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Old 06-12-2013, 04:50 AM   #1
verentchan
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Default 2008 WRX DIY Brake Cooling Ducts (with pictures)

Hello all,

I took a look around and couldn't find a specific thread on brake cooling ducts on an 08+ WRX/STi so I decided to write my own. A little background - I'm a mechanical design engineer by day and I love to work on my Jeep and my new 08 WRX in my free time. I've gotten friendly with my mechanic after spending countless hours and thousands of dollars with him - shoutout to Ray at Extreme Auto Works in San Luis Obispo, CA for lending me the lift, extra hand and tools necessary to finish this job faster.

I purchased this WRX recently with a lot of work done to it already but I was preparing for a track day last week and I didn't want my brakes to start fading in the 100+ degree heat of Buttonwillow Raceway. The previous owner put the STI brembos on already, but I wanted to take it one step further.

Vehicle info:
2008 WRX Wagon
5x100 axles
STI Brembos up front
DBA 5000 rotors
Track pads

Now onto the mod:

I looked a purchasing cooling ducts but the ones I saw
1 - are expensive
2 - don't offer enough heat shielding
3 - and are designed for 3" tubing

I figured I could make my own for cheaper and I am totally right. Here's my design overview:
-3" Diameter inlet reduced down to 2" diameter to increase velocity and solve clearance issues w/wide tires
-high-temp hose necessary to prevent melting/deformation
-use foglight holes, make mod non-destructive to foglight mount

Skills and tools required:
-MIG/TIG welder and associated skills
-Power drill w/drill bits and 2" hole saw
-Wrenches/screw drivers
-Air impact wrench (optional, but much faster)
-car lift (optional but much faster

Parts to purchase or acquire:
-High-temp paint (I used this: VHT Flameproof) $8
-2" OD steel pipe, ~6" needed, and a few inches extra to hang onto when cutting, thinner the better $Free from scrap yard/exhaust shops
-2" Diameter stainless hose clamps (4x) $10
-3"-2" reducer coupling (2x) (this one) $28
-2" Diameter high-temp silicone ducting (~9-11ft) $53
-1/4" black drip irrigation line (~2ft) $4

I have extra if anyone wants some, just pay postage.
-2-part epoxy $5
Total parts cost:$108 without tax and shipping, could be cheaper if you have some of it already.

Procedure for dust shield:
  1. Remove front wheels, rotors, calipers, and bumper
  2. Cut 2" hole in stock dust shield close to hub center
  3. Cut 2" pipe at a slight angle, leaving about 2 in on the short side
  4. Clean parts with sandpaper/wirewheel/scotchbrite to prep for welding
  5. Weld a small lip on the square cut side of the pipe to prevent the hose clamp from slipping off the pipe
  6. Weld 2" pipe to dust shield placing angle appropriately to optimize clearance for ducting (tips: leave 1/8" of pipe protruding when welding to make it easier to get a good bead. The brake dust shield is thin so use TIG if possible, otherwise MIG weld at a shallow angle and in short bursts to produce a colder weld and prevent holes in the weld. You may also want to tack it in place then check fitment of the ducting before completing the whole weld)
  7. Clean off the welded parts of any debris and dust and spray with high-temp paint to prevent rust (You can see the lip in this photo. Notice that it doesn't completely surround the pipe because it is not necessary to do so and may actually make it more difficult to install)
  8. Allow paint adequate time to dry before handling

Procedure for inlets:
  1. Remove fog lights from bumper
  2. Take inlet reducer and cut the through hole on the 2" side
  3. Take the drip tubing and slit one side so that it can be slid over the inlet reducer
  4. Apply epoxy generously to the inside of the drip line and glue it over the sharp edge of the inlet. Cut it to length as necessary to minimize the gap (this serves two purposes: cosmetics and preventing the inlet from being pushed through the foglight hole into the bumper)
  5. Allow adequate time for the epoxy to set, clamping as necessary to prevent the drip line from coming off or shifting

    This is what they look like after applying the drip line to the edge but before cutting the hole on the 2" side.

Assembling it all together:
  1. Cut the high-temp duct in half and attach one end to the brake side with the 2" hose clamp
  2. Replace the rotors, calipers, and wheels
  3. Working toward the bumper, secure the ducting to the vehicle using zip ties. Check wheel clearances often, rotating the tire back and forth to make sure nothing rubs (hint: keep your keys in to disable steering lock and you can rotate the wheel by just pushing it around)
  4. Ensure enough slack for the wheel to turn properly without stretching the duct and stressing the zip-ties. Also try to keep zip ties away from high-temp areas such as near the exhaust manifolds/headers
  5. Replace bumper with the fog lights removed
  6. Pull ducting through the fog light holes as the bumper is replaced
  7. ensure about 2-3 inches of ducting is able to come through the fog light hole and trim any extra off
  8. Attach the inlet reducers to the duct with hose clamps and push into the bumper. It should be a snug fit and should not come out easily. If yours ends up coming out easily, you may want to consider adding some duct tape around the inlet reducer to give it more "bite" as it gets pushed into place. If you're having trouble sliding the inlet reducers into the soft ducting, try "screwing" the reducers in place because they have a spiral wire that runs through them.
  9. Admire your hard work!

