A cold air intake is a device used to bring lower temperature air into a car's internal-combustion engine, to increase engine power and efficiency.
Standard air intake systems tend to be very restrictive, in order to eliminate engine noise. Aftermarket cold air intake systems come in many different colors and sizes, and are easy to install when compared with other performance-increasing modifications. All cold air intakes operate on the principle of increasing the amount of oxygen available for combustion with fuel. Because cooler air has a higher density (greater mass per unit volume), cold air intakes generally work by introducing cooler air from outside the hot engine bay. However, the term "cold air intake" is often used to describe other methods of increasing oxygen to an engine, which may even increase the temperature of the air coming into an engine.
Some strategies used in designing cold-air intakes are:
* increasing the diameter of the air intake, allowing increased airflow.
* smoothing the interior of the intake to reduce air resistance.
* providing a more direct route to the air intake.
* tuning the length of the intake to provide maximum airflow at certain engine speeds (RPM).
* using a more efficient, less restricting air filter.
* cold air provides more oxygen for the engine to burn.
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Disadvantages
* hydrolock - The intake is lower, and more likely to introduce water into the engine when fording streams or flooded roads. Hydrolock generally does not occur unless the filter is fully submerged in water."Bypass filters" can be purchased which prevent any water of any kind from entering the engine.
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Application
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 intake systems utilize an airbox which is sized to complement the engine and will extend the powerband of the engine. The intake snorkel (opening for the intake air to enter the system) must be large enough to ensure sufficient air is available to the engine under all conditions from idle to full throttle. Under some conditions intake system efficiency can be lost if the intake opening for the airbox is too large.
The most basic cold air intake replaces the stock airbox with a short metal or plastic tube leading to a conical air filter, called a short ram air intake. The power gained by this method can vary depending on how restrictive the factory airbox is. The placement of the filter is usually directly in the engine compartment. The overall benefits depend on the specific application. Power may be lost at certain engine speeds, and gained at others. Because of the increased airflow and reduced covering, intake noise is usually increased. This effect is usually amplified on applications where a resonator, a part intended to reduce intake noise on some vehicles, is replaced by the intake.
Well designed intakes use heat shields to isolate the air filter from the rest of the engine compartment, providing cooler air from the front or side of the engine bay. Some systems called "fender mount" move the filter into the fender wall, this system draws air up through the fender wall from below the car, which provides even more isolation and still cooler air. Carbon fiber can be used for the piping instead of metal, reducing weight and insulating the air from the engine bay in some cases. Carbon fiber and other advanced composites (such as Kevlar) are expensive, and can be more aesthetic rather than functional.
Air bypass valves are gaining popularity in cold air intake manufacturing. An air bypass valve is a filtered spacer that is positioned more into the engine bay, between two connected pieces of the cold air intake assembly. This prevents hydro-locking by providing an alternate route for air to come in, thus eliminating the vacuum that causes water to be sucked in from a puddle. Foam filters are a simple piece of foam that is air permeable, and most have no valve. It is argued that this reduces power, but in actuality it provides more surface area for air to enter the engine when the driver accelerates. When driving at moderate speeds, the suction caused by the engine is not enough to activate the air bypass valve. Cloth filter bypass valves only allow air in if the valve is sucked open as result of the vacuum pressure caused by a blocked filter at the bottom of the intake. When it comes to cold air intakes this is the "best of both worlds".
