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« on: December 28, 2016, 05:02:01 AM »
Cowl Plenum and Cowl Induction Air Cleaner Systems use the high pressure area at the windshield to provide a very small "supercharger" effect but more then that is the effect of air temperature.
Cooler intake air makes more power.
Chevy used cool air intake systems on many cars and trucks in the 1980s with the Q-jet 4BB and other induction systems. It was just an air hose from the grill to the air cleaner but it works.
here is some info found online I thought was pretty good.........
Air scoops of various kinds are a common feature on cars with performance pretensions. Many scoops are purely cosmetic, but those that aren’t typically serve one or more of the following functions:
COLD AIR INTAKE
Burning fuel requires oxygen. Unless an engine carries its own oxygen supply (as with a rocket engine), that oxygen must come from the surrounding air. The amount of oxygen available to burn — and thus the engine’s maximum power output — depends on ambient temperature and local static atmospheric pressure. As a rule, cooler, denser air will yield more power while warmer, thinner air (such as on a hot day or at high altitudes) yields less.
The engine compartment of the average automobile tends to be very warm indeed. The normal operating temperature of the typical water-cooled passenger car engine is well above 160 degrees Fahrenheit (71°C) and an air-cooled engine may be considerably hotter. The heat radiated by a running engine quickly heats the air around it. Since most automotive engine compartments are enclosed and rather cramped, with few opportunities for the heat to escape, the air in the engine compartment is usually significantly hotter than the outside air. If the engine draws its intake air from under the hood, the high temperatures will reduce the density of the intake charge and thus reduce the engine’s net power output.
An obvious solution to this problem is to add a cold air intake channel that allows the engine to draw its intake air from the cooler, denser air outside the engine compartment. An effective cold air system can counteract much of the power loss caused by high under-hood temperatures, potentially improving engine output by 5% or more.
Simply cutting a hole in the hood does not a functional cold air scoop make. To be effective, a cold air intake (a) must be located in a high-pressure area of the hood; (b) must be designed in such a way that it actually allows outside air to pass through the inlet; and (c) must have a tightly sealed connection to the air cleaner and intake manifold so that the engine will breathe through the scoop rather than drawing some of its air from under the hood. The distance from the scoop to the air cleaner must also be as short as possible — the greater the distance the incoming air has to travel, the hotter it will get, both through friction and through absorbing engine compartment heat. A poorly designed or badly placed cold air scoop can be worse than useless, costing power by restricting the flow of engine air.
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