Brake cooling duct directed at caliper - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 26 Old 05-11-2011, 09:03 AM Thread Starter
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Brake cooling duct directed at caliper

On my car the cooling ducts are directed at the front of the caliper. This is a cobra brake setup. The ducts are Roush installed and evidently survived bondurant as this is a former school instructor cobra. A respected member of this forum (I am not going to throw him under the bus) said never to direct cooling at the caliper or atleast not to on this setup. Thoughts?

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post #2 of 26 Old 05-11-2011, 09:36 AM
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I've seen pictures of real race cars with air ducted to the calipers in addition to the more conventional ducts to the rotor hats. I can't see how cooling the calipers would be a bad thing, but I'd be curious to hear the logic from the as-yet-unnamed forum member - maybe there's something I'm missing.

Edit: What do you mean by the "front of the caliper"? Do you have any pics of this setup?


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post #3 of 26 Old 05-11-2011, 09:46 AM
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Larry Narcas who used to own Carbotech says that is the way to do it as that is where the heat is generated.

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post #4 of 26 Old 05-11-2011, 01:26 PM
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I think where you duct the air depends on the kind of fade you're getting. If you're boiling the fluid, cooling the caliper will help. If you're fading the pads, you need to cool the rotor, as cooling the caliper won't help much there. And it seems to me if you keep the rotor cooler there will be less heat going through the pads to boil the fluid in the first place, but I may be mistaken. Bottom line is my first priority would be keeping the rotor cool and caliper secondarily.
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post #5 of 26 Old 05-12-2011, 12:25 AM
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Quote:
Originally Posted by CSG View Post
On my car the cooling ducts are directed at the front of the caliper. This is a cobra brake setup. The ducts are Roush installed and evidently survived bondurant as this is a former school instructor cobra. A respected member of this forum (I am not going to throw him under the bus) said never to direct cooling at the caliper or atleast not to on this setup. Thoughts?
The most applicable rule of thumb is to aim 70% of the air to the center of the rotor and 30% to the caliper -- at least for iron discs. For cars that run carbon-ceramic, those ratios are reversed.

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post #6 of 26 Old 05-12-2011, 08:11 AM
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Originally Posted by MFE View Post
And it seems to me if you keep the rotor cooler there will be less heat going through the pads to boil the fluid in the first place, but I may be mistaken.
I dunno...the heat comes from the friction between pad and rotor. There may be some secondary heat transfer from the rotor to the caliper through the pads, but my bet is that most of the heat seen by the caliper is conducted from the pads' friction heat.
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post #7 of 26 Old 05-12-2011, 08:33 AM Thread Starter
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I appreciate everyone sharing their knowledge and opinions and look forward to hearing more. Hopefully the unknown person will see this and reply as well. I don't have a pic right now of these parts. If anyone is familiar with this setup I am wondering it was originally a cobra r part or something like that? The part at the wheel is a stamped steel oem looking piece and I am curious of it's origin.
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post #8 of 26 Old 05-12-2011, 12:38 PM
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Can you get pics?
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post #9 of 26 Old 05-12-2011, 12:44 PM
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Originally Posted by huesmann View Post
I dunno...the heat comes from the friction between pad and rotor.
Right, and a given amount of energy times a given level of friction over a given level of time = a given amount of heat. And the rotor is the primary heat sink. Let's think of it in terms of distribution paths.

I'm ignoring a few things next for simplicity, but if the amount of heat is X, and its two distribution paths are Y and Z (rotor and caliper), then you could say X = Y+Z. And the rule of thumb as pointed out above is that Y contributes 80% and Z contributes 20%.

If the rotor is not absorbing and shedding heat as much if it could if it were cooled more, the heat has to go somewhere else...and more of it will go into the pads and caliper than would otherwise be the case. Using the 80/20 rule of thumb as a starting point, if you reduce the rotor's capacity to 70% of system heat, that other 10% has to move to the calipers, so they're handling 30% of the heat, if they even can. A change from 80 to 70 at the rotor is only a 9% change in what the rotors are being asked to do, but a change from 20 to 30 at the caliper is 50% increase in what the calipers are being asked to do. And that's assuming they're even capable of it, in reality, at some point, we're looking at a net reduction in brake system function due to reduced thermal capacity.

Therefore, the way I see it, a small change in rotor cooling capacity makes a BIG difference to what the calipers see, and it takes a huge change in caliper cooling to equal the same effect gained from a small change at the rotor.

