I'd jump on a duct like that GM one.

Interesting that the photo seems to show one outlet is oval, other circular.

 

We're too busy with other projects just now to design a printable duct for the NA/NB. Maybe someone here can do it an upload it to one of the CAD sharing sites.

- L/R handed
- Sized for standard 3" ID duct hose from aircraft spruce
- sections printable in a typical Bambu X1 sized bed
- Ideally wheel end goes all the way to the caliper and full steering lock so gap when straight ahead is short as possible

my .02

 

I've got a pair of these sitting in my garage. Photo's a little deceiving. Both outlets are circular.

 

Along with Emilio's design thoughts, it would be great if there was an easy way to attach it. On the NB (at least) there are a couple places towards that front that you can use, towards the subframe we may need to drill a hole and put in a rivenut or something to attach it.

Unfortunately, just like @OptionXIII it's out of my skill set to design it in CAD, but I'm more than happy to print it up and test it. (willing to print it up for whoever designs it too, if they don't have a 3D printer.)

 

Quoted for truth, and also coming soon by yours truly (through DCBE). We also have sold a handful of 3" fog light intakes already. Not sure why everyone else limits these to 2.5", since there is space for them to be 3"...

 

Here's my... pretty half baked solutions I've been working on. Testing a few different things. I track my car a lot and eventually want to run ducts from the stock foglight cutouts in my nb1 bumper as I don't plan to do an airdam. I have made some prototypes and test fitted them, they looked awesome but have not been track tested as I haven't dealt with the hassle of getting 3" ducts properly run to my bx11 kit.

For now I have a "scoop" style duct mounted to the supermiata brake ducts, the flared opening is about 3.5"

nb1 duct adapters for 3"

nb1 duct adapters for 3"

nb1 duct adapters for 3"

Supermiata "scoop" style ducts

Supermiata "scoop" style ducts

 

Those are cool, I'd love to see them routed to some sort of NACA duct on the bottom of a splitter, although Miatas aren't typically limited on space in the front for big ducts like that, as you found.

 

So those are cool as heck. I was told by FM that the reason why fog light hole brake ducts don't work well is the airflow likes to hit the front bumper and then fly 'passed' those inlets. I had though about including a forward projecting 'catch' if that makes sense on the outside edge of somethiung like what you've done, I just never actualy bought a 3D printer to try it out. If I can describe it, essenitaly would be a vertical project from the outside edge of the fog light forward that would catch the air rushing sideways across the bumper. Not sure if that works at all, but it did in my head.

My incredibly crude drawing:

 

FM is right to some extent. Further you get from the centerline of the of the car, the more the air is moving sideways across the nose. That's why end plates on splitters work so well. We have built several cars with our brake duct intake inside of radiator ducting. It's a better high pressure area.

It's important to stay focused on pressure differentials and not necessarily the presumed direction of airflow.

 

At one time I owned and tracked a 981 GT4. The brakes, even with OEM pads, were indefatigable - partly because the were massive but also because they featured formed brake scoops (similar to those posted by curly above). I always thought they would be a good idea on any Miata but I guess it required cheap 3D printers to make them a reality. A local Miata Club member printed these up for me this summer:






Easy installation with some double-sided tape and a metric ****-ton of zip ties. Only one track day with them, so far, but the brakes remained fade-free and the pedal as firm as it gets with an ND. They also remained intact and in place after I mowed the grass one lap.

Here's the link if anyone wants to try a set for themselves:
https://www.thingiverse.com/thing:5591605

 

I did some A/B testing with the singular ducts i have by taping up one of the ducts and repeatedly nuking the brakes from 60 to 10 on a dead end road for about 10 minutes, then taking a long slow cruise to get them cooled off. I couldn't find any real obvious differences in brake temperature with my infrared gun aimed at several different areas of the brakes. I'm not confident in my testing methodology, but would loove to see you try to do the same thing with your ducts. Those couldn't be simpler!

 

Really love the idea of those deflectors just for simplicity/packaging over ducts. I'm having trouble telling from the pictures, though, are those pointed at/able to deliver air to the hub center and not just the inner rotor face?

Was thinking of doing something similar on my car using GT3 deflectors but need to take a closer look at the knuckle/hub packaging to see if I can direct air to the center of the hub. I've heard stories of guys running ducts/etc. to the inner rotor face only and cracking rotors.

Building bargain brake ducts from Porsche GT3 parts | Articles | Grassroots Motorsports

 

They don't point at the hub center but at about the level of the ball joint, with some airflow likely going to the rotor face and some to the hat. I don't think it's really feasible for a printed design to feed air exclusively to the hub center.

 

It's not very detailed information, but I'll cross-post from my build thread to share my experience with the ducts I threw together using perhaps 3/4 of my ***. Better than half-assed, but not optimal.

I'm running G-Loc R12 compound in BX11 brakes on a K24 Miata. Last season I went through pads much faster than I expected and the inside/outside pads wore at different rates. I've never had an issue with these pads overheating or fading, the only issue has been consumption.

These are the inlets and ducts I built. The driver's side duct is slightly blocked by the lip on the radiator inlet in the stock nose. Pretty basic - inlets next to the radiator duct inlet, there's no sealing around the stock bumper inlet, but all the frontal area is blocked off. Ducts are CAT-12 ducting, 3" ID from Aircraft Spruce (their part number: 05-29812-8). I bought eight feet and have about a foot left over. They terminate in the BX11 duct mounts. I have a zip-tie chain that holds them up and inward just in front of the sway bar mount. They're suspended from a disused M6 threaded hole (probably for the stock splash pan) and then drawn inwards by a zip tie connected to the bottom of the radiator bracket.


The other side is nearly identical, but has the inlet moved up due since there's no tow strap/hook in the way.



When new, the R11 pads consistently measured 12.2mm in thickness, including the backing plate.

After one weekend at Sonoma (5.6 hours, per my engine hour meter, which includes paddock time), they measure 11.2-11.4mm (average 11.28mm). Let's call that 11.3mm, for a pad consumption of 0.9mm.

Last summer, I measured amount of pad consumed at a single Sonoma weekend as being between 1.2-1.8mm. I don't have measurements for each individual pad, or for how much driving I did that weekend.

I'm almost more impressed by the consistency across the pads than anything else. I'll also note that while the paint color of the pads has faded a bit, they are still visibly blue. I don't recall the previous pads retaining their color past the first use.



I'm happy enough with these results that I'm not going to optimize the ducting any further at this time. I've got other problems to tackle. Hopefully this shows that for a reasonable amount of investment (time and money), you can gain some improvements in pad life.