Topic: Brake Ducting Q: Add Duct Fans or Not?

We have a heavy car at 3300 lb with driver and at our last race, one of our drivers boiled the fluid during a yellow. This is despite having 13" rotors and cobra calipers (biggest bolt on options for a 95 tbird). He had to pump twice to slow down. We measured a temp of 580F on the disc after he pitted.

FIX 1: upgrade the fluid from ATE Super Blue (dry temp 536F) to Motul RBF 600 (594F) right before the next race. This will clearly help.

FIX 2: I built some ducting that dumps air from a front bumper hole straight onto the rotor. I made this by fiberglassing in some ducts into two holes in the bumper cover and then welding two metal tabs onto some scrap 3" tubing. Ducting is RV sewer hose from Walmart. Interesting and satisfying project.

I'm now thinking that while fix #2 should lower disc temps at speed by forcing air onto the rotors at speed, it might not have the same effect under caution because of the reduced vehicle speed.

Q: Should I now consider adding two bilge pump fans (130CFM for ~$20 each) inline with the ducts or potentially as a separate duct?

PROS: would force more air during cautions onto the rotors... Arguably when we need it most.
CONS: fans themselves could/would be airflow obstructions when the car is moving at speed. See pic of how much of the inside of the tube is blocked by the fan.

Will the pros of active cooling outweigh the cons? This is what I'd like advice about.

I'm clearly over thinking this problem but this is the fun of Lemons for me. The cost and fab time don't bother me; I just want some advice if the added complication of the fan ducts (either inline with my existing new ducts or mounted on a second bracket aimed at the caliper) is worth it. A second bracket is added complication and imo one more thing that can fall into the track. If I go with inline mounting, I could probably secure the fans more securely on the inside of the fender.

Existing ducts and brackets I just made
http://www.gunn.com/images/race9_duct1.jpgWe have a heavy car at 3300 lb with driver and at our last race, one of our drivers boiled the fluid during a yellow. This is despite having 13" rotors and cobra calipers (biggest bolt on option for a third). He had to pump twice to slow down. We measured a temp of 580F on the disc after he pitted.

FIX 1: upgrade the fluid from ATE Super Blue (dry temp 536F) to Motul RBF 600 (594F) right before the next race. This will help.

FIX 2: I built some ducting that dumps air from a front bumper hole straight onto the rotor. I made this by fiberglassing in some ducts into two holes in the bumper cover and then welding two metal tabs onto some scrap 3" tubing. Ducting is RV sewer hose from Walmart. Interesting and satisfying project.

I'm now thinking that while fix #2 should lower disc temps at speed by forcing air onto the rotors at speed, it might not have the same effect under caution because of the reduced vehicle speed.

Q: should I consider adding two bilge pump fans (130CFM for ~$20 each) inline with the ducts or potentially as a separate duct?

PROS: would force more air during cautions onto the rotors... Arguably when we need it most.
CONS: fans themselves could/would be airflow obstructions when the car is moving at speed?

Will the pros of active cooling outweigh the cons? This is what I'd like advice about.

I'm clearly over thinking this problem but this is the fun of Lemons for me. The cost and fab time don't bother me; I just want some advice if the added complication of the fan ducts (either inline with my existing new ducts or mounted on a second bracket aimed at the caliper) is worth it. A second bracket is added complication and imo one more thing that can fall into the track. If I go with inline mounting, I could probably secure the fans more securely on the inside of the fender.

Existing ducts and bracketry I just made
http://www.gunn.com/images/race9_duct1.jpg
http://www.gunn.com/images/race9_duct2.jpg
http://www.gunn.com/images/race9_duct3.jpg
http://www.gunn.com/images/race9_duct4.jpg



Duct fans I'm considering
https://www.walmart.com/ip/Attwood-Turb … t/14150765
https://www.five-oceans.com/articulos/2835-M2/2835-M2-C3.jpg





Thanks in advance.
Regards,
-g

Myopic Motorsport's #888 Ceci n'est pas une Citron Thunderbird ("This is not a lemon" but a 1995 tbird w/ 93 V8 swap + shopping cart rear wing + engine mounted frito maker)
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Re: Brake Ducting Q: Add Duct Fans or Not?