Last edited by MFE; 05-12-2011 at 12:50 PM.
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post #10 of 26 Old 05-12-2011, 01:03 PM Thread Starter
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Can you get pics?
I hope to get some this weekend. Has everyone already seen how Roush did the front mount of the torque-arm on these cars? I had not seen it before and if anyone is interested I can take some pics of that as well.

Items of interest on the car that I was never aware of include bracing from the front core support to the k-member sort of the same concept as the "z-brace" on the new mustangs. There is also bracing laterally across the spare tire well. I can make a thread on the car if any of this stuff interests anyone.

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post #11 of 26 Old 05-12-2011, 03:02 PM
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I did the center of the rotor cooling, so it can keep the wheel bearing cool, and directional vent outward thru the rotor.


Once I put these on a few years ago, never/ever had another brake fade issue.
More photos: http://www.dariusrudis.com/2009_Brake_Ducts

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post #12 of 26 Old 05-13-2011, 07:38 AM
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Originally Posted by CSG View Post
I can make a thread on the car if any of this stuff interests anyone.
+1 for this!
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post #13 of 26 Old 05-13-2011, 12:25 PM Thread Starter
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+1 for this!
I'll take some pics this weekend and start a thread. It certainly is not anything special but it has a few things that I had never seen done like the torque-arm mounting and some of the bracing. For what I paid for it I can't see how I could have possibly gone wrong.
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post #14 of 26 Old 05-13-2011, 10:45 PM
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The danger with directing cool air at the caliper is that you end up blowing cool air on the brake rotor, but not evenly on both sides. That will make the rotor crack.

PBR/Cobra calipers are not super stiff to start with. As aluminum heats up, it loses stiffness. Blowing air on it from that standpoint is definitely good.

How hot something gets in a brake system is a function of a number of things. Basically, the amount of work being done per unit time determines how much power has to be dissipated by the brakes (converted from kinetic into heat). The actual temperature that a given part will be raised to is a function of the thermal resistance between where the heat is generated and the part in question and the thermal capacity of the part. Calipers tend to not get that hot, since the brake pad is a good thermal insulator, despite the fact that the caliper doesn't have a lot of thermal capacity. The temperature also depends on how much heat is being extracted from the part, usually due to convection cooling (airflow).

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post #15 of 26 Old 05-14-2011, 01:20 AM
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One other thing to note in Darius' picture is the markings on the bolts. If the lines don't match up, the bolt moved. I use a small dab of white paint (a small bottle of white touch up paint) myself. If the paint is cracked, something moved.
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post #16 of 26 Old 05-14-2011, 06:54 PM
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Quote:
Originally Posted by Jack Hidley View Post
The danger with directing cool air at the caliper is that you end up blowing cool air on the brake rotor, but not evenly on both sides. That will make the rotor crack.

PBR/Cobra calipers are not super stiff to start with. As aluminum heats up, it loses stiffness. Blowing air on it from that standpoint is definitely good.

How hot something gets in a brake system is a function of a number of things. Basically, the amount of work being done per unit time determines how much power has to be dissipated by the brakes (converted from kinetic into heat). The actual temperature that a given part will be raised to is a function of the thermal resistance between where the heat is generated and the part in question and the thermal capacity of the part. Calipers tend to not get that hot, since the brake pad is a good thermal insulator, despite the fact that the caliper doesn't have a lot of thermal capacity. The temperature also depends on how much heat is being extracted from the part, usually due to convection cooling (airflow).
These are good comments. Allowing for some minor clarification, aluminum does NOT change stiffness to any measurable degree with temperature. Strength, yet, but not stiffness. Since we don't usually see OE calipers breaking, we need not worry about the temperature the caliper runs at for the sake of its parent material.

Where it does matter is the seals and fluid. Cook them too much and we'll be replacing seals often. And we will certainly know when the fluid starts boiling!

It is a good idea to vent about 30% of the airflow to the caliper to keep the seals, fluid and pads a bit happier -- provided there is ample airflow available. The focus of brake cooling (70%) needs to be the eye of the rotor so that cooler air gets pumped up through the internal vanes. As you've mentioned blowing cold air on one friction face often leads to early trouble.

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post #17 of 26 Old 05-14-2011, 10:15 PM Thread Starter
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They don't look quite I thought. Obviously air is directed directly at the front end of the caliper and at the inside of the rotor. I appreciate all the comments so for. I am curious what the opinions will be not that you can see what I am dealing with. I apologize for not having these pics before starting the post.
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post #18 of 26 Old 05-15-2011, 04:22 AM
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I did mean to say stiffness.

