A cold air intake is a System used to bring down the Temperature of the Air going into a car for the purpose of increasing the of the Internal-combustion engine. A secondary goal is to increase the appeal of a car by changing the appearance of a car's engine bay and creating an attractive intake noise. These Aftermarket (automotive) parts come in many different colors and many different sizes.
The aftermarket company K&N Engineering first offered air intake systems in the late 1980s. Those intakes consisted of rotationally-molded plastic intake tubes and a conical, cotton gauze air filter. In the late 1990s a proliferation of intake manufacturers such as Injen, AEM, Airaid, True Flow, AFE (advanced FLOW engineering) and Volant entered the fray. In addition, oversea manufacturers imported their designs lending to the popularity of Japan domestic market (JDM) air intakes in sport compact markets. K&N and many of the other intake companies now offer intake systems in metal tube designs, allowing a greater degree of customization (the tubes can be powder-coated or painted to match a vehicle).
All cold air intakes operate on the principle of increasing the amount of Oxygen available for Combustion with Fuel. Because cooler air has more density for a given 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.
Intake systems come in many different styles and can be constructed from plastic, metal, rubber (silicone) or composite materials (fiberglass, carbon fiber or kevlar). Due to the limited time air actually remains inside the intake tubing, the materials often do not impact a kit's ability to deliver cool air. The most efficient intake systems utilize an airbox which is sized to compliment 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. If the intake opening has an unrestricted opening - no screens or other obstructions - the opening need not be larger than the inside diameter of the engine's throttle body, airhorn, or carburetor throat. 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. 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.
The most extreme designs, sometimes referred to as Complete Cold Air (CCA) intakes, route air from outside the engine bay, usually from the wheel wells, front grill,or a hood scoop. The intake can be placed such that the forward motion of the car pressurises the air coming in, creating a Ram-air intake. These intakes often require additional modifications and can require body modifications or replacement panels, such as a replacement "ram air-style" hood. Complete Cold Air intakes can convert to short ram intakes for winter or wet driving.-
When using a cold air intake, there is a potential risk when driving in the rain. This is often referred to as "hydrolock", and according to the automotive portal, MODsearch:
"Say it's raining cats and dogs and you're out for a spin in your car. Normally you'd love to rip through puddles without thinking twice, but because your engine is now getting air from inside your bumper you have to be careful. If your engine manages to suck up any amount of water through the intake and into the engine you will probably have little to no horsepower left. In more extreme cases, the water brought into the engine through the intake can actually break connecting rods in the pistons, as water will not compress at all, unlike air. In other words, be careful."It is important to take precautions when using a cold air intake as to avoid getting water in the engine. This may include installing a water shield in the intake or not driving in the rain at all. It is also notable that less damage will occur from water reaching the engine on a rotary engine car, as opposed to a piston engine car. Some cold air intake manufacturers now include a built in hydro-shield, a piece of plastic that blocks water from entering the air filter. K&N also offers a "sock" called the "Drycharger", which prevents hydrolock. These precautions are unnecessary for the most-part however, because for water to enter you intake manifold your filter would have to be almost fully submerged with water for an extensive period of time.
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 presses the pedal. When driving at moderate speeds, the suction caused by the engine is not enough to activate the air bypass valve. Cloth filter bypass valves actually have a valve, air only enters 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"
- Booster engine
- Warm air intake
- Ram-air intake
- Diffuser (automotive)