    Note: it's not quite pushed in all the way here.

    So how did they work? I honesty have no metric to compare it to since I haven't had the car that long and I took it to the track for the first time after I finished the brake ducts. I can tell you thought that with race pads, front brembos, and these ducts on a high-speed circuit (110-120mph) with 100+ degree weather for four 30+min race sessions, the brakes experienced NO fade. The pads also barely wore even with 2+ hours of racing. I was hard on the brakes too, often times going too far and engaging ABS. I was running Castrol SRF brake fluid, and I'm sure that helped.

    Next on the list is to make some blocking plugs that are easily removable to prevent rain from corroding things in there and to prevent cooling when I want the brakes to get a little warmer (street driving, autox)
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Last edited by verentchan; 06-12-2013 at 05:02 AM. Reason: added prices
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Old 06-12-2013, 08:15 AM   #2
oguitar
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Awesome write up. Lately NASIOC has been lacking great write ups like the one you have provided.

I tried doing this on my bugeye a while ago and had issues with tire rubbing. I assume your tires are clearing the ducts adequately. Any pics of the clearance?
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Old 06-12-2013, 08:39 AM   #3
ride5000
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you could also just take the dust sheild off...
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Old 06-12-2013, 12:13 PM   #4
Patrick Olsen
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(1) I would've stuck with 3" hose. The velocity of the air doesn't really matter IMO. These setups invariably are routed with some abrupt turns, and I think it's more important to minimize the flow restrictions by using a bigger hose. Since you're able to route the hose along the underside of the frame rail, it doesn't appear to me that there would be any clearance issues using the 3" hose.

(2) Your "nozzle" at the dust shield look to give a pretty good shot to the center of the rotor, but I would have flattened it a bit to ensure some of the air wasn't blowing on the inner face of the rotor.

(3) While the inlet reducers make for a pretty clean install, I think they're suboptimal for flow (with that step at the reduction instead of a smoother transition). Instead of smoothly cramming 3" of air into the 2" hose, you really just have a 2" inlet.

The proof is in the pudding, of course, so if they work, they work. But I think they could have been a bit better.

Next time you go to the track, try covering the inlets with some painters tape to see what the difference is with and without the ducting. If you have an infrared pyrometer that will read high enough you can pull into the hot pits and take some quick measurements.
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Old 06-12-2013, 12:35 PM   #5
verentchan
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Quote:
Originally Posted by Patrick Olsen View Post
(1) I would've stuck with 3" hose. The velocity of the air doesn't really matter IMO. These setups invariably are routed with some abrupt turns, and I think it's more important to minimize the flow restrictions by using a bigger hose. Since you're able to route the hose along the underside of the frame rail, it doesn't appear to me that there would be any clearance issues using the 3" hose.

(2) Your "nozzle" at the dust shield look to give a pretty good shot to the center of the rotor, but I would have flattened it a bit to ensure some of the air wasn't blowing on the inner face of the rotor.

(3) While the inlet reducers make for a pretty clean install, I think they're suboptimal for flow (with that step at the reduction instead of a smoother transition). Instead of smoothly cramming 3" of air into the 2" hose, you really just have a 2" inlet.

The proof is in the pudding, of course, so if they work, they work. But I think they could have been a bit better.

Next time you go to the track, try covering the inlets with some painters tape to see what the difference is with and without the ducting. If you have an infrared pyrometer that will read high enough you can pull into the hot pits and take some quick measurements.
1) You're absolutely right - 3" would have netted less restriction. The mass air flow rate should be close though since that's determined by the inlet size (and then you factor in your losses due to turns, couplings, etc...). But the 2" helped me keep it pretty directed at the center of the rotor also. The 2" at the inlet simplified installation greatly and allows me the ability to remove the bumper easily (I have a full carbon splitter that runs back to the wheels, so I can't just reach underneath to detach)
2) If I had the 3" hose, I think I'd need a more directed nozzle. You also have the centrifugal action of the rotor in a sense sucking air from the center outward, since the larger openings at the outer diameter make a low-pressure zone relative to the inner diameter. Your idea to pinch it isn't bad, but starting with a 3" and then pinching it down, you probably net the same cross sectional area as my 2" circular nozzle. Then it would also introduce a restriction similar to my inlet reducer. It's hard to say what would be better.
3) Good idea, I think I'll try that!
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Old 06-12-2013, 12:37 PM   #6
verentchan
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Quote:
Originally Posted by ride5000 View Post
you could also just take the dust sheild off...
If I took the dust shield off I'd have nothing to mount the hose to and would have to purchase something or fabricate something. The dust shield was there already and strong enough to support what I wanted to do.
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Old 06-12-2013, 12:39 PM   #7
verentchan
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Quote:
Originally Posted by oguitar View Post
Awesome write up. Lately NASIOC has been lacking great write ups like the one you have provided.