See here as a reference:

Young Modulus of Elasticity for Metals and Alloys

6063 loses 13% of its stiffness going from 70F to 400F. It does of course also lose strength as temperature goes up. And if the caliper was heat treated during manufacturing, now it has a new mystery heat treat

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post #19 of 26 Old 05-15-2011, 01:07 PM
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Originally Posted by Jack Hidley View Post
I did mean to say stiffness.

See here as a reference:

Young Modulus of Elasticity for Metals and Alloys

6063 loses 13% of its stiffness going from 70F to 400F. It does of course also lose strength as temperature goes up. And if the caliper was heat treated during manufacturing, now it has a new mystery heat treat
And those calipers are not made from 6063 (a standard wrought alloy). It is very likely they are using a casting alloy that has better thermal properties, losing less stiffness at 400°F. The affects of the additional heating and cooling are factored into the artificial aging that the designer specified into his heat treating callout, so no mystery there at all.

But in service, they don't normally operate at that temperature, unless the owner is replacing seals after every track event. 250°-325°F would be a more typical range as OE seals are not all that great. They get hotter at times in the braking zone, but quickly come down after the corner.

Regardless of all that jazz, better cooling is helpful for cars going to the track. We just need to get the most air to the eye of the rotor as possible, with about a third directed towards the caliper to stave off fluid boiling.

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post #20 of 26 Old 05-15-2011, 06:50 PM
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http://http://s781.photobucket.com/albums/yy96/CSG_2010/
http://i781.photobucket.com/albums/y...0/IMG_3912.jpg
http://i781.photobucket.com/albums/y...0/IMG_3910.jpg
http://i781.photobucket.com/albums/y...0/IMG_3913.jpg

They don't look quite I thought. Obviously air is directed directly at the front end of the caliper and at the inside of the rotor. I appreciate all the comments so for. I am curious what the opinions will be not that you can see what I am dealing with.
Those are frickin' crazy looking! I've never seen a setup like that before. Seems like a needlessly complex design - rather than having the pipe that blows into the center of the rotor in the center of the duct inlet, it would seem simpler to just split the duct. Perhaps it's more efficient they way they designed it.

Anyway, thanks for taking the pics. Back to your original post, I would tend to agree with you - if Roush/Bondurant set those ducts up on a Bondurant school car I have to think they work. I wonder if the duct blowing on the caliper was intended to help prevent the clamshell effect that the PBR calipers are susceptible to?

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post #21 of 26 Old 05-24-2011, 12:49 PM Thread Starter
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I went ahead and re-installed the ducting to these. The ducting consists of a formed steel tube from the foglight opening back a few inches then it turns in towards the framerail and runs back probably 10 more inches. From there a flex duct connects the two pieces. I put in new XP-10's all around with a light cut to the rotors and new fluid. Will be trying it out Saturday at MSR-H for the revolution driving school.
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post #22 of 26 Old 05-24-2011, 12:59 PM
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IMOHO, the ducting (metal part funnel down) is WAY too small for airflow VOLUME.
Try this run WITH and WITHOUT the metal guard on onse side of the car. You will then truly find the answer, and be surprised as much as I was.
Vintage Venom did at one of my events, and there is a whole thread on them NOT running ducting, with cooler temps...

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post #23 of 26 Old 05-24-2011, 11:42 PM
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On the Fox body A Sedan car I used to crew on we blew air at the center of the rotor to cool the rotor and the wheel bearings. A second, smaller hose was directed at the PBR caliper. We have continued this practice on the RX7's we race now.

For us the answer is both following a 70/30 rule - 70% of the air on the rotor and 30% on the calper.

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post #24 of 26 Old 05-27-2011, 08:02 PM
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Where did you get the Blue Hi Temp ducting...?

Quote:
Originally Posted by drudis View Post
I did the center of the rotor cooling, so it can keep the wheel bearing cool, and directional vent outward thru the rotor.


Once I put these on a few years ago, never/ever had another brake fade issue.
More photos: http://www.dariusrudis.com/2009_Brake_Ducts


Hi there ! Where did you get that Blue Hi Temp Ducting Hose... All I can find is Orange color, and is a bit off for me...?
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post #25 of 26 Old 05-27-2011, 08:34 PM
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The orange hose is rated to 550° and is rediculous overkill for a brake duct setup. If the hoses ever get to 550° its because the car is on fire.
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post #26 of 26 Old 05-31-2011, 10:20 AM
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Dont remember (2009?) but its the 550'F version, as that is double-wall, and I got it for the durability 2-wall, not so much for the high temp.

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