The Brake Duct Thread
 

Figured we needed a dedicated thread where we can dump our pics, ideas, solutions, sources

NA/NB, NC or ND?
Duct hoses or deflectors?

This is from a build we did in 2018. 3" hose on and old TSE kit. Those rotors look so tiny now..
https://cimg1.ibsrv.net/gimg/www.mia...9ee852e379.jpg

Just the basic "Supermiata" forumula here...

NA with ply splitter/poly airdam and Singular backplates. 3" ducting. I ziptied mine to the splitter brackets and sway bar for support. I ran the zipties through vinyl tubing to protect the ducting material. It's held up pretty well for going on 6 years.

https://live.staticflickr.com/65535/...06dcfd26_c.jpg

https://live.staticflickr.com/65535/...360de17d_c.jpg
https://live.staticflickr.com/65535/...5889728d_c.jpg
https://live.staticflickr.com/65535/...9d408d94_c.jpg

My Miata has become an occasional-use track car now that I drive my E46 most of the time. This setup worked well before I trubo'd it. I used horizontal zip ties to create mounts on the sides of the undertray, then zip tied the ducts through the mounts. These are 2.5" ducts with Singular attachments. Ducts originate at the fog light holes. Tires are 225s on 15x9" rims.

How it was done 10 years ago...
https://cimg6.ibsrv.net/gimg/www.mia...a6fca5f908.jpg


https://cimg7.ibsrv.net/gimg/www.mia...28e1a43100.jpg


How it looks today...

https://cimg8.ibsrv.net/gimg/www.mia...699a8df70e.jpg

That was fine for 130HP. Now I am boosted to 6psi and 180HP, and I would call the setup just adequate for occasional track days and nowhere near enough for serious track work.

This is how mine came out. I kept bends to a minimum but definitely need to upsize them to 3" (and supermiata ducts to go with the BBK). That said, these brakes have been endless for me so it's not way up on my list.

https://cimg6.ibsrv.net/gimg/www.mia...3d25d76a6e.png

This thread is relevant to me as I have the SM BX11 ducts/shields on the front, with nothing connected to them (NA chassis). I have the recommended ducting from Aircraft Spruce sitting in a box in my dining room. But I’m overthinking things, because that’s what I do.

I’m NA, so no turbo hoses to worry about.

I’ve sat and looked at things and am wondering whether it’s possible (or worth it) to run 3” aluminum intake tubing in as long of a straight run as possible from the nose, underneath the chassis rail. Smooth bore aluminum tubing being, in my mind, better for airflow than even good soft tubing.

is my imagination failing me at seeing how the suspension and wheel movement would prevent this hard tube from running below the sway bar mount, hard against the subframe, between the arms?

The last mile of that aluminum tubing needs to bend, so you'll have to finish it off with something. As you turn the steering wheel the angle of the plate changes.

That would work, but I did not find it to be necessary for the 100+ track hours I put on my car before switching horses.

I ran 2.5" tubing to sport brakes with the inlets scavenging from the positive pressure in front of the radiator and never had heat problems. Normally aspirated cars have excess water cooling capacity and don't mind losing a little air to the brake ducts.

FI is a different story altogether, as heat rises significantly absolutely everywhere and must be dealt with appropriately. Hence why my inlets are now at the fog light holes (NB2), and I call my brake cooling situation just adequate for occasional track use. I really need a BBK and 3" ducts now with 180HP.

Yeah, I'm at 200rwhp and the BX11s are holding up without ducts, though pad wear is maybe a bit high. I think I'm fixated on a SuperMiata statement somewhere that 3" was just barely flowing enough, but anything larger was not physically possible. So before I even put the basic solution on, I'm trying to optimize it by increasing the flow using aluminum tubing for the straight shot (I didn't think it was necessary to acknowledge that flexible tubing is a requirement at the wheels). I haven't seen anyone do this, so I'm wondering why not. I'm guessing that as you point out, the gains aren't worth it.

