Brake Ducts

[the bruce]

Hey mate !!

Nice job, but I need to make some remarks:


1. By doing it this way you are blocking half of the area of your ducts >> a bad idea !!

2. Better fit one or two "air guides" / "deflectors" inside the inlet similar to my figure below.

3. I still believe you loose performance if you don't remove most of the brake shield (I know I'm boring).


At least the two black marked deflectors (even better add the green):



Many ducts (intakes etc.) have similar guides inside. In this windtunnel similar deflectors are used:




Pardon me, I didn't find proper pics on the web showing these deflectors in ducts and also didn't want
to take photos from  Joseph Katz' "race car aerodynamics" book.

 

[rex]

First of all, thank you for your advice!

1. By doing it this way you are blocking half of the area of your ducts >> a bad idea !!

Yes, the area where the air exists is smaller, but the same amount of air travels through there.
Because the exist is smaller than the intake, the air will travel faster through the exist.

2. Better fit one or two "air guides" / "deflectors" inside the inlet similar to my figure below.

I am not sure this way really solves what I want to do... I want to direct the air towards the disc vanes / disc bell and NOT directly on the inner side of the disc.
In the case proposed by you,here is the air flow through the brake ducts:



As you can clearly see, some of the air is directed correctly and some is not directed correctly.

This is the way I am thinking of making that part:



In this case, all of the air is going where I want it to go...

3. I still believe you loose performance if you don't remove most of the brake shield (I know I'm boring).

I agree, but the only reason to keep the dust/mud guard (shield) is that my car is is still a daily drive and a lot of dirt/dust will get to the discs and calipers...

Again, than you for your ideas!
 

[RENNTAG]

Like what you are doing rex 

With regards to directing the air flow to the gains I agree with rex. I think that way it will cause a high pressure and accelerate the air out towards the veins. That's my understanding anyway.

[rich83]

Like what you are doing rex 

With regards to directing the air flow to the gains I agree with rex. I think that way it will cause a high pressure and accelerate the air out towards the veins. That's my understanding anyway.

It might make the air leave the pipe quicker but it will reduce volume of air flowing out the end. Which ones most important?

[rex]

Thank you very much for your thoughts guys! 

IMO, the more air I can get into the rotor vanes and/or in the disc bell, the better. I think that directing the air away from a disc face ans into the disc bell and/or vanes makes a lot of sense. In the pictures above you will see a couple of examples...
IMO, no matter how the air gets there, the main idea it has to go out, and I will go out, mostly, through the rotor vanes thus cooling the rotor.

[the bruce]

Yes, the area where the air exists is smaller, but the same amount of air travels through there.
Because the exist is smaller than the intake, the air will travel faster through the exist.

Unfortunately it will not be the same amount, Vlad.  

I am not sure this way really solves what I want to do... I want to direct the air towards the disc vanes / disc bell and NOT directly on the inner side of the disc.

Yes, of course. Directing the air flow into the bell is your major target, but the 2nd
one will be to get much air in as possible and even more so if you keep the shields
which inhibit the cooling of the rotors inner face.
That's why I suggested it that way keeping the full amount of air flow.

I agree, but the only reason to keep the dust/mud guard (shield) is that my car is is still a daily drive and a lot of dirt/dust will get to the discs and calipers...

I know. You won't need the shields in the summertime though. The better way would
be to remove them in the summertime (when your tracking) and fit them in the winter
if you feel a need. I didn't even miss them in the winter (you might know there's lots
of salt on German Autobahn).

It might make the air leave the pipe quicker but it will reduce volume of air flowing out the end. Which ones most important?

Agree. That's been my consideration. The air will accelerate at the narrow area, but
drag will increase at the same time (according to Bernoulli and Newton - continuity of
momentum). As a consequence there must be less volume in the end.

IMO, the more air I can get into the rotor vanes and/or in the disc bell, the better.

That's indeed the point. I'm pretty sure with deflectors similar to what I suggested
you will get at least the same amount of air into the bell as you get with the one
you proposed (I believe even more). The 2nd benefit would be the disc face also
gets some air.
Keep in mind if you keep the shields the inner face of the rotor will get hotter than
the outer face causing 'shielding' or even warping.
At higher temps in the 500° C area heat radiation plays a major role compared to
lower temps. With a dust shield on one side the disc will not just get hotter, it will
also have a very unequally temperature distribution.

