Alternate Brake cooling at rotor

[Wil Ferch]

Guys 'n Gals:
Conventional wisdom says to route brake cooling ductwork to the front rotors...with the idea to bring cool air into the inner surfaces of the vented rotor. Some even add the little star plates to avoid short circuiting the air path...forcing air through the internal vented portion of the disc.
However, ...I'd like to experiment with ducting that goes directly to the outer opposing surfaces of the rotor ( through a "clamshell" as it were..like another, but empty caliper)...much like the early 917's. Fresh air now contacts the outer surface of the rotor, and you then cool the surface *imediately* instead of waiting for the brake to heat soak through the brake thickness itself. My theory being that you attack the problem sooner as the brake heats up.
Any advice on the pieces that could work for a stock 85 Carrera?
--Wil Ferch

[Joeaksa]

Wil,

If you find out anything interesting, pls post it! Always nice to improve braking!

Joe

[cstreit]

One difficult part of this would be making sure you try and balance cooling to both sides of the disc so that one side doesn't get much hotter than the other which might result in warping...

[Wil Ferch]

CStreit:
True..however it would be difficult to balance the air flow even under more normal conditions. Look at a thread on cryo treated rotors where Bill Verburg discusses and shows thermal images of a rotor...temps are all over the place..figurativley and literally. See page two of this post showing the clamshell I'm talking about..

Thinking About Drilled Rotors?

--Wil Ferch

[Bill Verburg]

AP recommends ~20% of the available air flow on the outer faces(10% inboard and 10% outboard) and ~80% thru the central vented portion. Air introduced at the axis migrates to the periphery because of dynamicaly induced pressure differential. It can't go the other way.

[Wil Ferch]

Bill:
This is interesting, but I wonder...why wait for the heat migration through the thickness of the rotor face(s)?.... when you can attack the problem at the source ??? Did any of your sources explain that...and also...did the pictures of the racing cars shown earlier indicate a second flow path to the eye? Doesn't look that way to me. Curious.
---Wil Ferch

[Bill Verburg]

Sure its been done the pic of a champ car showed one example, here is another of a clam/cooler on a 908


When a cars rotors are limited by wheel size that is the preferred solution. When there is no limit bigger rotors(both in diameter and thickness) are preferrred, and if money/rules are no object then exotic materials.

The motion of the rotor/wheel creates a region of lower air pressure at the periphery than at the hub, so there is a natural flow radially. This flow is significantly enhanced by properly curved rotor vanes, but is severely hampered by the clam shell shown above. This flow is less efficient when the wheel size barely accomodates the brakes radially. There have been numerous attemts to shape the blades of the wheels to enhance air flow thru the wheel(generally extraction from inside to out works best). The most successful was the 935 setup. The curved blades on 993tt wheels are another effort along these lines.

Here is a diagrm of such a setup on a McLaren F1 car


There can be numerous ducts to the eye here is one typical example use on a NASCAR stocker which is limited by 15" wheels

[89911]

Bill, your knowledge of brakes is outstanding. Nice work!

[Wil Ferch]

Super stuff !!!

Bump...back to the question...any clam type parts that may work for a stock 85 Carrera using 911-style 7x16 front Fuchs?

--Wil Ferch

[Bill Verburg]

Will, in a word no. The current state of the art, used in everything from NASCAR to F1 is a plenum. The McLAren F1 setup above is one example. Here is another suggested by Willwood for NASCAR short track apps.







You'll notice that the suggested location of the entry points are vertical and as close to the car center line(high pressure area) as possible. Do you see the resembleance to the Porsche GT2 inlets? They also recommend leading mounts for the calipers.

[Chuck Moreland]

Wil

I fashioned plenum type shells for my rear rotors. This because it is pretty much impossible to duct air into the rear eye.

I used the factory brake sheilds as a base to build upon.

[TimT]

Wil,

You may have to just fabricate your own clamshells, it really should be to hard. Whittle some foam cloack with glass,carbon, or kevlar, ( use the foam that dissolves when exposed to gas or carb cleaner.

Im sure you can buy the 935 or908 or whatever clamshells but they would be mucho dinero.