One other amusing thought - since we're talking about 3" ducts here, there are plenty of 3" tubes for MAF sensors for muscle cars, ie: https://vortex-performance.com/produ...sing-maf-tube/

It'd be amusing to see some data on just how much air is flowing through our ducts...

Following this with interest. There don't seem to be any good off-the-shelf solutions for the NC. AWR makes backing plates for the 11.5" NC and larger 12.7" RX8 rotors, but they're 2.5" inlets and blast all the air at the inner rotor face and nothing towards the hub. I have a set of said plates and am going to mock them up and see if there's room to chop off the 2.5" inlets and replace them with some 3" inlets that point towards the hubs.

https://cimg7.ibsrv.net/gimg/www.mia...d40645f27d.png

We have some ducts in Laz we haven't even hooked up yet, however this peaked my interest when I saw it, he's been making them for a bunch of the west coast Lucky Dog Miata teams.

Here's the source: https://britainracing.com/products/n...ta-brake-ducts

https://cimg5.ibsrv.net/gimg/www.mia...9073a61c44.png

There's plenty of OE brake duct solutions that don't involve hoses, my favorite being the Porsches. The amount of work they must have put in to the computer models to capture the air with essentially only half the duct is impressive.

https://cimg3.ibsrv.net/gimg/www.mia...e82881e678.png

Biggest issue I see is people installing brake ducts expecting them to last 5 years of track days. We'd replace at least the rear brake ducts that scrape on the ground once a weekend. Front hoses, unless you put rack limiters on that are properly sized, are trashed after a race weekend if you turn too much.

The 86 and ND both have basically no room for a proper 3 inch brake duct. So we're using deflectors, which we have had very good luck with.

On the NA/NB, we really think that big fat hose needs to be inside of the frame rail. Trying to run it underneath the frame rail is inevitably going to get it tangled up in the wheel and torn open. But running it inside the rails is not easy to do. Takes some creativity and sometimes moving other important things around.

I have seen some high-end production bodied race cars with big NACA ducts on the hood feeding hoses that went straight down through the engine bay and out to the wheel. That can be a good solution if you're willing to hack up things.

https://cimg7.ibsrv.net/gimg/www.mia...6edc9dbd0a.jpg

Could there be an idea of a fender entrance strategy with the naca duct on the NB/NA. If you could align the entrance with the shock, you could come vertically down and into the brake with little to no chance of tire issues.

When I originally had my ducts installed, i blocked one off and did some aggressive braking then attempted to detect any difference possible in the heat in any areas around the rotor. I hate to say the temperatures with my infrared gun were within 10 to 20F in all areas on both sides. This was 3" ducts from the fog lights run along the frame rail and a fairly hard turn in to stay out of the way of the wheels.


I found some steering angle limiters for cheap so I'm going to install them and see where that leaves me. I dont have a dedicated track car, but I also dont need to be able to pull a u turn inside of a single lane. I have a feeling this will open up some angles for the ducting big time. Here's a video on in the install for future peeps:


and where I'm buying them from:

https://slrspeed.com/products/miata-...FF5rcckaKwFwSb

Now you have my brain going. This may be a dangerous thing. I hope my tone in the many cases where I've quoted you and asked questions has come across as a nerd who is trying to learn by asking questions others won't, rather than as some prick who thinks he knows better questioning people who actually know what they're talking about. I'm honestly trying to learn from the best, without having to go back to college.

I see this idea as having a couple of sub-ideas:

1. Feeding air in from NACA duct in an area of smooth airflow
2. A different path from the duct inlet to the outlet

I then start to think about which limitations the design is overcoming:

1. Pressure differential between the inlet and outlet of the duct
2. Restriction within the duct due to:
   1. Length
   2. Cross-sectional area
   3. Laminar flow (I don't have the right vocabulary - I'm trying to encompass things like corners in a rectangular tube and the smoothness/material of the sidewalls)

To compare the approaches, I'd look at a 3" duct from the hood to the brakes and a 3" duct from the nose to the brakes. There's not really many areas in my NA engine bay, either with the BP or the K24, where I think I could feed a 3" brake duct hose from the hood to the area behind the front wheels. So let's change the variable of cross-sectional area and leave the others alone for now. How much better would the hood-to-wheel-face pressure differential have to be to overcome that change?

