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Brake cooling kit question

The standard brake cooling kits appear to vent cool air to the inside of the rotor. I remember seeing the 917 brake cooling "clamshell" that vented to both sides of the rotor (and down the middle of the rotor). I think it said that the clamshell was better, because it would not warp the rotors by cooling only one side. I am guessing I read this in B. Andersons book.

Anyway, do the standard kits (available here) pose problems with only cooling the inside of the rotor, thus causing them to warp?
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Old 05-07-2012, 07:54 AM
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No, they don't. As I recall, one of the first kits available was the Cool Brake from Holbert's back in the 80's when I got started. The AJ USA has been around for a long time as well. I think Jason over at Paragon Products sells something called the NERP kit.


Or one can fabricate their own. I always suggest coming up with a way to seal off the backside of the rotor opening since the kits cannot accommodate all sizes of rotors. I fab plates out of carbon fiber and carbon kevlar for this purpose. But thin sheet metal or fiberglass can be fine as well. These pieces can be attached to the kit's backing plates to enlargen the ID, or if one is clever and motivated, one can just make their own backing plates to attach to the spindles and/or struts.

Years ago, Smart Racing Products made and sold some thin sheet metal deflectors for certain 911 hubs to ensure that all air introduced into the rotors via the backing plates would be forced through the rotor vanes. I cannot remember for sure, but I think Craig (now the chief engineer for the Lizards) got the idea from age-old racing approaches. This concept is also described in the Puhn brake handbook, which I recommend as standard reference material for the more complete libraries.

Even if SRP no longer sells these, they are easy to fab up. I always make my own.
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Old 05-07-2012, 08:41 AM
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with more time than money i used the end plates from my black & decker bench grinder with a tad of sheet metal. welded some rigid EMT steel conduit to it then hole sawed it and for the spindle.









all the ducting was added with the pipe cut around the a arm with venting collected from bumper inlets
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Old 05-07-2012, 09:26 AM
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oh, and i also used old motorcycle tubes to cover the scat ducting to prevent chaffing in area where it made contact with the body, sways and a arm.
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Old 05-07-2012, 09:28 AM
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I was thinking about fabbing my own out of sheet metal. I do like the scoop idea that attaches to the a-arm, as my right front spoiler hole is already being used to duct to my oil cooler. I plan to replace my rotors soon, so it will be an excellent time to remove the backing plates and slap a brake cooling device.

Any other tips on fabbing? I do weld, but don't do fiberglass. I am not really interested in spending $$ on something a child could do for $30.
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Old 05-07-2012, 10:52 AM
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Keep the ideas coming ... i'm facing the same dilemna as i need to adapt something for my 996TT brakes for which the Ajusa backing plate kit is too small !

Cheers !
Phil
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Old 05-08-2012, 05:25 AM
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Wildcat, why not use the Cup Car duct and plate? Should fit...
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Old 05-08-2012, 10:45 AM
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Chris,

Which part would that be,guessing it's from the later 997 Cup cars ?
I now have 13 inch rotors in the front so the regular 911 stuff doesn't work for me anymore ...

Cheers !
Phil
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Old 05-08-2012, 11:53 AM
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The internal blocking plates SmartRacing sold block off the holes in the "spokes" in the 911 (pre-964 anyway) hubs. The Cool Brake kit came with these, and a small tap and some screws - the idea was that you drilled your rotors (which is what these attached to), tapped, and secured with screws. At rotor replacement time, unscrew and transfer over to new rotors, drilling and tapping as required.

I quickly modified this. First, I made my own out of thin aluminum. Don't really even need to make holes for the rotor/hub bolt ends to stick through. Then each time I just drilled the new rotors through the old holes, and pop riveted these into place.

Any old thin aluminum, easily cut with shears into an annular ring, will do. Strength not needed here.

The main defect of the A arm scoops is their tendency to get busted off fairly promptly, especially in the learning stages of ones track experience. A secondary one is that they get relatively hot air right off the tarry surface.

What a guy wants is to put his front oil cooler into the center of a valance made for that purpose. These cool enormously better than anything you can put in a fender. And then use the two brake ducting openings for their intended purpose.

That leaves only the hoses/pipes, duct tape repairs, pieces of aluminum wrapped around where the tire rubs as armor, etc, to deal with.

Assuming you have fabricated something to replace the factory dust shield to hold the hose end and keep most of that air going into the center of the rotor. Using Mitch's expedients or something else.

But perhaps I discount the value of late style curved air guides that Porsche uses. With front oil coolers, water radiators, and their air passages, perhaps there was no room for brake cooling air pickup left on the front valance?