I would go without the fans.  I think with the change in fluid and the ducts you should be good.  We have a lighter car (2700-2800 ish range) and we used the Motul 600 and did not have a problem, but there again, we only turned 65 laps.

Skip "Mongo" L.
Team DadBod

Re: Brake Ducting Q: Add Duct Fans or Not?

Yes, fans are an improvement. Look at the Detmar 4" fans instead of the Attwoods. Remember that they're more sensitive to restrictions on the intake than exhaust, so mount the fan ideally at the front duct. Second, your rotor duct needs to direct air into the center of the rotor, not the inside disc face. Can you move the duct inlet closer to the center of the car, say right about your radiator duct? You'll have a little higher pressure air there.

4 (edited by Fishah 2018-05-14 12:44 PM)

Re: Brake Ducting Q: Add Duct Fans or Not?

I was always under the impression that cooling ducts should be aimed at the calipers rather than the rotors. They house the fluid that is going to boil... That's where we aim ours but I'm no engineer.

I think fans are unnecessary and will be a restriction at speed. We run ATE in our 3100lb 928, with no fans in our ducts, and we've never even had a hint of fade. In fact, I'm not even sure we're getting them up to operating temp...

And we just raced at 100 degrees at Willow Springs, with repeatedly braking from 120+ MPH.

Granted we use very expensive pads, OEM Porsche 911 rotors, and have four-piston Brembo calipers, all of which manage their temp very well and provide far more braking than our tires can handle, so they don't get pushed overly hard.

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5 (edited by ross2004 2018-05-15 07:59 AM)

Re: Brake Ducting Q: Add Duct Fans or Not?

Admin edit. No linking to other race series forums please.

Ok...... google search "the other race series" thread discussing brake ducts & fans.

Re: Brake Ducting Q: Add Duct Fans or Not?

Thanks for the differing opinions. The reason I aimed my ducts at the rotors (vs the caliper) was largely dictated by packaging and the mount points I had on my spindle. These holes were originally used for rivets to hold the brake shield to the spindle (which I sold off years ago) and were basically the only place to mount the duct. FWIW, maybe half of the airflow coming out of the 3" duct should dump into the center of the rotor but because of the spindle design (and where the ABS sensor is mounted) I can't really dump more and still maintain range of motion. If I used the caliper bracket as a mount point to dump air on to the calipers, anything I fab will likely hit the front strut that sits behind the spindle assembly when you turn the wheel too much.

As far as mounting the intake more closer to the center of the car, this would be problematic because I a pretty big radiator & oil cooler in the way.
To move the brake duct intakes up higher I suppose I could cut a hole in the actual front bumper (what sits behind the cover) but honestly, I think having a complete front bumper will be more useful to us than having slightly higher pressure air going onto our rotors.

We use decent brake pads (Raybestos ST43) so I suspect with the new fluid our system will be good enough. If not, thanks for the suggestions and I'll look at mounting the Detmar's as an "upgrade"

-g

Myopic Motorsport's #888 Ceci n'est pas une Citron Thunderbird ("This is not a lemon" but a 1995 tbird w/ 93 V8 swap + shopping cart rear wing + engine mounted frito maker)
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Re: Brake Ducting Q: Add Duct Fans or Not?

Rotor temp doesn't necessarily equal caliper temp or fluid temp.

A lot of race pads are happy at 600+°f. I wouldn't consider that too hot for the rotor or pads but definitely too hot for fluid. Don't forget there are seals in the pistons that need to deal with those high temps for 8+ hours if you're doing well.

Are the calipers painted?

You could add stainless or titanium shims between pads and pistons to help reduce heat transfer.

Are you sure the brakes aren't dragging slightly when up to temp? Can check sliders, sticky pistons, collapsing brake hose that holds pressure like a check valve, a master cylinder adjusted a bit too tight..

-Killer B's (as in rally) '84 4000Q 4.2V8. Audis never win?

Re: Brake Ducting Q: Add Duct Fans or Not?

We use just ram air ducts and RBF 600 in our 88 T-bird with 11” sn-95 mustang brakes and havent had issues.

The problem you’re havving is hot soaking, not the slow times under yellow. Those just help the heat hang around. With ducts, even going 30 mph os going to help a lot where you have them installed in the fog light holes like we do.

