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Brake cooler duct design (your input welcome)

Old 12-18-03, 05:39 PM
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Brake cooler duct design (your input welcome)

Im making some carbonfiber/kevlar FD brake cooler ducts right now and wanted some input on what experienced drivers would have to say about the design. right now im in the middle of designing where the hole will be for the air hole. I noticed after looking over some pervious designs that there are apparently 2 major differences in location of holes.

the first design is a fairly large hole which would blow air both on to the interior face of the brake rotor as well as into the eye of the rotor where the vanes are located. this would cool off the both the face of the interior rotor as well as vanes but im afraid that this design would first allow for uneven heating/cooling as well as less air current thru the actual vanes of the rotor. what are your opinoins on this?

the second is a smaller hole which is directed pretty much over only the eye of the rotor and would cool/push more air thru the vanes on the rotor cooling off the enitre rotor much more evenly. beacuse of the size of the hole, there would be more pressure as well.

the thing that im not really sure about is the size of the holes, at 5mph, it would definantly make a difference in how big it is but at 60-100mph or above, would it really make a difference? the amount of air at those speeds might beable to over come the pressure loss of the larger hole.

our eye size for the stock rotors are about 1.5 inches wide while our rotors are about 2-3 inches wide. If the first design where there is a large hole which blows air on to both the face of the rotor as well as the eye, would it be better for me to make 2 holes, a 2 inch hole which would be directly over the eye as well as another 2-3 inch hole above the face of the rotor. This would mean either 2 hoses would run to it but the pressure of the air would be held high. remember there is a limited space area in the wheel well where you would have to clear both the brake/abs lines as well as the steering rack/toe link (I think that distance is about 4 inches)

So I guess the man questions are...

What size hole do you think would work the best?
How many holes would you like to see? (It is possible to make a few holes which are about an inch to 1 1/2 inches in diameter which feed only the eye of the rotor)
Where would you like to see the hole located?
Would it matter if the inside faces of the rotor cooled down faster then the out side?

planning on trying to eliminate some of the problems of the old design such as the mounting holes as well as the inability of the other ducts to clear the brake/abs lines when at opposite lock (personally I like to get sideways and I must beagle to go form opposite lock to opposite lock with out any interference)

oh yeah, would you guys like me to design some kind of hose setup for you so that it wont/will reduce the rubbing against the inside of the wheel well/suspension components? Of course it would cost you more since it would cost me to design and get parts. Hmmm I could offer it as an option I guess.

Im also thinking about making fb/fc/rx8/anyother car brake duct coolers as well if there is demand for them, if I do, I will need the backing plates/brake shields off a stock car. if someone can get them for me, they can get a free set as I am giving BigIslandSeven a set of FD brake cooler ducts for free as he has generously sent me his to take measurements off of. The stock shields will not be harmed in the making as well, imp just tracing the locations of the mounting holes and ABS sensor on to a sheet of paper with a pencil (ok ok, perhaps a bit of graphite might get on to the shields but you can easily take care of that with an eraser )

oh yeah, look for the CF 99spec lips soon

Last edited by skunks; 12-18-03 at 05:44 PM.
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Old 12-18-03, 07:12 PM
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oh some food for thought on why and how these work (before i read this and looked under the car for more info/design ideas, i though that the ducts just blew air on to the face of the rotor but now i know different)

SOME THEORY:

One can never have enough margin to safety. And brakes are one area where you don't want to run out of margin. When it comes to brakes these margins are wholly dictated by brake temperatures, be it the rotors, the pads, or the fluid. Brake fade can be attributed to overheating pad material in part due to exceeding the heat sink capability of the rotor itself. Without anywhere for the excess heat energy to go it goes to the pad material which subsequently overheats...and we get brake fade. Given the speeds one can see on the track and the limited range of brake pad material that can withstand the demands on the track of a 3000lb vehicle with OE calipers any means of reducing brake temperatures would be beneficial. A way to cooler brakes is by ducting ambient air to the brake components most susceptible to overheating. The most common means is to direct cool air to the eye of the brake rotor. The air is then drawn through the rotor by the internal vanes between the rotor faces thereby cooling the braking surfaces and subsequently reducing brake pad temperatures. So given all this, enter brake cooler ducts. These brake ducts perform the above function by scooping cool air from within the pressurized wheel well and directing it straight to the eye of the brake rotor. They are not true dedicated ducting in the purest sense of the term because they do not draw their air supply from the nose of the car but instead rely on the air pressure built within the wheel well. And with hoses going to the front of the vehical there is ample differential pressure to drive airflow through the duct. Even though I have a big brake setup I believe that even the stock brake rotor setup, with the correct brake pad, would be quite sufficient for any slightly modified track vehicle thereby negating the absolute need to go rushing off and drop $2000 for big brakes.

taken from another webpage and modded just a bit

BTW: I would love to have some one with a stock set up go up against someone with a big brake kit in an auto cross course or a track.

