NACA brake cooling duct project

[GJarrett]

I've been reading several brake cooling duct project threads here and noted the various duct routing issues along with the DIY requirements of cutting out grill openings etc (I prefer keeping my fog lamp/running lights). I think I may have figured out a simpler solution and will be ordering parts soon to give it a try.

I used to be a member of EAA (Experimental Aircraft Association), have built and flown a kit plane, and have just enough rudimentary knowledge of airflow to get me in trouble LOL. NACA inlets / scoops are a proven design from long ago that have stood the test of time to draw and direct airflow for cooling purposes. Also, the GT belly pan has small air valleys on it that look like they don't do much of anything but Ford claims they help cool the brakes, so herewith my idea - improve the belly pan to true functionality with NACA scoop inlets.

I plan to install a couple of NACA scoops onto the rear of my belly pan right in front of the wheels and directly route a short section of hose from the scoops to a set of FTB brake cooling plates. That will involve a simple cutting of holes into the belly pan instead of removal and modification of the front bumper and grill and also take out half of the hose routing and access issues. Parts needed:

FTB brake cooling ducts

NACA scoops ; something like this:

https://www.pegasusautoracing.com/productselection.asp?Product=3627

hose

3" to 2.5" turbo reducer coupler to mate the 2.5" outlet of the NACA scoop to the 3" size of the FTB duct plates.

https://www.amazon.com/Squirrelly-Silicone-Reducer-Coupler-T-Bolt/dp/B0778Y4KJT

The belly pan would look something like this, except the scoops would be farther back on the Mustang's.

Any thoughts before I order parts? I am missing something or not thinking something through, or do y'all think this will work?

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[1 old racer]

just keep us posted on this project. I am very interested in how this turns out

 

[GJarrett]

Will do. I will be at VIR next month and hope to finish the project before then. Not quite sure how to judge effectiveness aside from shooting the rotors with a heat sensor after the last run of the day and see the temps. I cooked my brakes at AMP last time and could smell them. I've upgraded to Steeda two-piece rotors and EBC track pads now. I'm just a novice with an EcoBoost so I figure this ought to be all I need. The VIR sessions will be 30 minutes not 20 minutes and I want to be able to run the whole half hour without bailing out early like I had to at AMP when my brakes started smoking late during a 25 minute session at the end of the day.

 

[mikeD4V]

Also, the GT belly pan has small air valleys on it that look like they don't do much of anything but Ford claims they help cool the brakes, so herewith my idea - improve the belly pan to true functionality with NACA scoop inlets.

The GT performance pack (GTPP) belly pan has air channels to send air toward air deflectors on the GTPP control arms which direct air toward the brakes. The parts work in conjunction with each other so you'll need the GTPP control arms to get max benefit from the air channels. The gt350 belly pan also them and air channels for the transmission.

 

[cop on my back]

The GT performance pack (GTPP) belly pan has air channels to send air toward air deflectors on the GTPP control arms which direct air toward the brakes. The parts work in conjunction with each other so you'll need the GTPP control arms to get max benefit from the air channels. The gt350 belly pan also them and air channels for the transmission.

He is running hoses from the ducts to a set of plates at the brake hubs, no need for the PP lower control arms. That factory set up on the PP car is a bit of a farce in my mind, I think the benefit is minimal at best when all they are doing is deflecting air in the general direction of the rotor hub.

 

[mikeD4V]

He is running hoses from the ducts to a set of plates at the brake hubs, no need for the PP lower control arms. That factory set up on the PP car is a bit of a farce in my mind, I think the benefit is minimal at best when all they are doing is deflecting air in the general direction of the rotor hub.

Just clarifying that the Ford design actually has a function and how it's designed to work. There are a few companies offering larger control arm deflectors instead of ducts and plates. FWIW, I'm running DIY ducts from the front grille to backing plates instead of PP control arms.

 

[ddozier]

There is a lot of interesting stuff on NACA ducts and how to get the most airflow through the duct in a forum i found a few years back. I have this saved in my bookmarks as I often refer back to it.
http://www.landracing.com/forum/index.php?topic=9912.165

The gist of it is NACA ducts are not able to move as much air as a forward facing duct, mainly because they are designed to allow air to move over the duct and create the least amount of drag at the expense of overall airflow. Most of the testing and design work for NACA ducts are for airplane use and are not really that effective at car speeds. Yes they will move some air but brake cooling requires a lot of air movement and air velocity to allow it to travel through a duct and then through the vane system of the rotor. NACA ducts require a flat area with enough surface area in front of the duct to allow a boundary area to form. They do not work well in turbulent air because they take air from the boundary layer and create vorticies to roll the air into the duct itself, with turbulent air around the duct the vorticies may not form and the duct is just a hole in the body work at that point. If you can not generate enough airflow to overcome the restriction at the rotor the air will stack up in the duct hose and eventually the duct opening, then it will stall and becoming useless.

