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      11-17-2019, 07:59 PM   #1
dradernh
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Front Brake Scoops

This past summer, at the same time I had a shop install a jack point in the center of each side of my car, I also had them do something to get more air into the interior of my front brake rotors.

I did this because I’ve been experiencing very high rotor and caliper temperatures ever since I began running the car at the track. Even though there is air being ducted through the front bumper cover and into the area where the front braking components reside, little of that air is able to make its way into the center of the rotors and then out through the vanes. Without sufficient movement of air along that path, the rotors and calipers are going to get pretty hot - maybe hot enough to discolor the calipers and, possibly, burn them down.

Compared to the E36 and E30 that I used to run, there’s remarkably little room to channel incoming air to the center of the front rotors. There’s insufficient room for a 3” or 2” brake duct hose, and the car’s front knuckles/carriers effectively block almost all access to the interior of the rotors. Those parts can be seen at #2 in this realoem diagram: https://www.realoem.com/bmw/enUS/sho...diagId=31_0956.

The work the shop determined would be most effective in moving at least some air into the center of the rotors was to fabricate what they called an air “scoop”. This part can be seen in the photos immediately below.

This is a shot of the air scoop from the front showing its position relative to some of the suspension and braking components:

This one shows a close-up of the scoop; it gives an idea of how small the opening for incoming air is with the knuckle/carrier taking up so much space:


This shows the scoop from the rear, giving a glimpse of the brake duct exit in the bumper as well as showing once again the smallness of the opening into the center of the rotor:


The scoop is aligned such that it captures a portion of the column of air flowing out of the brake duct exit in the bumper assembly and redirects that subset of air into the center of the rotor. The shop told me that, relatively, it would have a greater effect upon caliper temperature than it would rotor temperature.

I’m not sure where I’ve managed to misplace the specific before and after temperature data; although, if I look at a rotor paint temp chart and a caliper temp strip, I’ll quickly be able to offer up the before and after temperature ranges for both components. If anyone wants that data, please feel free to ask, and I'll pull it together. The bottom line is that both the rotors and the calipers are running a decent amount cooler than they were, but nowhere nearly as cool as I’d like them to run.

The next step is going to be to take out the caliper pistons and examine the dust boots and piston seals. Regardless of their condition, we’ll probably just go ahead and replace the boots and seals with high-temp units. The principal reason for this is that my next event will be a two-day open-lapping event at Watkins Glen, a much higher-speed track than is the track I’ve been running since I had the car built. That’s Mid-Ohio, a handling track with only one high-speed braking zone, whereas the Glen has five high-speed braking zones and places high demands on a car’s braking system.

FWIW, BMW sells a caliper repair kit that includes only the dust boots. If you want caliper seals from BMW, you have to buy new calipers. That’s not necessarily a problem, as Brembo makes the boots and seals that go in their calipers, but the shop tells me they need to take measurements before I can be assured of ordering the correct sizes of those parts.

In the event someone else ends up needing the data, I’ll post the caliper piston sizes here once they’ve been measured.

––––––––––––––––––––––––––––––––––––––––––––––––––

Update: Here are three photos of a brake scoop taken when it was off the car:





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Last edited by dradernh; 01-13-2020 at 06:18 PM.. Reason: Show an Unmounted Brake Scoop
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      11-18-2019, 01:17 AM   #2
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Quote:
Originally Posted by dradernh View Post
I did this because I’ve been experiencing very high rotor and caliper temperatures ever since I began running the car at the track. Even though there is air being ducted through the front bumper cover and into the area where the front braking components reside, little of that air is able to make its way into the center of the rotors and then out through the vanes.
Yes, it's amazing how little of that air can be actually used for cooling. With slightly wider wheels, even without steering lock, that duct exit is just blowing air directly into the tire.

Quote:
Originally Posted by dradernh View Post
The work the shop determined would be most effective in moving at least some air into the center of the rotors was to fabricate what they called an air “scoop”.
Very interesting solution, please share the before / after temps. I'd love to see the amount of difference it makes.

Quote:
Originally Posted by dradernh View Post
There’s insufficient room for a 3” or 2” brake duct hose, and the car’s front knuckles/carriers effectively block almost all access to the interior of the rotors.
Earlier this year, I had a prototype that brought a 2" hose to the inside side of the rotor (basically cutting the dust shield), pretty much following the tie rods and not using the bumper opening at all. Of course, with vaned rotors you want the air in the center, which is why this scoop is awesome, especially hanging from the bottom of the strut like that (is that the only attachement point?). If I ever come back to needing ducting (*), I'll probably borrow that strut attachment, thanks!

(*) for now very wide front tires (less need to brake), plus 355mm rotors seem to do the trick.
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      11-18-2019, 01:29 AM   #3
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Very cool, thanks for posting the pics.
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      11-18-2019, 02:43 AM   #4
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Quote:
Originally Posted by msendit View Post
please share the before / after temps

this scoop is awesome, especially hanging from the bottom of the strut like that (is that the only attachement point?)
1) I have a note to myself to gather that data - once I've got it, I'll post it.