Fans would only be for hard fast runs followed by coming to a complete stop. For vented rotors, throwing air at the inner hub is ideal since that’s where the rotor pulls it’s air from then slings it out the edge. So you cool bothe the thermal mass of the rotor, and move air over the caliper along the edge of the rotor.

Mistake By The Lake Racing (MBTL)
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Re: Brake Ducting Q: Add Duct Fans or Not?

Someone, I think one of the 3PM TR7/RX7 guys, told me that the pros claim brake ducts don't really work until you're close to triple digit speeds, so fans are a good plan in a series where you're not usually going that fast.

How true is that? I'm not sure since I've never seen the source for the claim. But I'd believe it to some degree.


As far as where to blow air, I've always seen it ducted to the center of the rotor, even on professional race cars. Sure the fluid lives in the caliper, but it's far easier to cool the rotor. And heat travels from hot to cold. So if you can get the rotor cooler than the pads, the heat generated from braking will try to heat the rotor more than the pad. obviously it's not a perfect all or nothing, but it does help.

The center venting on rotors draws air from the center and exits it through the outer edge as it spins. Get the extra cool air to the center and you'll help that process.

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Re: Brake Ducting Q: Add Duct Fans or Not?

We added ducts on our Camaro and that helped a bunch....then we moved them closer to the rotor and sealed them to the bumper (like you have now) and that was all we needed to keep the brakes cool and happy.   The car was 3120 on the scales with in it, but we had smaller brakes then you guys do.   I don't think you would need the fans honestly.

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Re: Brake Ducting Q: Add Duct Fans or Not?

Guildenstern wrote:

For vented rotors, throwing air at the inner hub is ideal since that’s where the rotor pulls it’s air from then slings it out the edge.

+1. We got rid of those tiny cracks on rotor surface, and stopped eating wheel bearings every three-four races. Stock 1.6 Sentra rotors, 9.5" in diameter, 0.7" thick. 2" duct running right at the base of the hub, blowing air under the hat and a bit onto the inside caliper pad (those stopped wearing faster, too).

K Car Stalker

12 (edited by gunn 2018-05-15 11:25 AM)

Re: Brake Ducting Q: Add Duct Fans or Not?

jrbe wrote:

Rotor temp doesn't necessarily equal caliper temp or fluid temp.

A lot of race pads are happy at 600+°f. I wouldn't consider that too hot for the rotor or pads but definitely too hot for fluid. Don't forget there are seals in the pistons that need to deal with those high temps for 8+ hours if you're doing well.

Are the calipers painted?

You could add stainless or titanium shims between pads and pistons to help reduce heat transfer.

Are you sure the brakes aren't dragging slightly when up to temp? Can check sliders, sticky pistons, collapsing brake hose that holds pressure like a check valve, a master cylinder adjusted a bit too tight..

You've given me several things to think about as both calipers were fairly beat up after this one race.
The driver side caliper was dribbling a little fluid so clearly the piston seal had ruptured. I swapped this one out for another reman unit. The other one has a slightly torn piston dust boot but seems to work just fine. I'll check it after another track day to see if it needs replacing.

1) As far as painting goes, both of my calipers are as delivered from A1 Cardone. I never cared for ricing out my calipers especially as keeping them stock looking makes any kind of warranty or core return a non-issue.
Q: are you telling me that there exists some kind of spray coating to prevent Heat from transferring from the rotor or pad to the caliper? Wouldn't this thermal barrier also prevent the heat dissipation from the various fins on the caliper from working as effectively?

2) Until this post I've never heard of a brake shim. From what I can see, shim's can be installed to maintain contact between the Pat and the rotor ras the pad gets worn down. Will these two metals actually work as thermal barriers as well? In endurance racing though, won't the heat eventually soak into the shims and the brake fluid in the calipers will cook anyway.
They seem cheap enough and I suppose I could make them myself if I have any scrap stainless or titanium (not likely) around. FWIW, a 94-04 Cobra brakes are common enough that I can probably find something off the shelf. I'll put this as a secondary item (maybe try before fans) unless you think these things are ABSOLUTELY worth trying).