[DaveB@Vagbremtechnic]

Some good work Rex, I can't help but think after enjoying your videos that you've outgrown the NQS kit and should maybe buy an AP offering.

Some thoughts....

Standard discs are straight vaned and not directional and curved.....this means they will distribute any air that's introduced in that area but they are ineffective at creating a low pressure area behind the disc to encourage flow....they blow but don't suck simply put

THIS WILL BE THE BIGGEST ISSUE....some directional discs without ducting will work similarly to straight vane discs with ducting

ANY cooling even the wheel arch mod is better than none

Any air introduced should ideally find itself behind the hub area only, only cool the back ace directly if you ave front face cooling too this can be via a device on the wheel or via vents milled onto the back of the bell which line up with the rotor vents

Ditch the dust shields

Regarding ducting I tried every which way to get the phaeton ducts to work, I ended up grinding that much of them away they didn't resemble ducts anymore. John from rally tech near us then decided to take pity on me after having a laugh at my creative skills and suggested a scoop/shield idea straight from the WRC cars that he does all the carbon for.

They've moved away from ducting generally and started using scoops, they're lighter and less complicated.

So i find myself with a 2011 TTRS front subframe complete down the side of my house which growls at me every time I walk my dog because I haven't done anything with it for three month, plan is to develop an integrated scoop/shield in carbon that's simple to bolt on ........problem is Rex it can only work from about 330-390mm rotor size.

I wouldn't worry too much about the volume of air and Mr Bernoulli this isn't Formula 1 and if it got to that stage where he featured then the pads would have given up 2 miles ago and all the rubber seals on the Calipers would have melted.

There also doesn't seem to be much point in doing anything complex to straight vane discs.....its like spending a fortune on developing a turbo for a 650cc engine when you can just drop in a 2.0 and go,just as fast......when you turbo (duct) the 2.0 engine (directional rotors) is when you will see the results....make sense?

AP have some great pics of their GT and LMP ducting recommendations COMPLETELY impractical on a road car but they steer the thought process I'll try to,post them up

[DaveB@Vagbremtechnic]

From AP

A good source of cooling air should be supplied preferably through the upright to the disc throat. A typical venting cross section of 100cm² (16in²) is usually sufficient. The pick up should preferably be in an area of clean high pressure air flow and the ducting should be arranged to avoid sharp bends or changes in section which may choke the air flow.

Careful design of the Mounting Bell is important in achieving effective disc cooling and avoiding problems. Typically 80% of the airflow should be directed up the disc vents and 10% up each face of the disc. This ratio can vary considerably in practice but it is important that both disc faces are cooled equally by adjusting the air gaps. Unequal face temperatures can lead to disc distortion and a long pedal. 
Lightening holes in the bells should be avoided as available cooling air can be lost without cooling the disc.

I'll find some more....

[rex]

Thank you very much guys for your information and implication!  

There are some interesting thoughts...
1. Dust shields...
Holger, I know you always said to ditch the dust shield and for performance you are 100% right!
a. As far as I know, it is impossible to take the dust shields off the car without taking the disc down (and the caliper). Although this is not a complicated operation I prefer not to take the calipers off the car 2 times per year.
b. The dust shield also provide a good base for mounting the air inlet. Without them I would need to create a bracket to fix the air inlet.
c. The problem with the dust/dirt. In the pictures above you can see the dust/dirt accumulated on the dust shield. Wouldn't it be a problem if all this dirt entered the caliper pistons?
I will look into these problems closely too see if there are simple solutions.
I want to buy a dust shield today to have the hub assembly complete and see if I can solve point a.

2. Buying a new brake assembly (like AP).
Unfortunately my finances are very low and the nqsbbk is very very close to being perfect for my car. Please remember I only have 160bhp and down Hungaroring straight I reach 170kph apposed to fuscobal's 210kph (I think). I abuse the brakes (aka braking like I should) for 7-8 laps at a time and, only after 3-4 rounds, the pedal gets softer. This is why I want to improve the brakes slightly and I do not expect miracles from the brake ducts. Dave, from what you said, I understand that any cooling is good and that I should expect at least some improvement. Did I understand correctly?
Also the nqsbbk fits behind 16 inch rims that no bbk does (for the mk5), relatively cheap discs, pads and maintenance. So, if I can improve the brake fade slightly there are no reasons to go for AP.

3. Having directional vanes or not...

some directional discs without ducting will work similarly to straight vane discs with ducting

This means that ducting is doing something good for the OEM 312 discs...
By the way Dave, did you create that 315x25 AP rotor for the nqsbbk kit?

