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Cowl *IN*duction... (archive)

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Posted by Zandr on April 20, 2000 at 13:42:34:

In Reply to: Cowl induction... posted by Justin on April 20, 2000 at 12:27:22:

: Cowl induction isn't usually an intake method,

Yes it is, it's called INduction for a reason.

but simply an air system using the vacuum effect created by air travelling over the car. As the air travels over the car, a vacuum is created around the car (thus explaining why a piece of paper can be "sucked" out of an open window).

Depends where on the car you put the piece of paper. You're right that there's typically lower pressure outside a side window than inside the car, hence the tendency for your change from bridge toll to get sucked out the window when you do a max. acceleration test leaving the toll plaza. ;)

: A cowl hood simply creates an opening near the windshield in order that this vacuum effect can actually "suck" the hot air from under the hood, out... thus being replaced with cooler, atmospheric air from any frontal source.

Nope. On 99% of the cars out there, there is a high pressure area at the base of the windshield. The windshield is closer to vertical than the hood, so when the airflow across the hood hits the windshield, the air "piles up" (I know, but I don't feel like writing a dissertation on fluid dynamics.) creating a high pressure area. Cowl Induction takes advantage of this source of cool air for the intake charge.

: I've never known anyone that thought of cowl induction as an intake method... kind of an interesting thought, though. I am pretty sure that the point of most cowl "induction" systems is to keep ambient engine temperatures low.

Then you've never a)known anyone who knows what the phrase "Cowl Induction" means, or b) looked under the hood of a Chevelle. There's a pan that seals to the hood around the air cleaner to pull air from the Cowl Induction vents.

: I suppose perhaps you were confused by the term "induction"...? It doesn't mean the same thing here as in the term "forced induction". Cowl induction is inducing air into the engine bay, not NECESSARILY into the engine.

You've just contradicted yourself, but you got it right this time. You're pulling air INTO the engine bay through the cowl induction intake. If you're doing it right, you pull the air directly into the intake. You're right in one respect, though. The pressures involved are much, much smaller than forced induction, on the order of inches of water, not PSI. As such, the "pressure" really just ensures that cool air is flowing IN to the engine bay through the cowl vents, and not the opposite.

: I suppose, though, on the older American blocks, it was able to accomplish both with the top-side, cylinder intake systems of the early hot rods. However, that was primary a coincidence.

No, it was the design. Plain and simple.

Cowl induction, now-a-days is primarily used to keep engine temps down... it's been that way since the inception of modern fuel injection and throttle bodies.

Uhh, no. Cowl induction now-a-days is primarily used for cabin air intakes. This is why you get a nice breeze through the vents when the car is in motion. It's also sometimes used indirectly to lower intake charge temperatures by lowering the engine bay temperatures. Underhood temps don't have a lot to do with engine temps; that's the radiators job, and only fairly exotic race cars use anything like cowl induction to push air through a radiator.


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