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Removing the Rubber onthe back of the hood at the fire wall for cooling??

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Removing the Rubber onthe back of the hood at the fire wall for cooling??

Old 06-21-14, 02:39 PM
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Removing the Rubber onthe back of the hood at the fire wall for cooling??

Ok ,sorry for thevague description ,I'm talking about the rubber spongy thing that follows thecontour of the firewall between the hood and the car


Now I've seen People lift the back of the hood a couple cm for cooling

and i've read people saying that removing that rubber causes a low pressure inside the enginebay with air going in through the back

I had removed mine , or well I never put mine on haha So i'm curious if the low pressure thing is true? or if not having that there helps with cooling ? or if its just really insignificant
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Old 06-22-14, 12:04 PM
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Originally Posted by Tem120 View Post
Ok ,sorry for thevague description ,I'm talking about the rubber spongy thing that follows thecontour of the firewall between the hood and the car


Now I've seen People lift the back of the hood a couple cm for cooling

and i've read people saying that removing that rubber causes a low pressure inside the enginebay with air going in through the back

I had removed mine , or well I never put mine on haha So i'm curious if the low pressure thing is true? or if not having that there helps with cooling ? or if its just really insignificant
If you look at a pressure map of a car in motion, the base of the windscreen is a high pressure area (relative to ambient), which is why some might say that it will push air back under the hood. This is the way cowl induction worked on some of the old muscle cars.

The other part of the equation is that the underhood pressure is also high relative to ambient, so it comes down to which pressure is higher -- above the hood or under the hood. Most things that I've read tell me the underhood pressure is higher, so it should help evacuate air.

I removed mine, and I don't know for sure which way the air is flowing. If you tape some strips of paper to the trailing edge of the hood, it might tell you for sure. I'd do it with my car, but it's not running right now.

BTW - cowl induction worked because the intake zone was kept separate from the underhood air.
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Old 06-28-14, 04:54 AM
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We did this on our MS Protege racecar to aid in cooling, even stacked a few washers between the hood and hood hinge to give us a fraction more gap.
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Old 06-30-14, 08:20 AM
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Originally Posted by elwood View Post
If you look at a pressure map of a car in motion, the base of the windscreen is a high pressure area (relative to ambient), which is why some might say that it will push air back under the hood. This is the way cowl induction worked on some of the old muscle cars.

The other part of the equation is that the underhood pressure is also high relative to ambient, so it comes down to which pressure is higher -- above the hood or under the hood. Most things that I've read tell me the underhood pressure is higher, so it should help evacuate air.

I removed mine, and I don't know for sure which way the air is flowing. If you tape some strips of paper to the trailing edge of the hood, it might tell you for sure. I'd do it with my car, but it's not running right now.

BTW - cowl induction worked because the intake zone was kept separate from the underhood air.

thank you , My car isn't exactly running at the moment either , but I should get it back this week so seems like a fun little test to keep me entertained
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Old 06-30-14, 08:24 AM
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Originally Posted by RacerJason View Post
We did this on our MS Protege racecar to aid in cooling, even stacked a few washers between the hood and hood hinge to give us a fraction more gap.

yes I've seen exactly that on a few cars But at the same time there are those who are nay sayers on this ..

BUT! Like was stated above I think thats a good idea maybe I'll even record it using my pro go
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Old 06-30-14, 08:28 AM
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It will work . On my gen 1 race car with front hinged hood we use hood pins that have a 1 inch gap above hood where pins go in and as soon as you are moving above 60 mph the hood rises up 1 inch to touch the pins ,So there is more under hood pressure than on top
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Old 08-11-14, 11:55 AM
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^^ do you have an engine splash guard on your car? What happens if you have a full undertray panel.... it may lower under hood pressure,no?
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Old 08-11-14, 12:14 PM
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Originally Posted by WJM ROTARIES View Post
It will work . On my gen 1 race car with front hinged hood we use hood pins that have a 1 inch gap above hood where pins go in and as soon as you are moving above 60 mph the hood rises up 1 inch to touch the pins ,So there is more under hood pressure than on top
This is correct. When I propped up the rear of the hood on my 1st gen both oil and water temps went down by 10*F. And yes the hood lifts up a hair on its own at speed.. Also when it's rainy, the hot air from underhood defrosts the windshield very very nicely. Without the factory blower/defroster vents/system.
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Old 10-15-14, 03:44 PM
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Guys,
Let's be clear on the terms lift and push. Push would be the underhood pressure pushing the hood up. Lift is the negative pressure on top of the hood "lifting " the hood from the outer surface.
It's not rising from underhood pressure. The air going over the front bumper, and the curve of the hood is a basic airfoil. It's lifting from lower pressure, (higher speed), on top of the hood. It may build more cowl pressure than underhood. 10 * change either direction may be instrumentation error. Unless it's thermocoupled and data recorded, it's a guess.

GD
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