I tried doing this on my bugeye a while ago and had issues with tire rubbing. I assume your tires are clearing the ducts adequately. Any pics of the clearance?
I'll have to take some later and post. I have about 2" of clearance, but I'm only running 225/45/17's right now on 8" width Enkei RS-M's. If I went to a 9" and larger tires, that gap will reduce significantly.
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Old 06-12-2013, 02:35 PM   #8
ride5000
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Quote:
Originally Posted by verentchan View Post
If I took the dust shield off I'd have nothing to mount the hose to and would have to purchase something or fabricate something. The dust shield was there already and strong enough to support what I wanted to do.
i meant take the shields off and dispense with this plumbing business..
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Old 06-14-2013, 06:29 PM   #9
sheldonjoe
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Thanks for this.

Aircraft spruce sells aluminum flanges you can use to rivet to the shield. I did this on my old S2000 and it worked great for me.
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Old 06-14-2013, 08:18 PM   #10
SweetSetofTools
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That 2-in. hose isn't nearly big enough to be helpful on this car, especially considering its length and the rough inner surface of the flex hose. As mentioned above, you'd be better off just removing this whole deal and pulling the dust shields.

In the photo just above #8, you can see that half the duct's area runs directly into the face of the rotor. This geometry not only restricts flow to the center of the rotor, but will also overcool the ID of the inner friction plate where the flow impinges, causing a range of potential problems from abrasive wear if you have track pads to accelerated thermal heating/cooling cycles, leading to severe surface checking or even major cracking in this region.
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Old 06-15-2013, 11:01 PM   #11
verentchan
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Quote:
Originally Posted by SweetSetofTools View Post
That 2-in. hose isn't nearly big enough to be helpful on this car, especially considering its length and the rough inner surface of the flex hose. As mentioned above, you'd be better off just removing this whole deal and pulling the dust shields.

In the photo just above #8, you can see that half the duct's area runs directly into the face of the rotor. This geometry not only restricts flow to the center of the rotor, but will also overcool the ID of the inner friction plate where the flow impinges, causing a range of potential problems from abrasive wear if you have track pads to accelerated thermal heating/cooling cycles, leading to severe surface checking or even major cracking in this region.
Hmmm that's definitely some food for though. Do you have more information about this? Case studies or examples of this happening? I definitely wouldn't want surface checking or cracking from the issues mentioned. I think what I need to do next is get some temp measurements and see what its effects really are.
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Old 06-15-2013, 11:02 PM   #12
verentchan
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Quote:
Originally Posted by sheldonjoe View Post
Thanks for this.

Aircraft spruce sells aluminum flanges you can use to rivet to the shield. I did this on my old S2000 and it worked great for me.
Any photos of your setup you can link to?
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Old 06-17-2013, 02:28 PM   #13
sheldonjoe
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Quote:
Originally Posted by verentchan View Post
Any photos of your setup you can link to?
I used this guy's DIY as reference: http://robrobinette.com/S2000BrakeDucts.htm
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Old 02-06-2018, 01:24 PM   #14
Speed Assault
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Quote:
Originally Posted by sheldonjoe View Post
I used this guy's DIY as reference: http://robrobinette.com/S2000BrakeDucts.htm
Thank You for the good write up. but cant find the 2" - 3" reducer anywhere,

Thanks Sheldonjoe for the other link where to buy

this will save me a fortune!!
thank you

Last edited by Speed Assault; 02-07-2018 at 01:22 PM.
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Old 02-07-2018, 03:05 PM   #15
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Quote:
Originally Posted by Speed Assault View Post
Thank You for the good write up. but cant find the 2" - 3" reducer anywhere,

Thanks Sheldonjoe for the other link where to buy

this will save me a fortune!!
thank you
Aircraft suppliers, like Aircraft Spruce, is one. Look for engine cooling ducts or cabin heating ducts, they use similar parts and likely also have the hose and other bits to think about.
Another standby for many things industrial is McMaster-Carr.

For the steel tubing, electrical thinwall tubing (EMT) can be had for cheap/free. Check a HomeDepot, local electrical contractors or suppliers, etc. Thin wall steel tubing, galvanized (sand or grind the area before welding, galvanizing fumes are rather bad for you). Maybe get some of their random cutoffs.
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Old 10-21-2019, 04:43 PM   #16
jacobe38
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hey OP, any learnings in the years since your original post?

im about to do some DIY ducting on my 2013 wrx.

a lot of my plans are similar to yours. im mostly interested if you found that 2" was still enough to be worth the trouble (im confident 2" is all i can fit) and if you had any issues with 'over cooling' on the ID of the rotor face.

thanks
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