4. These ducts with other BBK...
Am I correct into thinking that the brake ducts as described above are useful for any BBK (AP PRO 5000 for example)? The way I "designed" these brake ducts they will fit the 312 rotor but can be fitted to any other rotor larger than this.
So if I create these brake ducts I can change the BBK and not have to start from scratch...

5. For street/winter use I intend to "disable" the brake ducts. There are 2 ways:
a. put something over the brake duct intake (from the fog grille).
b. put something to block the air next to the hub.
I am not sure which way I will go but, I hope I can created a cover for point a. Please keep in mind that I want the solution to be nice and tidy and I want to make it flexible so that I can take it off/ put it on in less then 5 minutes.

P.S. About making something complicated, I have some time to kill... And I also find it very rewarding actually doing something by myself for the car and not buying parts.
Any more thoughts/suggestions are welcomed and, again, than you guys very much for your implication so far!

[the bruce]

First of all, I agree with Dave. I remember reading AP's advice on brake ducting some
time ago. Of course Bernoulli's principle still applies to fluid dynamics, even in F1.

Thank you very much guys for your information and implication! 

There are some interesting thoughts...
1. Dust shields...
Holger, I know you always said to ditch the dust shield and for performance you are 100% right!
a. As far as I know, it is impossible to take the dust shields off the car without taking the disc down (and the caliper). Although this is not a complicated operation I prefer not to take the calipers off the car 2 times per year.
b. The dust shield also provide a good base for mounting the air inlet. Without them I would need to create a bracket to fix the air inlet.
c. The problem with the dust/dirt. In the pictures above you can see the dust/dirt accumulated on the dust shield. Wouldn't it be a problem if all this dirt entered the caliper pistons?
I will look into these problems closely too see if there are simple solutions.
I want to buy a dust shield today to have the hub assembly complete and see if I can solve point a.

a) Right, you'd need to remove the caliper first, then the disc.
b) Yes, indeed. That's why I suggested cutting the shield to a minimum to just being
 a kind of 'bracket' for the duct.
c) Guess not.

I'd give you my old dust shields for free. I shurely will never refit them. Shipping will
exceed the cost of new shields though.

2. Buying a new brake assembly (like AP).
Unfortunately my finances are very low and the nqsbbk is very very close to being perfect for my car. Please remember I only have 160bhp and down Hungaroring straight I reach 170kph apposed to fuscobal's 210kph (I think). I abuse the brakes (aka braking like I should) for 7-8 laps at a time and, only after 3-4 rounds, the pedal gets softer. This is why I want to improve the brakes slightly and I do not expect miracles from the brake ducts. Dave, from what you said, I understand that any cooling is good and that I should expect at least some improvement. Did I understand correctly?
Also the nqsbbk fits behind 16 inch rims that no bbk does (for the mk5), relatively cheap discs, pads and maintenance. So, if I can improve the brake fade slightly there are no reasons to go for AP.

No doubt - ANY cooling is good. It's hard to tell specific numbers, but as a ball-park figure
I'd expect 50° C lower peak temperatures with proper cooling and a similar amount with
directional rotors.
The softer pedal may come from both fluid boiling and rotor distortion by some amount.
Again, the dust shield prevents the inner face of the rotor from being cooled equally to the
outer face.
A cooler running rotor will also cool the pad better and heat up both caliper and fluid less.

3. Having directional vanes or not...

some directional discs without ducting will work similarly to straight vane discs with ducting

This means that ducting is doing something good for the OEM 312 discs...
By the way Dave, did you, create that 315x25 AP rotor for the nqsbbk kit?

From what I remember Performance Friction made a small number of 312x25 discs for AWE.
Sadly they stopped making them. AP Racing still makes a "Strap Drive" kit for R32 & S3:

http://www.apracing.com/product_details/road_car_upgrades/oe_replacement_disc_kits/strap_drive_kits_and_system/vw_golf_mk5.aspx

4. These ducts with other BBK...
Am I correct into thinking that the brake ducts as described above are useful for any BBK (AP PRO 5000 for example)? The way I "designed" these brake ducts they will fit the 312 rotor but can be fitted to any other rotor larger than this.
So if I create these brake ducts I can change the BBK and not have to start from scratch...

Certainly it'll help with any BBK. Very large BBKs may even make it easier to fit a duct
between hub and caliper instead of the back side of the hub.