To address your original question, I believe that the clamshells have gone out of favor, as I think they are not as efficient as having cold air go through the ventilation passageways which are built into your rotors. Must be better to force air into these, where it has a way to exit quickly enough, than to force it into external surfaces, which have a very much smaller surface area, and where it may have a hard time getting out? I think some early race cars had several clamshells? Between those, and sometimes even two calipers per rotor?, a whole lot of the friction surface was isolated from "natural" cooling.
Old 05-09-2012, 07:29 PM
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Vestiges of my late '80s Holbert Cool Brake kit are still on my SC - the backing plate with its hose attachment. Durable piece if you don't change rotor sizes. Also the short hose which used to connect to the brake scoops, not attaching to a longer hose. The scoops, with many repairs, are somewhere in my junk box I think.
Old 05-09-2012, 07:31 PM
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The rotation works with you when you feed air into the center. It is a centrifugal pump. With the clamshell you fight this effect. Much like how the 917 had its crankshaft oil fed in through the center and could use much less (and more constant with rpm) oil pressure versus the 911 which needs lots of pressure to fight the centrifugal effect.
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Old 05-09-2012, 10:37 PM
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Quote:
Originally Posted by cstreit View Post
Wildcat, why not use the Cup Car duct and plate? Should fit...
Got creative yesterday and started fabricating some home made "Ajusa " style cooling plates for my 13 inch front rotors ...

Forgot how difficult it was to weld .030 tin with a 215 amp welder and .035 wire
Going to dig out my little Lincoln 110 today and try .030 flux core instead !

I'll post pictures later on.

Cheers !
Phil
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Old 05-10-2012, 03:34 AM
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Looking foward to it, Phil.

Can anyone explain the design of the standard plates. That is, why are they a complete circle, rather than just a hose holder to point at the rotor face? Do they need to have a lip? What diameter of backing plate is optimal ... compared to the rotor diameter?

I am assuming that the cooling comes from 2 areas: 1, the inside rotor face receives cool air directly on it, and 2, the high pressure area created by the cooling plate / hose, forces cool air into the middle of the rotor, where it is spun through the vanes and out the edges of the rotor.

Does that all sound correct?
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Old 05-10-2012, 05:39 AM
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I suggest buying or borrowing the Puhn book.

For DIY, I think Toby's pics and approach are really helpful to study.

For the backing plates, you can use a variety of materials. Thin metals like aluminum are fine. You need to be able to scribe circles, so a compass helps, but you can use circular shapes in your shop as a template... like the bottom of a paint can.

Ideally, the backing plate will have an OD that exactly matches the ID of the inside of the rotor. This will ensure that all of the available air is available to get pumped through the rotor vanes, which is the goal. In my case, I had bought the AJ USA kit 10+ years ago, but the OD of the supplied backing plates was smaller than the ID of my rotors. I could have simple expanded that OD with a ring of aluminum attached by rivets. But I had a need for a project and some composite materials laying around. I found that one of the generic sizes for cheap metal electric oven burner covers provided a perfect mold to make composite backing plates with the OD I needed for my rotors, so that is what I used. I decided to use some left over carbon-kevlar as opposed to fiberglass.

The hub blocking plates are also intended to make sure the air goes where you want it. Some Porsche hubs are designed such that the plates are redundant, and in any case, we aren't talking about a lot of air that can get through. But I feel that if you are going to add cooling, it is worth fabbing some up depending on your hubs.

How much brake cooling one needs depends on their car's configuration and the demands of the tracks they drive. I always suggest that folks connect with others that have experience with similar cars that drive the tracks in their area to get ideas for configurations that will work.
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Old 05-10-2012, 07:52 AM
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Regarding "lips," no they are not necessary. Again, the goal is to seal the back side of the rotor.

I have not studied the physics, but I thing all of the major cooling comes through the vanes.

One old school approach I have seen has thin alu with an OD slightly larger than the rotor backside opening ID. In this case it was maybe 40 or 60 thou. The metal contacted the rotor surface ever so slightly. No issues.

That was on an IMSA championship car.

Some (perhaps all?) 962s not only cool the rotors with ducting, but also the front wheel bearings. Ask me how I know...
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Old 05-10-2012, 07:56 AM
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I think the best place to direct cool air for brakes would be the two outer surfaces where the pads ride- that is where the heat is being generated. F1 teams run ducts to the caliper/pad area (as well as everywhere else). But the wheel bearing cooling you mention is a good point.
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Old 05-10-2012, 08:43 AM
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Keep in mind that the clamshell design could create wheel clearance. If you're running large brakes and 16 or 15 in. Fuchs, you can have clearance issues between clam ducts and the wheel inner barrel.

