There are many types of aftermarket air intake systems, from the simple and inexpensive to the elaborate. But first let's examine why these systems are in so much demand by car enthusiasts. Aftermarket air intake systems increase airflow to your engine. This is desirable because increased airflow allows your engine to burn more fuel, and more fuel equals more power. An engine operates most efficiently with a mixture of 14 parts air to one part fuel, also known as the stoichiometric air/fuel ratio. So, if more air is supplied to the engine, more fuel can also be burned. More air and fuel (in the proper ratio) in the combustion process means a more forceful explosion driving the pistons, resulting in more power to the wheels.
The easiest way to improve airflow to your engine is just by changing your stock air filter to an aftermarket performance air filter. These filters are made of cloth or synthetic material instead of paper and will increase airflow without any decrease in the filtration efficiency that is so critical to the long life of your engine. However, although these filters will increase airflow because of superior material, airflow can also be improved by increasing the physical size of the air filter, but the amount of air these filters can flow is limited by the size of the stock factory air box. The one exception to this is the aFe IRF Performance air filter. The unique inverted design of this filter maximizes the use of the available space inside the factory air box, allowing the installation of a filter with up to 76% more surface area in the same location.
The next step in increasing air flow is to remove your factory air box to allow the use of a large, free flowing conical air filter. The simplest and least expensive air intake kits are little more than an air filter, but they are very effective because of the dramatic increase in the filter surface area. The filter in systems like the K&N 57i Series Induction Kit or the aFe Stage 1 Air Intake Kit connects to a universal flexible tube or to the factory air intake tube. The aFe system also includes a one piece heat shield that installs in place of the air box and seals against the hood, to help shield the filter from engine heat.
Airflow can be increased further by replacing your stock air intake tube. Most factory tubes make awkward bends and have sound baffles, which may inhibit noise but also restrict airflow. Aftermarket air intake tubes are usually constructed from mandrel-bent aluminum or molded polyethylene. While polyethylene has a slight advantage in that it can be molded asymmetrically, both types feature larger diameters and smoother bends than the stock, factory unit, for less restriction and greater airflow all the way to the throttle body or turbocharger. These air intake systems are sometimes referred to as "short ram" systems; they replace the factory air box and air intake tube, but the parts are installed in approximately the same location. Because they fit entirely within the engine compartment, they are generally easier to install. Variations of this type of system are made by AEM, aFe, AIRAID, Injen, K&N, Volant and Weapon-R. Some manufacturers, notably aFe, AIRAID and K&N, supply heat shields with their systems that shield the filter from engine heat. Most of these are designed to seal against the hood when it's closed, effectively creating an air box that allows the filter to take in cooler air, away from the engine. Companies like Injen and Volant enclose the air filter in an air box of their own design for some applications. Systems with heat shields or proprietary air boxes are usually referred to as "cold air" intake systems. As we'll explain in more detail shortly, cold air is denser and better for combustion, but cold air here can best be described as air that is cooler than the air under the hood. The most serious cold air systems position the air filter completely out of the engine compartment, usually behind the bumper. These systems are more expensive and their installation is certainly more involved, but the payoff is that now the air filter can really take in cold air, or at least air at ambient temperature. Cold air is denser and contains more oxygen. It's the oxygen in the air that combines with the fuel for combustion, so if the increased airflow is also cooler, more fuel can be burned resulting in even more powerful combustion. It's estimated that for every 10 degrees cooler the air intake charge, power will increase by 1 percent. Cold air systems like these are made by AEM, aFe and Injen. However, it should be noted here that in extensive dyno testing, AEM found that some vehicles actually performed better with a short ram system.
Positioning the air filter behind the bumper makes it vulnerable to water during extremely wet weather, so these cold air systems are usually made with the intake tube in 2 pieces, with the junction in the engine compartment. When desired, the air filter and the lower intake tube can be removed, and the air filter reinstalled at the end of the engine compartment intake tube, effectively converting the system to a short ram intake.
Another method of channeling cool air to the engine brings the cool air to the air filter, which remains in the engine compartment. One end of a scoop or flexible tube is connected to the air filter or air filter box and the other end is positioned in front of the vehicle. Such systems are sometimes referred to as "ram air" intakes if the opening is positioned where it can take advantage of high pressure areas in front of the vehicle, to force cold air into the air intake system. These scoops are available from aFe, K&N, Volant and Weapon-R.
Finally, while not an air intake "system", another way you can improve airflow to your engine is with a throttle body spacer. These are offered by aFe, AIRAID and Volant, and while the specifics differ, each installs between the throttle body and intake manifold and creates turbulence as the incoming air passes through the throttle body. This turbulence carries right into the intake port and helps to completely atomize the fuel charge as it's added to the incoming air. This improves combustion and increases engine efficiency. There's an aftermarket air intake system for every budget and every application. Even if you have a hot rod or custom car, or if your car's just not listed in a catalog, you can still get a quality system. For example, AIRAID's U-Build It intake system includes a performance air filter, an air intake tube you cut to fit, and all the necessary hardware and connectors to make a custom system. Everyone, regardless of vehicle, can benefit from an aftermarket air intake system.