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NACA Duct measurement request

 
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Qik Nip  



Joined: 16 Jan 2015
Posts: 122
Location: Kentucky

PostPosted: Fri Oct 05, 2018 1:07 am    Post subject: NACA Duct measurement request Reply with quote

Can anyone here with a 924 Turbo sitting in their garage do me the favor of measuring the width, depth and length of the NACA vent in the hood? I'm considering "grafting" one on the driver's side hood of my land speed (naturally aspirated) 924. Thanks
Rick
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Fri Oct 05, 2018 4:23 am    Post subject: Reply with quote

Can check mine when I get home, if no-one beats me to it...
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Vaughan Scott
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Joined: 16 Jan 2015
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Location: Kentucky

PostPosted: Fri Oct 05, 2018 6:10 am    Post subject: Reply with quote

924RACR wrote:
Can check mine when I get home, if no-one beats me to it...


Thanks. So far you're it!
Rick
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CÚdric  



Joined: 27 Aug 2004
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PostPosted: Fri Oct 05, 2018 6:44 am    Post subject: Reply with quote

Im curious, why do you want it?
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Fri Oct 05, 2018 8:11 am    Post subject: Reply with quote

length 15", width 7", depth 1.5"... add maybe 1/2" all around for the "outside" dimensions for grafting on the hood. Maybe not super-precise, but should give you some idea of the general size...
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Vaughan Scott
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Joined: 16 Jan 2015
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Location: Kentucky

PostPosted: Fri Oct 05, 2018 10:13 am    Post subject: Reply with quote

CÚdric wrote:
Im curious, why do you want it?


Cedric:
I hope to get cooler air into the engine while avoiding the added air resistance created by a traditional hood scoop. The air under the hood of a fast moving car is subject to tremendous turbulence and I fear is resulting in each of the four carburetor throats receiving differing quality and quantities of air. I plan to plum the NACA vent into an air box enclosing all four of the Weber throats to both "quiet" it and deliver cooler (therefore more dense) air to the engine.
At least that's the plan!
Rick
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Joined: 16 Jan 2015
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Location: Kentucky

PostPosted: Fri Oct 05, 2018 10:14 am    Post subject: Reply with quote

924RACR wrote:
length 15", width 7", depth 1.5"... add maybe 1/2" all around for the "outside" dimensions for grafting on the hood. Maybe not super-precise, but should give you some idea of the general size...


Thanks Vaughn!
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gegge  



Joined: 27 Jul 2007
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PostPosted: Sat Oct 06, 2018 6:22 am    Post subject: Reply with quote

Remember that the hood is a low-pressure zone. Why not try connecting the carburator plenum directly to the batterybox? That is high pressure! Poor man┤s turbo
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MikeJinCO  



Joined: 08 Jun 2010
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Location: Maysville, Colorado

PostPosted: Sun Oct 07, 2018 6:35 am    Post subject: Reply with quote

Pegasus Racing has some NACA ducts that are meant to be fit into side windows, not sure about the size as far as airflow. I made a bucket to fit in the driver side headlight bucket somewhat similar to the fixed headlight conversion. Then I found an 3" tapered inlet inlet at summit racing. I haven't quit figured out how to install it neatly , yet, as it is not a refined part and I have the stock steel front panel. It probably would increase the drag. I still have the mold if interested.

I recall seeing your photo's and if you have the Dprod front end from CCP in Florida you might look at using the lower brake air duct if you haven't sealed it off.
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Sun Oct 07, 2018 11:21 pm    Post subject: Reply with quote

Agreed, ABS plastic NACA ducts can be cheaper; Pegasus is one of the more expensive places to buy. Try Hoerr Racing Products (HRPworld.com) or Summit or JEGS:
https://www.hrpworld.com/shop-by-category/brake-system/brake-and-aeroducting/bumper-ducting.html
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Joined: 16 Jan 2015
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Location: Kentucky

PostPosted: Mon Oct 08, 2018 6:51 am    Post subject: Reply with quote

gegge wrote:
Remember that the hood is a low-pressure zone. Why not try connecting the carburator plenum directly to the batterybox? That is high pressure! Poor man┤s turbo


Now that's interesting. To those wondering about his low pressure comment, NACA vents don't work well unless they are positioned in a high pressure area. That does however bring into question the use of the NACA on the turbo 931... Although a blower pulls air and perhaps therefore doesn't need a forced feed...
Anybody got the lowdown on that issue?
Rick
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poor-sche  



Joined: 06 Jan 2017
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PostPosted: Mon Oct 08, 2018 1:59 pm    Post subject: Reply with quote

The naca duct dumps air directly in front of the battery box and down onto the exhaust manifold. Its purpose is for cooling and looking cool.

The factory air box pulls air from the opposite corner of the engine bay (next to the drivers side head light).
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Carrera RSR  



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PostPosted: Mon Oct 08, 2018 7:28 pm    Post subject: Reply with quote

Not sure the that the NACA 'dumps' air.........remember air also flows under the car. My understanding is air is being drawn out of the back of the engine tray and under the car. This draws air into the engine bay via the NACA (and nose vents in the turbo). This keeps the engine bay and more specially with the NACA, the exhaust side flowing with cooler air. The NACA adds to the engine bay air flow and does not 'scoop' air into the bay.
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gegge  



Joined: 27 Jul 2007
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PostPosted: Tue Oct 09, 2018 5:41 am    Post subject: Reply with quote

Since the NACA is situated right above the exhaust/turbo and hot air is rising, in addition to a low pressure zone...

A NACA duct is only working properly in high speed, that is MACH speed. The ram pressure or air flow volumes is poor compared to protruding scoops. The trade-off to drag I guess.

I belive NACA was a cool design feature in 70┤car design. The Countach, Espada, Montreal, Mustang and 931 to mention a few. And F40 of course, ten tears later.
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Fifty50Plus  



Joined: 28 Feb 2008
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Location: Washington DC area

PostPosted: Tue Oct 09, 2018 10:33 am    Post subject: Reply with quote

NACA ducts work very well on race cars to put air in the cockpit for driver cooling. Adding flexible tubing allows us to aim the air wherever we want.
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