Last edited by skunks; 12-18-03 at 07:14 PM.
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Old 12-19-03, 04:45 AM
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wow, nobody has any comments?
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Old 12-19-03, 12:03 PM
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Well, you asked a complicated question..

With regards to hose size and opening size, I don't know, I gave up on fluid dynamics back in college, and the calculations for that are beyond me. In reality, any air you can get down to the brakes is going to be beneficial, but you can go overboard on the cooling too, especially if you plan to run this on longer straightaways. On my FC for example, I have no ducts built yet, and at this time, I don't plan to. So far, it hasn't become an issue, but as I drive harder, it may.

I would see if a 2" hose directed to the center of the rotor is sufficient, before I started adding additional cooling. I believe that differential cooling will contribute to rotors cracking, so I wouldn't recommend ducting air to one face of the rotor.

As a racer, the ducts will get a lot of air from the front airdam, which is where we usually put our ducts. As a street car, that may not be as viable or desireable. Just depends on what you're going for.

Good luck!

PaulC
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Old 12-19-03, 02:36 PM
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You definitely do not want to have a duct blow onto the surface of the rotor - unless it blows on both sides of it. Still, it is better to direct it at the vanes of the rotor, since they are designed to help cool the rotor as a standalone, and aiding it in any way is a sure winner. As far as size of the hole/hose, unless you're a badass physicist (or whatever) I think it's more of a trial and error. My Mazda Comp ducts (which blow onto the face of the rotor... ) are 3" in diameter IIRC.

Let us know when/if you get something done, and how much it is. I need to replace the ducts I have since they're actually more harmful than not having anything, and I was going to do the same thing you're doing now. If they're comparably priced, I'd buy a couple sets.

Paul - I don't know exactly what your setup is, nor how the FC's fare as far as brakes go, but putting ducts on my Spec7 didn't help braking so much as it helped the life of them. Instead of going through pads and cracking rotors in slightly under a season, I've gone about three half seasons on the same set of pads and rotors. The braking force, AFAIK, didn't change any with the ducts, but the brakes have lasted much longer. Just FYI.
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Old 12-19-03, 04:32 PM
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Whichever design cools the rotor the MOST EVEN. I know IOPort or someone sells one for FB's that blows all the air directly on the rear face of the rotor. I also noticed that guys who used these were cracking rotors left and right. Im not sure about the opening size, but make you main goal to cool the rotor evenly.
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Old 12-19-03, 05:03 PM
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ahhh cool, so there is proof of a difference in cooling/heating on each side of the rotor as I suspected. hmmm as far as the design goes, the eye of the rotor (well for fd's are concerned) is about only 1.5 inches wide. If i make a 2 inch hole, wont it be cooling the inside face the same as a 3-4 inch hole would do?

right now, im going to be charging about 150 bucks for a set of 2 (or how ever much it cost me to make them + 10-15 bucks). It's either this or i get a job as a pizza delivery boy and use my FD as possibly one of the fastest pizza delivery cars on this island haha

Last edited by skunks; 12-19-03 at 05:17 PM.
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Old 12-19-03, 05:05 PM
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repost, please delete
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Old 12-19-03, 05:05 PM
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Originally posted by christaylor

Let us know when/if you get something done, and how much it is. I need to replace the ducts I have since they're actually more harmful than not having anything, and I was going to do the same thing you're doing now. If they're comparably priced, I'd buy a couple sets.

do you already have a big brake kit?
did you notice any difference in how many hard stops in a row you could do before/after the duct's were put in place?
how much was the set you bought for?
oh yeah, what kinda tubing are you using for the hose?
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Old 12-19-03, 05:16 PM
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Originally posted by skunks
do you already have a big brake kit?
did you notice any difference in how many hard stops in a row you could do before/after the duct's were put in place?
how much was the set you bought for?
oh yeah, what kinda tubing are you using for the hose?
This is in an FB, with stock brakes. As far as before/after, I really have no idea. I never drove the car before, and my dad didn't have a clue what he was doing then, either.

They came with the car when we bought them, but I want to say they were $100-150 new.

I don't have a hose connected between the opening in the valence and the duct. I had some dryer ducting in between, but it got ripped out in just a few sessions and I've never replaced it. I looked at some other cars in the garages and very few had ducts, the ones that did have the same setup I do: enlarged hole in the valence with chicken wire covering it then open space between it and the duct. Eventually, I think I'm going to use some more dryer hose to go from the front marker lights to the ducts.
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Old 12-19-03, 06:27 PM
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let me know when they are ready
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Old 12-19-03, 07:50 PM
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doublt post, delet please

Last edited by skunks; 12-19-03 at 07:54 PM.
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Old 12-19-03, 08:01 PM
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here is a pic of some design stuff, as you can see, the 2 inch hole centered above the eye is too big as it will still cool the face fo the inside rotor, u think a 1.5 inch hole wiht a coupler to a 2 inch hose would be good?
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Old 12-19-03, 09:58 PM
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whatever happened to the 99 lips in cf?
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Old 12-20-03, 12:14 AM
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Originally posted by mapmaker50
whatever happened to the 99 lips in cf?
hopefully they will be done soon, need more bondo
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Old 12-23-03, 05:05 AM
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hmmm apparently, hawaii autoX guys think that brake duct coolers do not work and that they are more harm then good, what are you thoughs abou this?