-g

PS. I still have this extra caliper laying around my office if someone wants it. I'll let it go for cheap as I don't need it and can't use it on my tbird (turns out that SN95 Cobra calipers & C4 vette calipers have the banjo bolt position in a slightly different spot). I can't use this caliper and it's too late to return it.
https://forums.24hoursoflemons.com/view … p?id=36437

Myopic Motorsport's #888 Ceci n'est pas une Citron Thunderbird ("This is not a lemon" but a 1995 tbird w/ 93 V8 swap + shopping cart rear wing + engine mounted frito maker)
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13 (edited by jrbe 2018-05-15 06:23 PM)

Re: Brake Ducting Q: Add Duct Fans or Not?

Google "titanium brake shim". Pretty sure you will find that they exist already for the calipers your using. Usual disclaimer of do it right and make sure they're not going to do something funny / fall out / get stuck / etc. They help reduce heat transfer from the pads, into pistons, that then heats up the fluid. It's a heat in vs heat out thing. Brake pad shims (meant to be thermal barriers) help prevent some heat into the system. A thermal barrier means the heat that was being dissipated into the caliper / into the air is now more trapped in the pad and had to find other ways out. Pad temp well go up some with thermal barrier shims. Seeing as the rotors were 600, they could likely deal with more. It can be a bit of a balancing act. You don't want fluid boiling but don't want pads melting down. Sounds like your car is way over to the boiling side from your info which is why I mentioned thermal barrier shims as something that could help.
Heat out of a rotor iirc is a surprising amount infra red and a lot less than I expected to air. I looked quick and couldn't find the numbers. Ducts can help if done well.
Having a heat shield behind the rotor (the factory ones that keep heat off the knuckle / ball joints) will trap a ton of heat in the rotor. Can trim that but keep it around the ball joints if you didn't already.

600°f is bad for brake fluid, seals, etc, not necessarily bad for friction material. I tried to dig for st43 temp / friction charts but, https://www.corvetteforum.com/forums/au … ood-b.html

No, no spray I know of to help reduce heat in the rotor / pad. That likely would be reducing friction in some way. I meant if the calipers are painted they can trap heat. Some rebuilt calipers are painted, had to ask...

I wasn't trying to steer you any specific way, just trying to help with possible culprits and offer some ideas that could help.

-Killer B's (as in rally) '84 4000Q 4.2V8. Audis never win?

Re: Brake Ducting Q: Add Duct Fans or Not?

I am far from an expert but here it goes:

The ST43's on our van prefer to be hot.  I am sure there are limits but with the C5 calipers and giant rotors involved, the dustbuster is "touchy" before the pads get hot.  I did see a table once (long since lost to me) that they functioned best at  400-430F.  I will say they modulate a ton better after 4-5 laps out-braking 80% of the field in a minivan.

Outside of one team so far, I have found no disagreements on the value of ST43's on pretty much any car they are made for.  Not an answer to the original query but a data point.

Re: Brake Ducting Q: Add Duct Fans or Not?

+10 to Generous ducting @ rotor center.

Also

A1 Cardone is known for some pretty dicy rebuilds, I go far to avoid.

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Re: Brake Ducting Q: Add Duct Fans or Not?

Honestly, unless you crack the caliper or something weird, just rebuild them yourself.

Mistake By The Lake Racing (MBTL)
88 Thunderbird "What's the word? Thunderbird!", "What's the Price? Thirty Twice!"
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Re: Brake Ducting Q: Add Duct Fans or Not?

Where do you get good replacement pistons to rebuild calipers yourself? I've been trying to find them for a while now.
Calipers have been so bad lately I have been collecting stuff to do electroplating (and reverse to get the rust off.) Good pistons have been the tricky part to source (for German cars anyways...)

-Killer B's (as in rally) '84 4000Q 4.2V8. Audis never win?

18 (edited by Guildenstern 2018-05-16 09:36 AM)

Re: Brake Ducting Q: Add Duct Fans or Not?

Good pistons? They make those?

I mean at that point you want a set of brembo or baer brakes, oem is still going to be oem.

Mistake By The Lake Racing (MBTL)
88 Thunderbird "What's the word? Thunderbird!", "What's the Price? Thirty Twice!"
A&D: 2014 Sebrings at Sebring (NSF), 2014 NJMP2 Jurassic Park (SpeedyCop), 2012 Summit Point J30 (PiNuts)

Re: Brake Ducting Q: Add Duct Fans or Not?

