Originally posted by turboHLS30
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A ram-air intake is any intake design which uses the dynamic air pressure created by vehicle 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 pressurize a series of cells to provide the aerofoil shape.
At low 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. The lack of losses also means without heating the air. Thus a ram-air intake also is a cold air intake. In some cars the intake is placed behind the radiator, where not only the air is hot, but the pressure is below ambient pressure. The ram-air intake effect may be small, but so are other mild tuning techniques to increase cylinder filling like using larger, fresh air filters, high flow mass flow sensors, velocity stacks, tuned air box and large tubes from the filter to the engine.
Principle: Ram Air is the effect whereby air is encouraged to enter the engine at a much higher rate than would be expected through the mechanical action of the engine by itself. This is similar to the effect of forced induction, but without the need for a turbo or supercharger.
Fact: Cold air is denser than hot air and therefore takes up less space. As such, if your engine can ingest cooler air, more air can be mixed with more fuel, which in turn provides more power. An additional benefit is that cooler air has a higher resistance to knock, allowing more ignition timing advance, or “boost” in supercharged applications. Either way, they both equal more power. This is the theory behind cold air intakes, ice on the manifold, intercoolers, manifold insulators, etc.
Solution: One possibility for reducing intake air temperature is to install an aftermarket cold air intake, Another less expensive option is to draw-in, or “ram”, more cold air from an outside source. This is the idea behind the Ram Air Performance System.
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