Your engine needs to get as much oxygen as it can in order to perform to its maximum potential. One of the best ways to maximize the amount of oxygen entering your motor is to make sure that the air coming in through the intake is as cold as possible. Cold air is denser than hot or warm air, and this extra density translates into a lot more oxygen per cubic foot.

Your sport compact car might be outfitted with a smaller, 4-cylinder engine. These engines rev fairly high, making the ability to draw in as much cold air as possible a priority. One really simply and inexpensive way to chill out the air hitting your engine is to install something called a cold air intake. This intake is designed to replace the factory air filter, and a section of the intake piping that is usually located towards the front of the car.

Boiling it down, there are three different concepts underlying a cold air intake's design. The first is the piping. Most intakes are created in order to form the straightest path possible from the air filter to the intake. Obviously, in some vehicles engine bays are cramped and some curvature is required, but in general, designers attempt to limit 90 degree curves in the pipe that may impede air flow.

The second concept is the idea of an open element air filter. Your car's stock air filter is protected inside of what is called an air box. This helps to keep it from getting too dirty, but it also muffles the noise of the air intake, making for a pretty uninspiring sound when you rev the engine. A cold air intake usually uses a cone filter which is not enclosed, allowing it to draw air from all sides. These filters, as in the case of companies like K&N, are washable and contain a thin layer of oil that helps trap dirt. The airflow of these cotton filters is also usually greater than a stock paper filter, so you end up trading a bit of engine protection for increased oxygen.

The third, and probably the most overlooked aspect of a cold air intake, is placement. You might have seen some kits installed in such a way that the filter is simply dropped directly into the engine bay. This can actually reduce the performance of your motor, because the air near an engine is quite hot, and does not contain nearly as much oxygen as air from the outside. If you want to place the filter inside your engine bay, you can but you need to take steps to ensure that it is insulated from engine heat.

You can do this by building a small enclosure that makes a seal with the hood when closed and keeps hot air from reaching the intake. You also want to make sure that there is a flow of fresh air from outside the car that is actually directed towards the filter itself. Some people install the filter outside the engine bay, in one of the front fenders or just underneath the front bumper. This can be risky, as large puddles of water can force moisture into the intake. Filters in this position also tend to get dirty much more quickly. It's really up to you how comfortable you are with your air filter's position.

Cold air intakes are an inexpensive way to add a little bit more performance and a much more aggressive sound to your compact car.