View Full Version : Specific Brake Duct Question

01-17-2003, 02:34 PM
Alright so I went to ace last night and got my hose and zip ties (already have duct tape )....

Yesterday I was talking to my auto tech teacher and I mentioned the idea of using dryer hose for brake ducting. Long story short (and I do mean long) he said that the air on ventilated rotors is drawn in through the bottom and released through the top. He said to make the piece that connects, or releases the air to the bottom of the rotor if possible. I need to know if this is true, before I start designing/cutting away at ****.

Also, he said he would let me borrow this laser thermomoter (sp) to use to see how effective the ducting works.

01-17-2003, 02:49 PM
I'm pretty sure air flows from the middle outward.

01-17-2003, 03:33 PM
from a site on Jags:

The primary cooling airflow is from the inboard side of the brakes to the inside of the hub and outward through the ventilated disk. The warmed air can then go either out through the wheel or inward under the car. The use of Kleenwheels prevents the first exit, so all the air goes inward.

then...read this page (http://www.nsxhelp.com/diy2/Real-World%20Brake%20Upgrades.htm)


01-18-2003, 07:48 PM
the ducts should be pointed directly at the back side cnter of the rotor. I agree with DSC.

there are some ducting kits for BMW that are pretty trick:

M3 Competition Brake Duct Kit
As used on our IMSA cars

A custom made front brake backing plate with sealing lip that precisely fits the inside of the brake rotor. Air is brought in from the front spoiler under pressure and forced into the center of the rotor and out through the vent holes. Provides superior cooling under hard use. Kit includes special brake ducts (install in fog lamp openings), 6 feet of brake duct hose, backing plates with 2.5" hose fitting (3.0" available by request), clamps and instructions. Requires R & R of wheel hubs for installation.



01-29-2003, 06:18 PM
I'm curious about tapering the end of the ducting right before it gets to the brake. Will this increase pressure/speed or just decrease flow?

01-29-2003, 08:04 PM
{disclaimer: I never did well in physics}
I imagine tapering the end would increase air speed slightly, as well as increase air temperature ever-so-slightly. If you tapered it off too much, you'd probably start losing air (i.e. pressure in the tube not letting as much air in through the front end) but if it was just a slight taper, I doubt it would make a whole lot of difference. If anything, I'd widen the 'neck' where the hose points at the disc, to "cool" the air before it hits the rotor. I don't think it'd make any measurable difference, but it would make me feel better. :)

01-30-2003, 12:19 PM
my brake ducts


02-04-2003, 09:01 PM
:cool: not done yet tho...

02-05-2003, 06:23 AM
looks good Dave!

02-05-2003, 10:36 AM
Hey, whats a good way to take rotor temps?
Honestly, I'm just goofing off, I don't get my brakes hot enough to need ducts, but I'd like to atleast see what they're doing.

02-05-2003, 11:07 AM
there is rotor temp paint you can buy. it basically changes color with heat. i don't think it's really neded for your application. just keep an eye on the rotors, the more heat the more little cracks will appear. the other sign of excessive heat, calipers and mainly the pads will begin to turn white, or the rotor hat can begin to discolor either white or a blueish color.

02-05-2003, 11:18 AM
i would say a pyrometer that you use to take tire temps, but i'm assuming brake temps are far higher than tire, and that a typical pyrometer would blow up if forced to measure such a thing.

02-05-2003, 07:29 PM
you use a laser pyromoter for the rotors and a probe type pyromoter for tires.

02-12-2003, 01:43 AM
Originally posted by DSC
I'm curious about tapering the end of the ducting right before it gets to the brake. Will this increase pressure/speed or just decrease flow?

Like a venturi??? If it was the shape of a venturi then it would probably increase the velocity of the air with negligable increase to air temp.

02-12-2003, 06:03 PM
you won't flow more air. the velocity only goes up because the area is smaller and the same amount of air is supposed to flow through a smaller area. I don't think it will help the cooling of your brakes any. It may not hurt, but I don't see how it could help. Also, if the walls of the tube you are using are really rough, like corrugated dryer venting, that will cause a lot of turbulance inside the tube and restrict more. If I was using that type of tubing (which I probably will) I would not want any more restriction from making a smaller diameter.

02-12-2003, 07:11 PM
Originally posted by DSC
Hey, whats a good way to take rotor temps?

Simple! After a hard run, turn your wheel to full lock, and stick your hand back there. if you get 3rd degree burns, it's safe to say you need ducts. 2nd degree burns, they'd help but not necessary. 1st degree burns, you're not driving your car hard enough. :D :p
(Disclaimer: I was kidding)