Background story: I bought a very abused E46 M3 last winter, and I've been trying to get it up and running as a dedicated track car (cooling system refresh, subframe reinforcement plates, all new bushings, etc). Track day #1 led showed overheating issues and led to a CSF triple pass radiator and SPAL electric fan. Track day #2 built confidence with the car but roasted brakes. By 'roasted' I mean 'warped rotors so badly after a few sessions that I had to replace the rotors instead of eating lunch'...
So my next step was to introduce a brake cooling duct system. I almost pulled the trigger on the brake ducting kit from bimmerworld, but before spending $300+ on parts, I wanted to make sure there wasn't another solution. Plus, I wasn't 100% sure that cooling ducts would be the solution to my problem - I experienced brake judder, not pad fade - so I decided to do a temporary mock up to make sure my overheating problem was diagnosed correctly.
PLEASE NOTE (Disclaimer): This was NOT intended to be a permanent solution, but rather a cheap intermediary setup to test the performance of brake cooling ducts before doing a complete install. Do not follow these instructions and expect a flawless and reliable ducting system. This is not nearly as legit as the bimmerworld (BW) or comparable kit. Brake cooling performance may be notably improved from stock but is definitely less than the tried-and-true method. I make absolutely no guarantees about this setup.
Enough rambling, let’s get to the good stuff… (I apologize in advance for missing some of the important pictures, as they were all taken at the end as an afterthought)
This write up was done on a 2003 M3 (pre-facelift) with stock foglights + air intakes. The problem is that the stock air intakes direct air at your tire, not to the inside of your rotor, where it desperately needs fresh air. If you’ve already looked into brake ducts, feel free to skip ahead to step # 10 - this is probably the most useful thing you can get out of my writeup…
What you will need:
2-4 hours of free time (took me 3.5 hours including time to mock up different routing and get the gonads to start cutting parts)
3” brake ducting - I think I used a 3.5 foot section on each side. Probably a little less, but I didn’t take final measurements.
“Measure twice, cut once” mindset
Jack / stands / etc
Standard mechanics tool set for part removal
Tin snips
Hacksaw, cutting wheel or other cutting tool (for cutting existing plastic inlets)
Safety wire (at least 25’)
Zip ties
Paint marker
1. Jack up car. (SAFELY!!)
2. Remove front wheels.
3. Remove plastic wheel liners
4. Remove front splash shield
5. Remove right and left air guides next to the foglights. The two clips holding these against the aluminum support bracket were quite difficult to remove. Good luck.
6. Let’s start from the front… Your stock air inlets do a pretty good job of capturing the air, you just need to re-direct it into the ducting. The left hand side duct has a convenient knob on the side of it, which seems to fit perfectly for a 3” duct. (coincidence? maybe not) All you need to do on this side is lop off the rounded end and call it a day. The hose slips onto this shape nicely.
![Image]()
![Image]()
The right hand side is a little more complicated. The aluminum support bracket has a slightly smaller hole on this side, so you’ll need to flatten your duct to fit through it. I ended up with a relatively flat and very wide duct on this side. Mark the perimeter of the plastic duct where your tubing will go, and cut carefully. If in doubt, start by cutting a smaller area out, then enlarge it to fit. My tube was tight on this side so that I didn’t use any fasteners to keep it in place - it was a nice press fit.
![Image]()
7. Once both of these parts are cut, close off the rectangular opening on the back of this duct (I used duct tape, but I’m not thrilled with it). Put the parts back in the car and fit your hose to them.
Note: This method is definitely not as ideal as the other solutions out there, as you will inevitably lose efficiency due to the indirect airflow path. Again, this is just for temporary purposes, so any die-hard track driver will need to go a different route. I have experience in a Miata in HPDE 4, so I consider myself to be pretty aggressive but I don’t claim to be a great driver, especially in an M3.
