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A short ram intake installed in a 2.0L 4-cylinder engine
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 power 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 parts come in many different colors and many different sizes.
HistoryThe 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 AEM, Airaid, Injen, True Flow, 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).
MechanicsAll 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 filter.
Disadvantages
Cold air intakes
hinder the evaporation of the fuel droplets
increase the risk of ice in the intake
and thus like all intakes need an electric heater for cold weather.
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). 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 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. 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.
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"
See also
SuperchargerTurbochargerBooster engineWarm air intakeRam-air intakeAir filterdiffuser (automotive)All text is available under the terms of the
GNU Free Documentation License. (See
Copyrights for details.)