5. For street/winter use I intend to "disable" the brake ducts. There are 2 ways:
a. put something over the brake duct intake (from the fog grille).
b. put something to block the air next to the hub.
I am not sure which way I will go but, I hope I can created a cover for point a. Please keep in mind that I want the solution to be nice and tidy and I want to make it flexible so that I can take it off/ put it on in less then 5 minutes.

To me a) seems to be most practical. I even guess blowing some clean air to the rotor
may help to keep it free from salt and water. Keep in mind it's the tyre swirling up
water and salt.

P.S. About making something complicated, I have some time to kill... And I also find it very rewarding actually doing something by myself for the car and not buying parts.
Any more thoughts/suggestions are welcomed and, again, than you guys very much for your implication so far!

I guess we already covered most of the theme. Ducting is good, ducting + directional rotors
is better and a properly vented BBK is best. Now you know how to design the ducts correctly,
but however you do it - it will help lowering rotor (and pad + caliper) temperatures.

It's all right as long as you do any venting.


BTW,
Vlad consider to get some downforce as Fuscobal does. Your car will run slower on the straight
and faster on the corners. >> Less brake effort, less heat. 

[rex]

Yup, I guess you summarized it correctly!

I already bought a new dust shield... It will arrive tomorrow... It was about 10 EURO (~8 GBP) and I had 50% discount so it was not worth to get it from other places... Thanks for the thought, though!
I will have it fitted tomorrow and see how it goes from there on.

OFFTOPIC.
Yes, I told fuscobal to keep the templates so it will be easier to have a wing mounted later on.
I also want to have a rear diffuser but this is a costly job since I want to change the whole exhaust with the new diffuser.
But both these chapters require spending money and I prefer to spend the money on going to Hungaroring and/or Nurburgring instead. There is enough time to do all the mods...
So, since the finances are limited I want to do these brake vents and also a baffled sump.

[fuscobal]

Very nice topic Rex. I see 2 problems there :

1) There will be like 2 shims (plates) in the front grille right in front of the entrance to the duct. I don't know what they'll do to the air entering the duct (regarding speed and turbulence)
2) Having the diameter of the duct shrink just before the exit to the disc will accelerate air while the exact opposite should be done (at least that's how it works for the radiators). Don't know how this will interact with the disc's rotation and the cooling vanes. For a radiator, you'd want the air to slow down before hiting it. In Simon McBeath's book there were some comparisons with various guides in front of the radiators if I recall correctly ! Can't you try to make an ovaloid section there (like 2cm high and 10cm long or whatever gives an area larger than your 5cm diameter duct). Ap said "A typical venting cross section of 100cm² (16in²) is usually sufficient. The pick up should preferably be in an area of clean high pressure air flow and the ducting should be arranged to avoid sharp bends or changes in section which may choke the air flow". High pressure airflow equals low speed, meaning you'll have to enlarge the exit, not shrink it. Going even further, 100cm² is way more than what your 5cm duct gives you (19.6cm²)

If I were you, I'd use the brakes as they are but without the shields (my APs are not that dirty and remember I have no seals on my calipers) and I'd upgrade to some medium brake kit like 4 pots with 320-330mm sometime when possible !

[rex]

Thank you for your thoughts, fuscobal  !

Well, those 2 points are problems only if the goal is to create the perfect brake ducts performance wise! So, great advice for anyone who will build some brake vents and want maximum performance!
But, I am aware that I want to make some esthetic and daily drive mods...
So those 2 problems are not quite problems as far as I am concern:
1. Yes, those 2 plates might affect the air flow but I also want my car to look OEM (OEMish) and nice. So they will stay on...
2. With the OEM 312mm discs there is not enough room to expend the exit. Restricting the air flow was done only because I had to redirect the air towards the disc bell (hub). If I had had enough space to make another exit I would have done it. For larger diameter rotors (like yours) the exist can be made differently (with a larger exit)....

[the bruce]

If I were you, I'd use the brakes as they are but without the shields (my APs are not that dirty and remember I have no seals on my calipers)....

Vlad, you see we won't stop forcing you to discard them.   

Your brakes will welcome the absence of these needless shields.*

 


* of course in this specific case you'd best cut them to a minimum able to provide fitment of the ducts

[rex]

  We have a saying: "When everybody says you're drunk, it's time to go to bed"   (since everybody is telling me to drop the dust shields  )
I will install the shields for the template (Saturday or Sunday) and see how it goes from there on...