Air Filter Basics
Air filter prevents abrasive particulate matter from entering the engine's cylinders, where it would cause mechanical wear and oil contamination.
Most fuel injected vehicles use a pleated paper filter element in the form of a flat panel. This filter is usually placed inside a plastic box connected to the throttle body with an intake tube. Older vehicles that use carburetors use a cylindrical air filter. This is positioned above the carburetor, usually in a metal or plastic container which may incorporate ducting to provide cool and/or warm inlet air, and secured with a metal or plastic lid.
Pleated paper filter elements are the nearly exclusive choice, because they are efficient, easy to service, and cost-effective. The "paper" term is somewhat misleading, as the filter media are considerably different from papers used for writing or packaging, etc. There is a persistent belief amongst enthusiasts that paper filters flow poorly and thus restrict engine performance. In fact, as long as a pleated-paper filter is sized appropriately for the airflow volumes encountered in a particular application, such filters present only trivial restriction to flow until the filter has become significantly clogged with dirt.
Oil-wetted polyurethane foam elements are used in some aftermarket replacement air filters. Foam was in the past widely used on small engines such as lawnmowers and other power equipment, but automotive-type paper filter elements have largely supplanted oil-wetted foam. Depending on the grade and thickness of foam employed, an oil-wetted foam filter element can offer minimal airflow restriction or very high dirt capacity, the latter property making foam filters the popular choice in off-road rallying and in motorsport where high levels of dust will be encountered.
Oiled cotton gauze is employed in a small number of aftermarket automotive air filters marketed as high-performance items. In the past, cotton gauze saw limited use in original-equipment automotive air filters.
An oil bath air cleaner consists of a round bowl containing a pool of oil, and a round insert which is filled with fibre, mesh, foam, or another coarse filter media. When the cleaner is assembled, the media-containing body of the insert sits a short distance above the surface of the oil pool. The rim of the insert overlaps the rim of the base bowl. This arrangement forms a labyrinthine path through which the air must travel in a series of U-turns: up through the gap between the rims of the insert and the base bowl, down through the gap between the outer wall of the insert and the inner wall of the base bowl, and up through the filter media in the body of the insert. This U-turn takes the air at high velocity across the surface of the oil pool. Larger and heavier dust and dirt particles in the air cannot make the turn due to their inertia, so they fall into the oil and settle to the bottom of the base bowl. Lighter and smaller particles are trapped by the filtration media in the insert, which is wetted by oil droplets aspirated thereinto by normal airflow.
Oil bath air cleaners were very widely used in automotive and small-engine applications until the industry adopted the paper filter in the early 1960s. Such cleaners are still used in off-road equipment where very high levels of dust are encountered, for oil bath air cleaners can sequester a great deal of dirt relative to their overall size, without loss of filtration efficacy or airflow. However, the liquid oil makes cleaning and servicing such air cleaners messy and inconvenient, they must be relatively large to avoid excessive restriction at high airflow rates, and they tend to increase exhaust emissions when used on spark-ignition engines.
Air intake systems allow your car to breathe easier creating more horsepower and greater mileage. Air intake systems have different styles to choice from, such as open element intake systems, sealed intake systems, and ram intake systems.
Let look at the most viaable aftermarket replacement,
Cold air intake
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.
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 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. The intake opening need not be larger than the inside diameter of the engine's throttle body, or carburetor throat, if it is larger then this may cause loss of efficiency under some conditions.
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.
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"
Warm air intake
A warm air intake is a system to decrease the amount of the air going into a car for the purpose of increasing the fuel economy. All warm air intakes operate on the principal of decreasing the amount of oxygen available for combustion with fuel. Warm air from inside the engine bay is used opposed to air taken from the generally more restrictive stock intake. Warmer air is less dense, and thus contains less oxygen to burn fuel in. The car's ECU compensates by opening the throttle wider to admit more air. This, in turn, decreases the resistance the engine must overcome to suck air in. The net effect is for the engine to intake the same amount of oxygen (and thus burn the same amount of fuel, producing the same power) but with less friction losses, allowing for a gain in fuel economy, at the expense of top-end power.
A ram-air intake is any intake design which uses the dynamic air pressure created by vehicle's motion to increase the static air pressure inside of the intake manifold on an engine, thus allowing a greater massflow through the engine and hence increasing engine power.
The ram air intake works by reducing the intake air velocity by increasing the cross sectional area of the intake ducting. When gas velocity goes down the dynamic pressure is reduced while the static pressure is increased. The increased static pressure in the plenum chamber has a positive effect on engine power, both because of the pressure itself and the increased air density this higher pressure gives.
Ram-air systems are used on high performance vehicles, most often on motorcycles and race cars. Ram-air has been a feature on some cars since the late sixties, but fell out of favor in the seventies, and has only recently made a comeback. Modern parachutes use a ram-air system to pressurise a series of cells to provide the aerofoil shape.
At low speeds (subsonic speeds) increases in static pressure are however limited to a few percent. Given that the air velocity is reduced to zero without losses the pressure increase can be calculated according to:
dP / P = (v2) / (2RT)
2001 7.3 XLT
4" straight pipe
TS 6 pos
Over Boost Annihilator
Edge monitor screen
Just my little ranch truck
Last edited by Gold 7.3; 01-03-2011 at 04:18 PM.