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NACA Duct Questions....For those of you with experience :)

Old 05-09-07, 07:41 PM
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NACA Duct Questions....For those of you with experience :)

I am interested in knowing just how much air a NACA Duct brings in? I know a lot of race cars use them but they are also going very fast. Just how much air does it draw in at speeds below 80mph? Thanks

Chris
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Old 05-09-07, 10:00 PM
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this is impossible to answer since the amount/velocity of air being brought through the duct is directly related to the amount/velocity over the actual duct as well as pressure on both sides of the duct...not to mention what size the duct is example; duct on the windshield vs on the rear window.
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Old 05-10-07, 07:41 AM
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Definately need alot more information to answer the question. Since you want airflow, consider doing something like this http://cgi.ebay.com/ebaymotors/NASCA...QQcmdZViewItem

I didn't get the air flow I wanted out of a NACA duct so I changed to a fan and different duct and problem solved.

The fan will get you 170CFM it claims...
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Old 05-10-07, 02:18 PM
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I was considering utilizing the airflow under the car to cool the brakes. By attatching naca ducts to a flat underpanel and running hoses from there. I'll make a drawing.

Chris
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Old 05-10-07, 02:27 PM
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Kinda like this. I know that a lot of people pipe ducting from the front bumper. Which is how I have mine now, but I was just shooting ideas. Figured I'd see what you thought.

chris
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Old 05-10-07, 03:55 PM
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i think your idea would work, but to answer the question you need to know the size of the ducts and hoses. how much airflow you NEED is important too (more the better?) and then you could take pressure readings in the ducting.

we were talking to the manager of the volvo touring car team a couple years ago, and they had turned a headlight into a duct for the intake, but then the also ran a hose down to the bumper. we asked why and he said that over 100mph, the headlight went from pressure to vacuum. so they added a second duct
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Old 05-10-07, 06:03 PM
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As far as pressure readings, I really don't have the equipment to do that. I would be a standard 3in hose oulet and generic duct similar to this.

http://cgi.ebay.com/ebaymotors/2-NAC...spagenameZWDVW


As for the the headlight duct, you mean a hole in the front where the headlight went? You're saying instead of air being forced into the area where the headlight was, it was being sucked out? Essentially starving the intake pipe?
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Old 05-10-07, 06:57 PM
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well its a good idea...if there is pressure under there. but the whole idea of race car aero is to keep air out from under the car. so its kinda a catch 22. ideally one would want to run a air dam or splitter on the front which will hinder the efficiency of that duct placement(how much depends on how efficient the airdam/splitter is). I reccomend placing the inlet of the duct as low on the bumper as possible and then building an airdam below it..this way you get maximum pressure @ the ducts inlet and you knock down the amount of air let under the car....If you cannot or are not allowed to run an airdam then by all means place the naca where you were thinking as it will help evacuate the air from under the car....and I would be willing to bet there is a fair amount of air there in the factory config.
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Old 05-10-07, 07:02 PM
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As for getting pressure readings....depending on your ecu/logger if you have extra inputs just config up a couple of 2-bar map sensors and do some strait line tests with the sensors hose in different spots.....resolution isn't the best but you will get the jist of whats going on where.
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Old 05-11-07, 09:28 AM
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The front undertray you have in your drawing is supposed to be a low pressure area that generates downforce on the nose of the car.

The inlet of a NACA duct needs to be in a High pressure area, not a low pressure area.

Flow is a function of pressure differential between the inlet and the outlet. I doubt you are going to have a decent positive pressure differential between your inlets and outlets; I think you have a bad idea. I worked in a wind tunnel from 1981 thru 1983.
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Old 05-11-07, 10:43 AM
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Originally Posted by DarkKnightFC View Post
As for the the headlight duct, you mean a hole in the front where the headlight went? You're saying instead of air being forced into the area where the headlight was, it was being sucked out? Essentially starving the intake pipe?
yes. over 100mph the hole in the front of the headlight went from positive to negative.
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Old 05-12-07, 11:43 AM
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Fair enough. Thanks for your input.

Chris
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Old 05-13-07, 11:14 AM
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Naca

Originally Posted by DarkKnightFC View Post
I am interested in knowing just how much air a NACA Duct brings in? I know a lot of race cars use them but they are also going very fast. Just how much air does it draw in at speeds below 80mph? Thanks

Chris
The advantage of a NACA duct is much lower drag for the airflow compared to other scoop type ducts. It works by creating a vortex at the edges. I should be placed in an area of smooth airflow and not in a negative pressure area. Attached is an Excel table and plot converted to .doc. You can scale this as needed.
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Old 05-13-07, 11:18 AM
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Naca

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NACA.doc (35.5 KB, 366 views)
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