BTW: these guys say just change out your brake fluid and brake pads and you won't see fade...
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Old 12-23-03, 09:24 AM
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In autox your runs are less than a minute, so brake ducting would be more of a problem, your brakes need to be to operating temperature.

Mazda Comp has the brake ducts that attach in place of the factory dust shield on the FB cars. 1 big problem with them is when you bolt on a 1-1/8" front sway bar make sure you do not turn your front wheels. They must be pointing straight ahead or you will colapse the 3" hose openings against the fat sway bar.

The cheapest easies I have seen on the FB cars was running 2- 1-1/2" hose into the stock dust shields, once you knock a hole in to them.

John
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Old 12-23-03, 12:31 PM
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Chris,

Well, coming from a bigger car point of view (I used to open track my Trans Am), fade was the primary concern for me, as well as longevity. The Trans Am is underbraked, so a 20 minute session will generally result in fade, unless you run ducts, race pads, and hi temp fluid.

With the RX-7, fade is non existant. I'm aware that ducts won't improve braking distances, but I always used ducts to avoid brake fade, which the RX-7 doesn't need. Even so, I get a good 6 or more races on a set of pads, and I went the entire season on one set of rotors, so I think even ductless I'm ok.

PaulC
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Old 05-07-10, 11:14 PM
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Sorry to bump an OLD OLD thread, but I was searching google.

So I am thinking some 3" dryer duct would be good for the ducting work. I got some
MazdaSpeed brake ducts on my FB that I haven't hooked up yet. This may be the way.


Also, on a slightly threadjacked route... I cannot remember what car this was (nor the racing
series), but they were having cooling issues with their brakes. There were 2 cars with 1 team
each, and they both had different ideas on where to pull the air from. Team 1 had air being
pulled from a duct from outside, whereas team 2 had ducks routing hot air from the back of
the radiator. Long story short, both teams failed to finish, but team 1 ended up doing some
damage to the brakes, whereas team 2 got into a wreck. Something about having TOO cold
air (outside) cracking the rotors, while team 2 just used the hot air expelled from the radiator
to cool.
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Old 05-10-10, 10:50 PM
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Use RV sewer pipe instead. It works better and is really cheap/easy to replace when it gets torn up.
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Old 05-11-10, 11:46 AM
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Originally Posted by Jeezus View Post
Sorry to bump an OLD OLD thread, but I was searching google.

So I am thinking some 3" dryer duct would be good for the ducting work. I got some
MazdaSpeed brake ducts on my FB that I haven't hooked up yet. This may be the way.


Also, on a slightly threadjacked route... I cannot remember what car this was (nor the racing
series), but they were having cooling issues with their brakes. There were 2 cars with 1 team
each, and they both had different ideas on where to pull the air from. Team 1 had air being
pulled from a duct from outside, whereas team 2 had ducks routing hot air from the back of
the radiator. Long story short, both teams failed to finish, but team 1 ended up doing some
damage to the brakes, whereas team 2 got into a wreck. Something about having TOO cold
air (outside) cracking the rotors, while team 2 just used the hot air expelled from the radiator
to cool.
we do the 25 hours of thunderhill in december. being in the middle of winter VS summer is interesting, at 100F the engine runs hot, tires are hot etc etc

in the winter, on the honda without the hod and bumper, we can go out an do a few laps, and the header is cold to the touch. to even get the coolant temp UP we actually put a bunch of cardboard in front of it, basically we blocked off the whole thing.

the brakes still glow red hot, maybe 20F vs 100F air is a problem but more likely it has something to do with the brake design on that car.

also we got to talk to the guy who ran the volvo grand am team (grand something) and they had cut the headlight out and used it for a turbo intake, until they checked it and found that over 100mph the headlight went from suck to blow. under 100 it worked for ram air, over 100, air got sucked out.

they had 2 turbo intakes...
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Old 05-11-10, 05:25 PM
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Up until I put ducts on my FC (2900lbs with fuel and driver, 213RWHP) I was burning through front pads like crazy. I used the AWR splash shield replacements that have a 3" hole for the duct and routed the hoses to the stock foglight locations, with some scoops from pegasus installed inside the holes. The AWR ones direct most of the air into the hole but some of it goes on the rotor. I don't think they designed it this way to be better, just to be cheaper to fabricate. All of the fancy ones I've seen for other cars put all of the air into the center hole.
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