If you do a downward facing NACA duct under the front belly pan I think you will likely need a scoop on the trailing edge of the NACA duct to force the air into the duct to achieve your cooling needs. Others have made ducts that pickup air from the front fascia without removing the driving lights, I would look into that method first and see if you can find a solution that would meet you needs.

I could be wrong but this is my understanding of how these NACA ducts function.

Dave

 

[GJarrett]

You've given a lot of food for thought; I did read the extensive post you linked to and noted that the author stated that NACA ducts are not optimal in acclerating/decelerating situations. I've already ordered the parts so we'll see how it goes; the ducts weren't that expensive so either way I've got nothing to lose by trying. I do think the airflow under the belly pan is probably more laminar than turbulent or the Ford engineers would not have designed the GTPP belly pan channels to draw air up to the control arm air deflectors. My thought is if a simple channel works a little then a NACA duct ought to do a whole lot better. If not, I haven't lost much and we all learn something in the process... then I'll still have the FTB brackets and hose and can route to a front duct like everyone else if it does not work.

I don't expect the NACA ducts to have anywhere near the effectiveness of front facing inlet taking in ram air; however I'm just a novice/intermediate with an EcoBoost and won't be running it as nearly hard as most of the rest of you experienced track guys with GTs and GT350s. Next weekend I'll install my new Steeda two-piece rotors, EBC track pads, and the ducts; then see what happens at VIR in a couple of weeks. I am thinking of covering one of the ducts for my first morning session and as soon as the session finishes I'll take a reading with a temp gun on both rotors and see if the open duct made much difference.

 

[ihasnostang]

hopefully this works, would be nice if you could get some airspeed data. i thought i recall seeing some naca ducts on the underbody of the ford gt last year when they had the back wheels on race ramps. i would also assume they are more effective when they are on a curved surface so that the duct isnt parallel with the airflow ( as you have on your under tray)

 

[ddozier]

hopefully this works, would be nice if you could get some airspeed data. i thought i recall seeing some naca ducts on the underbody of the ford gt last year when they had the back wheels on race ramps. i would also assume they are more effective when they are on a curved surface so that the duct isnt parallel with the airflow ( as you have on your under tray)

My understanding is a NACA duct is less effective on a curved surface than a flat surface. They also require a flat non-curved surface before the start of the inlet to allow the air to attach itself to the panel without any turbulent air before it reached the leading edge of the duct. Without a lot of testing and measuring at many different speeds it is hard to say if the placement of any NACA duct will work, any of the surfaces in front of the duct could create unstable airflow before it reached the duct and the NACA duct will not be able to draw in any air as intended.

Dave

 

[GJarrett]

Project completed. Note the channels in front of the inlets that will cause turbulence; I did a quick and simple short term fix by adhering high strength duct tape in front of the inlets to cover the channels and hopefully work well enough to provide laminar airflow to the inlets.

I plan to cover one of the inlets with tape on the first morning run at VIR, then take readings of both front rotors and calipers with a temp gun as soon as the session is over to compare temps between the functional inlet and the closed one . Hopefully it will indicate a decent effectiveness. We'll see.

 

[1 old racer]

Thanks for this DIY

 

[GJarrett]

Well I've got results in, sort of. I did an early morning run in cooler weather at 9:30am and I'm a novice who has never been on VIR before, so ambient temps were low and I also did not drive hard while trying to learn lines, etc. After the cool down lap and parking in the paddock, the open duct front rotor read 215 degrees, the closed duct was a solid 250+ degrees, about 15% cooler with the NACA duct. I haven't found anything in another thread about someone else that did a similar test by blocking one fog lamp opening on a rotor duct, so not sure if this is significant or not. My last session of the day run harder in hotter weather with both ducts open, the rotors were reading 250-260 degrees after the cool down lap; I assume they would have been over 300+ without them, so for the effort I am satisfied.

I do believe all of these temps are way below my last event when I could could easily smell my brakes and started losing pedal pressure, so I also have to give credit to Steeda for their two-piece rotors that they claim to run up to 200 degrees cooler. With this setup, even after I get better/faster I can't imagine my brakes getting anywhere near the boiling point of a good brake fluid like Motul 600/660 or Castrol SRF.

For an Ecoboost that will never be able to hit the higher speeds and braking needs of a GT or GT350, I think I can quit worrying about my brakes now and call it good.

 

[1 old racer]

Thanks and very good info

 

[GJarrett]

Follow up report; I was running much harder/faster my second day. Rotor temps stayed in the low 300 degree range. If some of you with GTs / GT350s wanted to follow up on this idea, I would think that installing inline blowers on the duct lines would make up for any deficiency of the NACA duct setup.

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