You can get pad backing plates thermal barrier coated to keep heat in the pad and out of the caliper.

gunn wrote:

Until this post I've never heard of a brake shim. From what I can see, shim's can be installed to maintain contact between the Pat and the rotor ras the pad gets worn down. Will these two metals actually work as thermal barriers as well? In endurance racing though, won't the heat eventually soak into the shims and the brake fluid in the calipers will cook anyway.

Titanium and stainless are not great at transferring heat, with titanium being better as a heat barrier.

The '93 Cobra calipers were aluminum and I'm pretty sure they're the same architecture. Much better material for conducting heat from the fluid, and lighter as well.

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Re: Brake Ducting Q: Add Duct Fans or Not?

Mind if I offer a suggestion?  The air needs to be ducted to the center of the rotor, not blowing 'on" the rotor face.  Modify your duct mount on the spindle so there is like a 1/16" gap between the duct and the rotor.  You can notch the tube around the ABS ring to get it as close as possible.

Here is pic of mine that I built for my '06 Mustang GT track car.  They have been working great for 4 years now.

http://i164.photobucket.com/albums/u9/VKZ24/2006%20Mustang%20GT/IMG_20130707_164850_352_zps73fc23ba.jpg

http://i164.photobucket.com/albums/u9/VKZ24/2006%20Mustang%20GT/IMG_20130707_165235_660_zpsd711cdc7.jpg

http://i164.photobucket.com/albums/u9/VKZ24/2006%20Mustang%20GT/IMG_20130707_165349_475_zps1f916368.jpg

http://i164.photobucket.com/albums/u9/VKZ24/2006%20Mustang%20GT/IMG_20130707_165305_484_zps7588b992.jpg

http://i164.photobucket.com/albums/u9/VKZ24/2006%20Mustang%20GT/IMG_20130722_212238_893_zps09b494af.jpg

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21 (edited by gunn 2018-05-16 02:23 PM)

Re: Brake Ducting Q: Add Duct Fans or Not?

jrbe wrote:

Google "titanium brake shim". Pretty sure you will find that they exist already for the calipers your using. Usual disclaimer of do it right and make sure they're not going to do something funny / fall out / get stuck / etc. They help reduce heat transfer from the pads, into pistons, that then heats up the fluid. It's a heat in vs heat out thing. Brake pad shims (meant to be thermal barriers) help prevent some heat into the system. A thermal barrier means the heat that was being dissipated into the caliper / into the air is now more trapped in the pad and had to find other ways out. Pad temp well go up some with thermal barrier shims. Seeing as the rotors were 600, they could likely deal with more. It can be a bit of a balancing act. You don't want fluid boiling but don't want pads melting down. Sounds like your car is way over to the boiling side from your info which is why I mentioned thermal barrier shims as something that could help.
Heat out of a rotor iirc is a surprising amount infra red and a lot less than I expected to air. I looked quick and couldn't find the numbers. Ducts can help if done well.
Having a heat shield behind the rotor (the factory ones that keep heat off the knuckle / ball joints) will trap a ton of heat in the rotor. Can trim that but keep it around the ball joints if you didn't already.

600°f is bad for brake fluid, seals, etc, not necessarily bad for friction material. I tried to dig for st43 temp / friction charts but, https://www.corvetteforum.com/forums/au … ood-b.html

No, no spray I know of to help reduce heat in the rotor / pad. That likely would be reducing friction in some way. I meant if the calipers are painted they can trap heat. Some rebuilt calipers are painted, had to ask...

I wasn't trying to steer you any specific way, just trying to help with possible culprits and offer some ideas that could help.

Yeah, thanks for the open discussion.

1) We got rid of our dust shields years ago. Someone actually bought them from me.

2) Fair enough about painting your calipers. I suspected that's what you wanted to confirm but I just wanted to make sure.

I almost forgot to mention. On the side that I had to replace the caliper because the piston seal was blown, we also cracked the rotor. Allegedly this was a decent rotor made in an ISO certified factory but let's be honest -- it was a $20 rotor.

