Icedawg

Brake Ducts.
We all know why you need them, and for a long time the Singular Motorsport ducting plates have been the most available, though there are some others out now (eg SuperMiata).
But the Singular Motorsport ducts seem to have been designed for a big brake kit, and most of the air coming out shoots right by the stock brakes. See the GRM photo with 11.75 inch brakes versus my car with stock brakes. So some modification is indicated.




Also, the air does the job best if aimed into the centre of the brake rotor where it can be picked up and spun out through the vanes. I had a set of RX7 ducts that just fired it at the inner rotor surface, and another that directed air only into the vanes. Firing at the back surface alone did not work, with rotors splitting regularly, while directing into the vanes gave much longer life (3 weekends vs 1).



Running with a turbo at 8 psi I cooked my Hawk DTC60 pads, and had noticeable brake fade after a few 20 minute sessions. This was with the stock rotors, Singular Ducts and 3 inch hose from the front bumper fog light holes on a 2001.

So I bought some 4 inch HVAC flapper valve plates from Home Depot, cut them to block the region outside the rotor, and direct air towards the vanes. Two small holes and a pop rivet gun mounted them in an easily reversible fashion. A better directional shape could be made that was less blocking, but race day was pressing upon me, and my skills are limited anyhow.



Cooling was much better. No brake fade over a race weekend. But the stock brake rotors are still getting hot enough to wear the DTC60 out much faster than they did when it was a Spec Miata. So it seems I am going to have to go the big brake kit route after all.

Gee Emm

Good work!!

blackzx3_13

I did something similar to mine

Icedawg

Very nice, better directive flow than mine.

norcal

Just in time, I have my front end apart for hubs and was contemplating how effective the air blasting onto stock rotor faces really was. Thanks for the side quest.

tfbmiata

I notice you dont have your undertray on. When I had my ducts installed I had to cut my undertray to pieces. That screwed up my cooling so I had to put it back and remove the ducts. Did you get your ducts installed w/ the undertray still intact? If so, how?

AussieMSM

Just cut a hole and run the duct hose through the undertray wall. Keep it tight to minimise air flow loss.

Icedawg

Well, can't have it there while working on it!
I cut the stock undertray up to allow passage for the intercooler tubes, but it did not interfere with the brake duct tubing, which was tied to the sway bar. But cutting it really weakened it, and my second test and tune track day it ripped apart, and was ruined. So thanks for the opportunity to expound upon the next step!

I looked at the 9 lives racing splitter design, and made a sheet of 1/8 inch hardboard that models that shape, but does not extend past the bumper cover to become a splitter. (A splitter would cost me NASA aero points, so nice as it is to have, I did not make it into one.)
For the vertical barriers, I cut the verticals off of the ruined stock undertray and bolted them in place. Then I mounted small vertical side shields on the hardboard undertray to cover any space remaining that was missed by the cut-up stock verticals.

Here is a pic of one of the 3 cardboard mockups I made along the way.
Racers tape currently seals the front edge, but I want to re-install the small stock lip that installs on the bottom of the bumper, in front of this undertray, so tape will no longer be required. (Every time I take it off it takes a bit of bumper paint with it, and it comes off between every race weekend so far.)

Icedawg

Following up on above post, the ducting for the brakes is entirely outside of the undertray region in what I built. I tied the ducting to the sway bar, and kept it outside the tray.
My problem was with the Flyin Miata intercooler hosing, which is really in the way of the undertray and forced me to cut it up and weaken it.

Running the ducting where I did ( which can be seen in the pic far above) means the range of steering lock has to be limited, to avoid having the wheel crush the 3 inch hose at full lock.
I opened up the bellows on the inner tie rod and steering rack, and placed a small hose (ring) clamp on the steering rack shaft, to limit its range. Since it is a de-powered rack, there is no worry about damaging a seal, or having the power to crush that ring with the steering wheel. So far that has worked out fine, but it is a race car, so only needs high steering lock occasionally.

HarryB

That looks nice; got any pictures of the end result?

Icedawg

Thanks.
If you mean the home made under tray, then no pic of the final result yet. But I can get pics over the next two days.
For the brake hose, the pic near the top is accurate, except it always slips to lie below the sway bar plane instead of beside it.

tfbmiata

I'd love to see more pics of the ducting and inside the wheel wells (i only see one if you meant to post more). I really want to have my brake ducts back but just bought a new and weirdly hard to find oem undertray and dont want to mangle it and f' up my engine cooling again. The only option i saw required a few 90 degree bends (or close to it) in the hose and cutting a large hole for the hose in the undertray and I just wasn't convinced the airflow would be great enough once those bends were added for it all to matter.

Icedawg

So pics, 'cause it did happen.
The hardboard undertray itself, along with the vertical remains of the original stock undertray. Ultimately I should make it out of ABS plastic, since hardboard will have trouble when wet. But hardboard is $12 (CAN) for a 4x8 sheet, and ABS is $58 to $108 depending on thickness. So I tried this first. Track is supposed to be wet this weekend, so I guess I will find out how delicate it is.



Then the installation of the vertical pieces on left and right sides.
In terms of routing of the brake ducts I was uncertain if this was the best approach, so I Googled Miata brake duct, and found this is by far the most common method applied for Miata race cars.







Then the view from underneath with the hardboard under tray installed, and full lock applied. But recall full lock is limited by ring clamps on the steering rack.
Screws with fender washers go into those clip pieces with threads, attached to the lip of the bumper, and the threaded plastic fittings at the outside edges where the stock lower wheel well liners went.
Where the paint is removed is where the tape goes on to seal the tray's lip. But eventually I want to put the stock "inverse gurney flap" back in place in front of the lip, so it will not need the tape.

And the views from the side, first with no wheels:
Driver side:

Passenger side:

And then with the wheels and full (restricted) lock dialed in. You can see the duct just clears the tire (a 245/40R15), and the strap holds it in place on the opposite, expanded side. It had a bit more clearance with 225 tires.

tfbmiata

Dude! You're awesome. Thanks a ton for the pics. I think i was trying to go at the same height as the sway bar and that pushed the hose into the tires, i think like yours if i skim some of the tray towards the back and push it under the sway that should give me enough clearance!