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Discussion Starter #1
Allright, newbie question #53

What's the poing of a cowl hood? Isnt the point of a scoop to catch fresh air, so if your driving forward air is being shoved into the air cleaner. So what's the point of the cowl hood if it's mounted the opposite way of a hood scoop. Doesnt the air hit the cowl, drifts over, hits the windshield, follows the slope of the windshield upwards and drifts over the car. How is it forced into the engine section? Or is it made just to look cool?






Mike
 

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Hard to believe, but the pressure at the base of the windshield is higher than at the front of the hood. It swirls around in this area, and you get more air.
 

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Discussion Starter #3
Hm....I take your word for it even though I still dont get it. The way I see it it's physically harder for the air to whirl around then to drift along the windshield. How is the pressure in the lower windshield formed? Does any cowl hood work? I noticed that you put a cowl hood on your blazer, did it have to be designed specifially for the high pressure to occur? So in a car that doesnt have cowl hood induction, does the air whirl around at the lower windshied?



Thanks,



Mike
 

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Cowl Hoods

Poncho hit it on the nose. There is a tremendous amount of pressure in the cowl area. The "cowl" hoods just like the Camaro's prior to 69 on the race cars found that the design of the hood if it had an opening created a large vacuum and air would flow thru the opening.
Remember the 69 Camaro had an ad out that called the system the Super Scoop. It was reffered to as Air Induction. In 1970 the Chevelle came out with "Cowl Induction" and the name has stuck ever since.
If a regular production car did not have a closed cowl area and weatherstrips under the hood to seal it then you would pick up a ton of stuff and find it in the engine compartment.
 

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Nightfire said:
Hm I noticed that you put a cowl hood on your blazer, did it have to be designed specifially for the high pressure to occur?
Yeah....gained 400 hp in the old 2.8.........................

No...J/K...........just an experiment with some sheet netal.

 

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Hey poncho, what yr model you got. Mines 85 and was thinking about a cowl hood for the 283 that Im puttin in mine. What kind of dimensions you got on the cowl.
 

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Mine is an 83...same hood.

I just bent up a piece of sheet metal and pop rivetted it on. It's about 20x40x 2 in high.
 

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Nightfire said:
Hm....I take your word for it even though I still dont get it. The way I see it it's physically harder for the air to whirl around then to drift along the windshield. How is the pressure in the lower windshield formed? Does any cowl hood work? I noticed that you put a cowl hood on your blazer, did it have to be designed specifially for the high pressure to occur? So in a car that doesnt have cowl hood induction, does the air whirl around at the lower windshied?





Mike
It is similar to how an airplane wing works.
 

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even the 70 chevelle ss ls6 big block only boasted a few h.p. gain. it was 90 percent hype and a two percent gain in power.
 

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lluciano77 said:
It is similar to how an airplane wing works.
Umm, sorta. An airplane wing uses Bernoulli's Principal to create lift. As the velocity of a fluid increases, its pressure decreases.

A wing, or airfoil, does this by curving the top and using a flat bottom. As the air passes over the top of the wing it accelerates and looses pressure, the air on the bottom of the wing is not accelerating, so it keeps the same pressure. This pressure deferential is what causes lift.

In the case of a cowl, the air builds up at the base of the windshield because it kinda has no where to go right away. At the leading edge of a wing the air is directed to either the top or the bottom. On a car, there is nothing to direct the air quickly enough over the vehicle. So the pressure builds. This can also be described as a form of parasite drag.

I guess this turned into an excuse for me to finally use all that information I leaned in those Aerodynamics classes.

:thumbup:

Chris
 

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The cowl induction hood only works past a certain speed. It is of no use at slow speeds. The 69 Z/28 had a solenoid operated flap that sealed the back of the hood. The solenoid was operated by a vacuum switch. When the cowl induction hood was shut off (slow speed) the air was taken from under the hood just like a traditional car. Put your foot in the carb and the cowl hood flap opened, or it was open under highway+ speeds. The iar moving over a hood and meeting the base of the windshield does not know where to go. Some of it spills over the top of the car, but a lot of it builds at the base of the windshield and boils off the sides. The cowl hood was designed to take advantage of this phenomenon.

Vince
 

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if you think about it when its raining and the wipers push the water down to the bottom of the windshield it doesn't shootback up the windshield so that would mean hat the wind would have to be swirling to stop the water from going back up the windshield, hope you could make sense of that \

my .02
 

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Air goes into the cowl scoop, it does not come out. I made a baffle for mine to let air in and keep water out.
Here is a shot of it in the making.
 

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Discussion Starter #17
Thanks guys:thumbup: I get it now, yet a forward facing scoop makes more sense to me....
But you cant argue that cowl hoods dont look good.







Mike
 
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