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Discussion Starter #1
Hey sup guys, I was wondering if someone could shed some light on how vented hoods work specifically.

I have been looking at CF hoods, and I wonder about validity of some of the designs, as they pertain to heat extraction...

I was always under the impression that a vented hood, any vented hood, similar to the C-West or HKS Kansai hood (we'll dub this a reverse vented), would draw air out through the opening on the top, while also helping air to vent through the radiator.

A buddy of mine says that sense the air is low-pressure in the engine bay, that a vent does the opposite, and thus, air would rather flow into the low-pressure zone, and exit whereever it can (presumably the bottom of the car), in effect, air is not vented from the top, but pulled in from the top.

He also stated that improperly designed hoods (his case in point the Shelby GT500 Mustang) can actually HINDER cooling and work negativley for heat extraction, while it looks like it'd do the job, it apparently doesn't.

Is there a definitave answer on how these work? Which ones do you guys know work and which ones are merely asthetics? I would rather pay 1200 for a working hood than 600 for a non working version that won't do jack for under-hood temps.

Thanks!
 

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Nygmatic
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with reverse vents behind the radiator air is sucked in through your front grille and pulled out of the reverse vent. the air rushing over the vent pulls hot air out of the radiator or engine depending on placement. air goes front to back on a radiator if air was being pulled in it would create stagnant air because assuming you car is moving in a forward direction air will always be moving front to back.
 

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Discussion Starter #3
Thats precisley what I said to my friend, he said, don't think of air as moving, think of it as a liquid with no direction. It makes sense both ways(it drawing air out, or in)...
Also would explain why some hoods don't cool properly, or at all (air being drawn in and like you said, creating a high pressure zone behind the radiator, hindering flow by the fans/forward movement of car). Hmmm, any other inputs?
 

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Dont forget about removing or venting the underbody panels so you sort of creat a venturi effect... cold air up from the underside of the car out the top.. whereas before it had no way to convect out the top of the engine. I have the vis Invader, on my o1 boosted is before i installed it underhood temps were really bad 400 degree temps.. with the hood it dropped to around 320 or so.. so it does work...
 

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does your friend know we have a front grille and air dam that allows air to flow into the engine bay?
 

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Discussion Starter #6
yeah, just he was pointing out the fact that air inside the engine bay would be less pressure than air directly infront of the bumper, grill, windsheild etc. and would mean air would rather flow INTO the bay than out of. Logically, it seems like reverse vented hood would just allow air to pass through. And that it would create a vaccum to suck air out through the top. Thanks for the info on the VIS invader, 80degree drop is nice.
 

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The air moving over the hood creates a lower pressure area than the air in your engine bay. Moving air always creates a lower pressure area, and pressure drops the faster air is moving... It's what makes planes fly by forcing air to move quicker on the top side of the wing than underneath.

Air is forced into the engine bay by the grille and bumper openings, since air directly in front of them has nowhere else to go.

Air is pulled OUT of the engine bay by the lower pressure over the hood making the higher pressure air in the engine bay come out of the openings. (this works on rear-facing openings and vents, front-facing openings are working the same as your grille and bumper openings... FORCING air into the engine bay)

If a hood vent is improperly designed, it can cause both push and pull at the same time, with reduced effects on either or even negative effects.
 

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Your friend had it backwards. Pressure is inersely proportional to velocity. The moving air over the hood causes a low pressure situatioin relative to inside the engine bay. The high pressure inside the engine bay will push air out of the hood vent (if its not a scoop-type vent, of course) Tell him to look up bernoulli's principle.

It's the same thing when you roll down your window at high speed and your ears pop. The fast moving air past the window causes a low pressure situation, and the relatively high pressure inside the passenger compartment pushes air out.

Other factors include heat (pressure increases with heat), and air intake (theres a ton of air being fed into the engine bay via the grills.)
 

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physics 101 :lol:
 
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