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Old 12-29-2008, 09:16 PM   #1
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Default NACA duct on bumper for CAI?

I saw this thread on CR.net: ClubRoadster.net • View topic - NACA Front Bumper [ Guest ] while looking for info on doing a NACA duct on the headlight lid. Seems like a good/better idea. I wonder though if a NACA duct is really the best kind of duct for a front bumper. It seems to me (please correct me if I'm wrong) that the benefit of a NACA duct is when it can replace a hood scoop or some other kind of protruding scoop that would mess up the aerodynamics of air flowing around the sides, top, or bottom of a car/plane. With the air smashing into the front of a miata head on it seems kind of useless in that respect.

I do think its an interesting concept and I might do something like it. So do you think a regular brake duct like this: Howe Racing RE206 - Howe Air Ducts - summitracing.com would be better at funneling air to an air filter behind it or is the NACA duct really the best way to go?
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Old 12-29-2008, 10:01 PM   #2
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Though I'm not trained (educated) in Aerodynamic Theory, other than aestetics, I don't see the benefit of a NACA on the front bumper at sub-100mph speeds. A flush opening should draw enough flow to meet most needs.

And as an associated aside, when we were gauging the size hole need for my oil cooler, Corky spoke of a, "1/8th rule of thumb", meaning your duct opening should be one eigth the area of the heat exchanger you are feeding. (Though I don't know how this would apply to CAI...)

For the earlier mentioned century-plus speeds, I would want the smallest opening possible to allow more air to flow around/over the car vice into the engine bay and thereby under the car.

- L
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Old 12-29-2008, 11:00 PM   #3
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Quote:
Originally Posted by l_bader View Post
And as an associated aside, when we were gauging the size hole need for my oil cooler, Corky spoke of a, "1/8th rule of thumb", meaning your duct opening should be one eigth the area of the heat exchanger you are feeding. (Though I don't know how this would apply to CAI...)


Thank you sooooo much for this info. Now I can relax and buy the carbontrix kidneys.
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Old 12-29-2008, 11:04 PM   #4
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whoa, that BRG is my twin. We even have the same hood.
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Old 12-30-2008, 01:09 AM   #5
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NACA ducts are awesome if they're installed correctly, so IMO that BRG = not awesome. NACAs aren't meant to be facing the wind like that, they're supposed to draw air in as it flows over a surface. Those are also humongous, they'd be borderline overkill on a race car so they're ridiculous on that BRG.
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Old 12-30-2008, 11:33 AM   #6
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cool, thanks for confirming my suspicions.
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Old 12-30-2008, 01:06 PM   #7
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Quote:
Originally Posted by kotomile View Post
NACA ducts are awesome if they're installed correctly, so IMO that BRG = not awesome. NACAs aren't meant to be facing the wind like that, they're supposed to draw air in as it flows over a surface. Those are also humongous, they'd be borderline overkill on a race car so they're ridiculous on that BRG.



+1


Though they'd likely still work, mounting them like that probably defeats the purpose of using a NACA style duct. Standard square brake ducts are likely just as effective.
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