Fog Light Brake Ducts

DrumrBoy

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I've always heard that too... "don't even bother trying to use the fog lamp holes for brake ducting". Does anyone know why its a low pressure area WITH a brake duct hose in place?

I can see that if there's a hole where the fog lamp used to be and nothing is done to contain inward airflow from escaping sideways once it hits the radiator.....THAT would tend to make air want to come forward out of the fog lamp hole....but if there's a brake duct/hose attached to the opening, it seems air can't come out that opening unless it enters by the brake rotor.

Does anyone know what causes the negative pressure zone there?
 

Dom426h

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Drumr,

What i think is happening is that the curvature/angle of the fascia is such that the air contacting the area between the crosshairgrille & foglight(very high pressure area) is deflected Over/Across the foglight hole opening towards the side of the car. This air creates a "forcefield" that blocks the air traveling directly perpendicular to the foglight opening that one would logically think could just go right on in and cool the brakes.

This effect changes as speed changes.

Here is a thread with some findings from roeracing:
http://forums.viperclub.org/threads/606797-Sean-s-facia-pressure-data

Some good info here on an effective DIY Viper brake duct kit:
http://forums.viperclub.org/threads...ct-Cooling-Installation?p=2992784#post2992784
 

DrumrBoy

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Thanks Dom, I missed that one in 2007. Good info though and hypothesis on why its happening.....not so much direction-of-car pressure as flow across the opening sucking air out.

My ducts are fed from a custom fabbed scoop under the fascia. Works great but makes the car one inch more likely to scrape. I was just interested in the logic behind the long-standing "truism".

Also the 105 mph thing makes it almost moot. You generally need brake cooling after slowing down, so most often you'll be going way less than 105 when you need the airflow. An exception is two big straights separated by a hairpin but that's not too common.

Thx for posting that old thread!
 

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