Pelican still carries the plates that go between the rotor and the hub

Pelican Parts.com - Brake Air Deflection Plates


The typical backing plates that shoot air into the center of the rotor are usually just a smidge smaller in diameter than the ID of the rotor. Keeping the plate OD close to the ID of the rotor reduces air spillage. Since your cooling air is challenged by the hose size and bends in the hose, the flow is not all that great. Any leaks in the system are going to reduce the effectiveness.

The reason the plates have a lip on them is to stiffen the plate. W/out the lip, or if your plate material is thin/flimsy, the plate can flex in & out a bit. The flex is created by turning the wheels. Since the routing of the SCAT hose is usually a bit tight, the hose is also putting some pressure on the plate. When you turn the wheels, you can create more or less load on the hose and that in turn can make the plate move.

I made my own clamshells for the hose out of PVC drain pipe to go thru the A-arm support bar. It helps with the difficulty of routing the cooling hose entirely over the A-arm and avoids most of it being crushed during suspension compression

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Old 05-10-2012, 08:50 AM
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Like many things, the answer is it depends.

Again, the age-old Puhn book goes through all of this stuff.

I am not sure about the "two outer surfaces where the pads ride," but that doesn't seem right to me.

I think different types of cars and circumstances yield different types of needs. Further, various configurations of modified Porsche street cars (made into racing cars at the extreme end of the continuum), and dedicated racing cars have been developed and optimized through many years, so there is no need to reinvent the wheel or make guesses.

The lips on the AJ USA set up may be intended to add stiffness, but that isn't crucial in this application. Also, depending on the hub/rotor parts, there can be a slight distance between the a flat backing plate and the rotor. A "gap" if you will. That is the case with my Wilwood rotors , Bilstein RSR struts and SC hubs. So for my application, I have a lip in the composite parts. The AJ USA parts came in two sizes, for two different types of Porsche rotors. They may have the lip to help with a gap as well.


Again, what we are trying to do is make sure as much of the ducted air as possible goes where we want it. If the lips add more than $0.01 of cost to the manufacture, I wouldn't sign off on it. The Bob Russo/Holbert Cool Brake kits from the 80's had just flat fiberglass. If you want extra stiffness when using a metal, you could just go to a thicker gauge.

I think two different types of clamshells have been discussed in this thread. I believe that the initial reference is to a cooling approach taken by Porsche and Porsche-supported teams for certain 911-based racers like some 935 cars. I have seen these as I have had ready access to various examples at local events and shops.

The latter reference is to a method of ducting which includes an arrangements to deal with the 911 (and perhaps 914) chassis components/geometry in routing of the air. SRP (maybe Craig Watkins, maybe Jerry Woods, maybe someone else there) came up with something they made and sold called "manifolds." I have a set of these. They can be easily made from things like alu or PVC or composite tubing. So one can make them, or when SRP sold them you could just buy some. Time versus money. Well, time, cleverness and the desire to have some fun fabbing stuff in one's shop. Lots of threads on this here on Pelican.


It is not rocket science, and we don't need to reinvent the wheel.

962 front wheel bearings likely need/want cooling due to loads created by..... aero. Ask me how I know.
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Old 05-10-2012, 09:42 AM
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I'm confused. Do you like discouraging discussion on a discussion forum?

You always say this stuff has been done before and one should call the guys who are pros who have been there, done that. Then proceed to elaborate how it's been done......

My comment about the lips wasn't to say they are required. Just pointing out what benefit the lips can provide. By putting a lip around the perimeter, you stabilize the outer edge and hold its shape better. Think of a fender lip on body panels.

My plates are made by SmartRacing and are very heavy gauge aluminum sheet with lips around them. Maybe Craig & Co. like to overkill stuff. They were stamped, so including the lip contour in the die is not a big deal.

Nobody's trying to reinvent the wheel and say their cat-skinner is the best. Just pointing out varying ways things have been done, be it by retail purchase or copycatting those retailers' designs with backyard DIY "fabrication" skills.

Thanks for the clarification on the clamshells. I should have used a different term. However I think everybody can see that the clamshell I chose to describe, clearly has nothing to do with the calipers & rotors in terms of it's installation location.
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Old 05-10-2012, 10:37 AM
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Quote:
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backyard DIY "fabrication" skills.
i prefer it to be described as "more time than money", but that above will work...
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Old 05-10-2012, 10:49 AM
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