God, I feel like some modeling software, or maybe a class in fluid dynamics or something would really help me here.

But ballpark, in the infinite wisdom of the humans and AI who read this thread, what's the big advantage to the hood inlet strategy over the nose inlet one? And is it enough to make such an approach even theoretically possible in the tight engine bay of a Miata?

I think packaging mainly. Air mass will slow down a bit when forced to change direction but what really drives air mass to go from one place to another is pressure differential. A lot of newer cars like the 86 and ND, have virtually no space outside the frame rails for 3" ducts and are too tightly packaged to fit them inside the rails. Look at so many Euro and Japanese cars that use deflectors instead of ducts. The only access remaining is up top. On a race car with everything in the nose gutted out, you gain enough packaging space to route tour straight-ish shot hoses from the nose. But with most/all of the OEM stuff still in the nose, one might have fewer options and that's where a top inlet might make sense.

On Huevo, our TT ND2, we have moved or deleted some of the OEM stuff from the nose. But most of it remains so there wasn't room for a 3" a duct solution. So we're using deflectors, which we're still developing. Another reason we opted for deflectors is that even if we cam up with a duct solution for our build with some stuff stripped out, almost no ND owners out there would be able to replicate that solution. For us, a primary driver on Huevo is finding solutions we can either share for free or useful parts we can offer.

I have a removable splitter and front bumper so I can easily get the car on my trailer. I needed a way to quick disconnect the brake hoses. I found these plastic RV sewage connectors for 3” hose and they work great. They need about an eighth of a turn to connect. I did remove the rubber o-ring so they were easier to twist on and off, but these work great. (They were also cheaper than the metal flange everyone seems to buy to connect using a normal hose clamp.)

https://cimg1.ibsrv.net/gimg/www.mia...b399b5f9c6.jpg
https://cimg4.ibsrv.net/gimg/www.mia...bfc730513d.jpg

I also 3d printed up some brackets to help hold the hose in place at the front of the car (using HVAC zip ties to hold it onto the sway bar and on my subframe up where the upper control arm attaches)
https://cimg3.ibsrv.net/gimg/www.mia...f51ba3cb06.jpg

Not the best picture, but you can see them holding up the hose here. As far as hose routing, I did the same as what Emilio showed on his earlier. I haven't had any real issues with rubbing.
https://cimg7.ibsrv.net/gimg/www.mia...310b0d6535.jpg

I've also been thinking about running a tube the straight shot back and then a smaller piece of hose to connect to the wheel. I was thinking about repurposing a shop vac "wand" but they are only 2.5" in diameter. Will be paying attention to this thread in hopes that someone comes up with a good idea.

With 3d printing becoming so ubiquitous, I'm surprised I don't see more people using hard piping for a larger portion of the brake ducting. Other than the very tidy NB2 fog light brake duct inlet (only 2.5" unfortunately), I don't see much out there on Miatas. A variable cross section duct to fit a narrower gap with a smooth interior has got to flow better than the usual orange silicone flex tubing for minor bends. The narrower, taller duct shape would let you sneak the same amount of airflow through a path a round 3" hose might not fit, or fit well.

The C6 Corvette brake ducts, or even the NA Miata "Cobra" over the radiator intakes are great examples of what I mean. Some similar hard ducts to get air past the front tire's movement envelope, transitioning to flex hose to get it to the hub center, would be a pretty slick setup.

https://cimg8.ibsrv.net/gimg/www.mia...9711974b01.jpg https://cimg9.ibsrv.net/gimg/www.mia...d3f40543e1.png

That sort of smooth, 3d modelling is outside of my skillset unfortunately. I assume that's true for most people.

Agreed. That variable cross section duct can flow enough air and squeeze under the frame rail without getting whacked by the wheel/tire. The ND and to a lesser degree, the NC still don't have a good path from the nose but the NA/NB could benefit from a 3D enclosed duct shape.

Some really cool ideas here. Love that RV hose connection idea!