Based on what everyone here has posted, we'll see how we do at the next track day with just the ducts and RBF600. If we go back to Laguna Seca for our track day, I know this is a higher speed track than Sears Point so our brakes will be put under more punishment.

Titanium Shims are $70+/set. Wow.
https://hardbrakes.com/index.php?main_p … 7656f0496a

For some reason, I'd believe this website over some random dude on a BMW forum that says they work well.
https://auto.howstuffworks.com/auto-par … shims1.htm

Myopic Motorsport's #888 Ceci n'est pas une Citron Thunderbird ("This is not a lemon" but a 1995 tbird w/ 93 V8 swap + shopping cart rear wing + engine mounted frito maker)
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Frito Making Tbird from 2018 Sears Pointless Engine Heat BBQ - http://goo.gl/csaet4

22 (edited by gunn 2018-05-16 02:45 PM)

Re: Brake Ducting Q: Add Duct Fans or Not?

Side question: ever cut titanium sheet yourself?
Hardbrakes sells these shields for $72/pair for 4 of them 0.02" thick made from 6AL-4V alloy (grade 5); I believe you really only need 2 to separate the hot ass pad from the two pistons as there's not much metal contact on the outside clamp.

Pattern seems simple enough and I have cheapie pads i can use as a pattern.
https://hardbrakes.com/images/large/products/TS-T-D0412_LRG.jpg

If the sheet itself costs 6"x3" costs  $6 for Grade 2 (vs Grade 5 which is what hardbrakes.com uses).

Grades Explained
https://www.onlinemetals.com/productgui … mguide.cfm
Thickness
http://cdn2.hubspot.net/hub/297063/file … abloid.pdf

Source
https://www.riogrande.com/product/Titan … oft/135204


Allegedly, something as thin as <0.05" can be cut with metal shears. Cutting the two holes would be the hardest part. These two suggested plates are either 0.018" or 0.03" thick
https://backpackinglight.com/forums/top … st-2008054

Is there a specific reason why Grade 2 titanium wouldn't be equally suitable as a heat shield?
Am I missing something here or would this seem entirely DIYable?
-g

Myopic Motorsport's #888 Ceci n'est pas une Citron Thunderbird ("This is not a lemon" but a 1995 tbird w/ 93 V8 swap + shopping cart rear wing + engine mounted frito maker)
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Re: Brake Ducting Q: Add Duct Fans or Not?

Oh, I did research because i have similar PBR calipers, if what let go was the DUST shield on the piston, they say let it go, they just aren't made to hold up.

So unless it's the actual keeping the brake fluid in seal, don't sweat the dust shield.

Mistake By The Lake Racing (MBTL)
88 Thunderbird "What's the word? Thunderbird!", "What's the Price? Thirty Twice!"
A&D: 2014 Sebrings at Sebring (NSF), 2014 NJMP2 Jurassic Park (SpeedyCop), 2012 Summit Point J30 (PiNuts)

Re: Brake Ducting Q: Add Duct Fans or Not?

Guildenstern wrote:

Oh, I did research because i have similar PBR calipers, if what let go was the DUST shield on the piston, they say let it go, they just aren't made to hold up.

So unless it's the actual keeping the brake fluid in seal, don't sweat the dust shield.

Agreed. On my passenger side, the rubber boot is torn but nothing was leaking so i didn't bother changing it out.
-g

Myopic Motorsport's #888 Ceci n'est pas une Citron Thunderbird ("This is not a lemon" but a 1995 tbird w/ 93 V8 swap + shopping cart rear wing + engine mounted frito maker)
2017 Sears Pointless Organizer’s Choice
Frito Making Tbird from 2018 Sears Pointless Engine Heat BBQ - http://goo.gl/csaet4

Re: Brake Ducting Q: Add Duct Fans or Not?

The piston boots are just to keep dust and water out from between the piston and the caliper. On a race car that gets serviced on a regular basis you don't need to worry about the dust boots if they get cooked and crumble and on the PBR caliper they always do!
If you want to go cheap you can use SS instead of titanium, it works almost as well. What the shields do is dissipate heat as much as shield the pistons from the hot pads.

When I raced my Mustang I used two 3"ducts per wheel. One to the center of the rotor and one blowing on the caliper. I later converted to Wilwoods as I could get racing pads much cheaper for them than for the PBR calipers.