If you have a turbo engine, turbo inlet pipes are often part of the same project.

Frequently asked questions

Do I need to replace the air filter when I fit an air box?

It depends on the product. Some air boxes come with a filter, such as Spectre's inline models, while others use a specific filter. Check the product description, and clean or replace the filter according to the manufacturer's instructions.

Can an air box matter at a vehicle inspection?

It depends on the product and the car. Changes to the intake can matter at an inspection, so check the approval and documentation for the specific part number before fitting the part to a road car.

What is the difference between an air box and a cold air intake kit?

An air box is the housing around the filter itself and can be used on its own or as part of an intake. A cold air intake kit typically also includes pipes and a filter and is designed to draw air from further away from the engine heat.