[mm86911]

Starting to acquire parts for cooling front brakes and would like opinion (have hub block-off plates, rotor hats and 2.5" hose). What is most effective:

1. Use readily available system with scoops under front control arms

2. Sans scoops and just run hose up to Carrera fog lamp openings (lamps already removed and covered with wire mesh)

Concern is that hose would be longer but also think airflow much greater. Thoughts?

[ChrisBennet]

Originally posted by mm86911
Starting to acquire parts for cooling front brakes and would like opinion (have hub block-off plates, rotor hats and 2.5" hose). What is most effective:

1. Use readily available system with scoops under front control arms

2. Sans scoops and just run hose up to Carrera fog lamp openings (lamps already removed and covered with wire mesh)

Concern is that hose would be longer but also think airflow much greater. Thoughts?

There are several scoops-under-the-A-arms products but the Cool Brake (tm) that OG Racing sells uses a 3" hose instead of the 2.5" hose that others use.
-Chris

[mm86911]

Chris - thanks for the recommendation.

I originally went with the 3" OG Racing kit but wasn't satisfied with the fiberglass components (molds must be getting old and finish work not as nice as I would like).

Just received the AJ-USA hats with 2.5" hose and Smart-Racing rotor/hub plates.

Bottom line question is what will provide best cooling - scoops under control arms (short hose) or routing hose to front valence at fog lamp openings (long hose)?

[ChrisBennet]

Originally posted by mm86911
Chris - thanks for the recommendation.

I originally went with the 3" OG Racing kit but wasn't satisfied with the fiberglass components (molds must be getting old and finish work not as nice as I would like).

Beauty is as beauty does. No one can even see them unless the car is up on a lift. I've been running mine for around 5 years I think. A couple of times I've busted the zip ties and the scoop has bounced on the road a little without any real damage.
-Chris

[Bill Verburg]

mm86911, The best place to pick up air is the front valance, like this, 6" more inboard on each side would be more efficient, but we need to use what we have.


To do so there are several other things that must also be done,

• move oil cooler to central position
• remove water bottle(it's too big any way)
• get the air past the inner fender while stilll allowing reasonable range of steering motion w/o restricting the flow of air too much

This last issue is the killer. Assuming that you do not want to hack up the trunk and run the lines thru it then perpendicularly out to the rotor hub the best solutions is sort of expernsive.




These are sold by S-Car-Go and Autometrics, probably others as well. They are a good solution because the smoooth inner surface does not promote the turbulence that ribbed tubing will, hence will flow much better, additionally the cross sectional area remains sort of constant, this is also a good thing.

Use the largest smoothest internally tube that you can find. 3" is pretty standard. Scat tube(orange) is good to 600&degF CAT(black) to 300&degF. Here is some of the available tubing
CAT-DXRL13 Flexflyte Hose, 3" x 12', Lined
CAT-UXRU13 Flexflyte Hose, 3" x 12', Un-Lined
CAT-DXRL93 Silicone Hose, 3" x 12', High Temperature
PSY-TPS12 2-Ply Silicone Hose, 3" x 12'. High Grade Mil-Spec
PSY-20724576 Silicone Hose, 3", Ultra-light with Memory Retention, High Grade Mil-Spec, sold per foot.

Anything hung under the A arms is sure to get ripped off in short order. SmartRAcing has an innovative solution which clamps around the A arm as shown


They are only 2.5" though. They do look like they could be easily made ina 3" configuration at a very reasonable cost if it's a DIY. If you do use something like this in a 2.5" size I would still use 3" tube w/ proper transitions like these.


At the intakes you will probably want to use some offset fittings like these

[mm86911]

Bill / Chris - thanks for the detailed info. Will be running ducts through front valance. . . likely to fabricate some ducts to improve velocity at intake

[Bill Verburg]

Ran across this setup done by Steve Timmins. It looks like what you willl want. Your sway bar hooks up ina less obtrusive way.


If you want to fab a Smart Racing type tube, 3" DWV from Home Depot would probably work.

[Litle brother]

Know this is a very old thread, but here`s a question for Bill:
- do you know where it is possible to get a ducting kit like the one from SmartRAcing ? Can not find it anywhere.

Regards
Eskild