The local shop I use has suggested an old brake cooling trick: water sprayed wherever it's needed to keep the brakes cool. If I was going to keep running the car and this was a serious-enough issue, I'd probably look into that. As it is, I'm doing only one or two more events before hanging my helmet up, and so far the brakes are working well despite the seemingly too-high temperatures. Heck, the calipers still look like new when they're clean - they have no visible discoloration at all. I'm most curious to see the conditions of the dust boots and piston seals.

2) I think there may be another attachment point. I'll take a look the next time the wheels are off, and if it's there I'll shoot and post it.
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Last edited by dradernh; 11-18-2019 at 02:54 AM..
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      11-18-2019, 08:47 AM   #5
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First, I'm probably wrong. But I thought proper cooling on vented disks involved ducting cooling air to the outer periphery of the disc. When the intake tubes connect to the brake shield the brake shield is molded so that the channel travels outward to the disc outer edge.

The idea is to get increased airflow across the outside circumference of the disk and that sucks the hot air inside the rotor chambers to get extruded.
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      11-18-2019, 10:23 AM   #6
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Quote:
Originally Posted by ScottSinger View Post
First, I'm probably wrong. But I thought proper cooling on vented disks involved ducting cooling air to the outer periphery of the disc. When the intake tubes connect to the brake shield the brake shield is molded so that the channel travels outward to the disc outer edge.

The idea is to get increased airflow across the outside circumference of the disk and that sucks the hot air inside the rotor chambers to get extruded.
The goal is to pass as much air as necessary through the disc's vanes, thereby cooling the entire disc. Using a disc with vanes oriented to allow as much air as possible to pass by while introducing sufficient air into the interior of the rotor is the way to achieve that design goal.

Sufficient air is frequently supplied by a 3" hose that forces outside air from the front of the car into the interior of the rotor. That air then flows through the rotor's vanes and exhausts quite a bit of the heat that's built-up in the rotor.

You can read and see more detail in the Internal Vane Quantity and Quality section on this page: https://www.essexparts.com/essex-des...87M2f80M3f82M4
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      11-18-2019, 01:36 PM   #7
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Quote:
Originally Posted by dradernh View Post
The goal is to pass as much air as necessary through the disc's vanes, thereby cooling the entire disc. Using a disc with vanes oriented to allow as much air as possible to pass by while introducing sufficient air into the interior of the rotor is the way to achieve that design goal.

Sufficient air is frequently supplied by a 3" hose that forces outside air from the front of the car into the interior of the rotor. That air then flows through the rotor's vanes and exhausts quite a bit of the heat that's built-up in the rotor.

You can read and see more detail in the Internal Vane Quantity and Quality section on this page: https://www.essexparts.com/essex-des...87M2f80M3f82M4
I'm not seeing anything concerning funneling air to the rotor center hub area for increased air flow through the disk. It seems that increased air around the outer circumference draws the air through. Now funneling air to the hub or caliper for cooling may be beneficial for those particular components.

I'm questioning whether increased air flow to the rotor center hub area actually causes turbulence and minimizes hot air drawn out through the outer vents. But, I haven't read the above closely enough to be certain.

Last edited by ScottSinger; 11-18-2019 at 05:01 PM..
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      11-20-2019, 01:55 AM   #8
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Forgot where I found this
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      11-20-2019, 06:36 AM   #9
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Quote:
Originally Posted by goodNIGHT View Post
Forgot where I found this
It's off this page: https://www.apmotorsport.co.uk/produ...r-cp9440-front.

AP Motorsport also sells the M4 GTR brake cooling kit seen below. Another driver I met at the track has an M2 with both Essex Parts' AP Racing front brake calipers and a similar brake cooling kit feeding air into his front rotors via both 2" and 3" hoses. His setup would work for an endurance race. I limit my sessions to 15 minutes.

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      11-23-2019, 06:17 PM   #10
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Those look really nice for a one-off custom fabrication. Be nice if they were available retail. I'd go for them.
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      11-23-2019, 07:58 PM   #11
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Quote:
Originally Posted by ggggbmw View Post
Those look really nice for a one-off custom fabrication. Be nice if they were available retail. I'd go for them.
Once the shop sends me a bill, I'll post the cost here. Given the shop's history of racing success, and what it's built and still builds, I'm grateful every day that the invoice has yet to hit my inbox!
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      12-19-2019, 07:55 PM   #12
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Sub'd for more!
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      01-13-2020, 01:46 PM   #13
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I added three photos of an unmounted brake scoop to the first post. They show that there is only one attachment point, the hose clamp.
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      01-13-2020, 04:03 PM   #14
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Quote:
Originally Posted by dradernh View Post
I added three photos of an unmounted brake scoop to the first post. They show that there is only one attachment point, the hose clamp.
Interesting. I guess they are light enough that it works without anything else.
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      01-13-2020, 06:17 PM   #15
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Quote:
Originally Posted by msendit View Post
Interesting. I guess they are light enough that it works without anything else.
Yes, I did forget to weigh them - and to measure them! :facepalm

All I can say is that they didn't come across as being heavy (the aluminum stock from which they were made isn't very thick). I do know that if the shop thought a further attachment was warranted, they would have added it.
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