![Image]()
8. The next part is pretty straight forward. You’re trying to get the ducts from point A to point B. Route them back from the inlets to the sway bar, then turn and go along and above the tie rod to the opening in the brake dust shield. I tried a few different routing options (trying to snake between all the suspension / steering geometry) with no success. It may look promising with wheels in the air, but when you load the suspension, the hose gets pinched. The only way to keep your hose from being crushed or rubbing too badly on surrounding parts is to go underneath the sway bar and forward of the tie rod. Use beefy zip ties or large worm drives to secure.
Note: I’m aware that the hose can rotate around the tie rod and become pinched between this and the sway bar. After two track days and regular street use, this has not happened to me but I must stress that this is one of the weak points of this hose routing without a BW flange.
![Image]()
![Image]()
9. The center splash shield needs to be modified before re-installation. If you are planning to get flanges at some point, this is a good time to cut the 3” diameter hole for those. That would help reduce chances of getting your hose pinched between the sway bar and tie rod. In my case, my splash shield was severely cracked on one side already, so I chopped off the two vertical wings and left it at that. The hose fit through this area nicely, although my “chop-it-off” solution opens up the side wall which could allow more air to escape, affecting engine cooling and fuel economy. (as if you care about fuel economy!) Just forewarning - ultimately you should only do what you are comfortable with.
![Image]()
10. Let’s finish with the most tedious part, which is building the attachment structure for the ducts to keep them snugly against the brake rotor. The problem here is that there’s really nothing good to tie to for securing the ends of the ducts, short of getting the BW backing plates. My solution was to make three different tie downs - one main tie for the duct itself, and one above and one below the duct around the knuckle to act as attachment for the main one. The first step is to locate the hole in your brake dust shield just forward of the wheel center axis. This is your duct inlet location - no modifications necessary to the dust shield for our purposes.
I started by mocking up the attachment with zip ties (unless you have some magic high-temp zip ties, I recommend you only use these for mockup purposes). The main zip tie will go around the brake duct, and attach to the other two zip ties. Here’s the image of my final setup, just so you know what I’m getting at. Without the other two mount points, there’s no way to keep the duct exactly where you want it.
![Image]()
The upper attachment piece goes around the upper center portion of your knuckle. Tighten down to a loose fit so it stays in place.
![Image]()
The lower zip tie goes directly below the hole, again on the knuckle.
![Image]()
11. Now we need to set the right length for your hose. With the front end in the air, and your key to IG2 (to disable steering lock), you can turn the knuckle by hand. This is the part that needs your best judgment - set it so that you can turn the wheel lock to lock without any rubbing on important parts, or uncomfortable straining of the hose. Leave a little extra hose length (2” extended) at the end. Measure twice, then cut to length. I suggest removing sections of the hose in increments just to be safe.
You will now need to re-shape the end of your hose to match the kidney shape of our inlet. This is relatively easy - push one side in until it fits nicely against the knuckle. Add the main tie around the brake duct and tighten it all up.
![Image]()
12. Once you’re comfortable with your mockup, then you are ready to replace the zip ties with something that can handle the heat. I used a length of safety wire (conveniently one 25 foot long coil was perfect length for this project). After the first two attempts where I tightened down too much and snapped the safety wire, I decided to braid four strands together for a stronger attachment. Few people have safety wire pliers, which makes this process a lot easier, but twisting them by hand isn’t too bad if you have two sets of vise-grip pliers. (hint: if you don’t have any friends to help, you can stand on one end)
Once you have a right / left set of perfectly braided wires, start replacing the zip ties and tighten everything down. I left about 5-7 coils of the internal hose support wire between the dust shield and the safety wire attachment. (reference above image) This provides some pre-load against the dust shield to keep the hose in place.
13. Make sure the rest of your zip ties are secure, turn the rack from lock to lock one last time to double check, re-tighten your attachment, and start putting everything back together.
![Image]()
Next step: I went to Lowes and found some black gutter mesh. Looks to be about the right height, so I’m going to install this before my next event. This is primarily to keep debris out now that there is no longer a hole in the back to allow rocks to fall out.
I’m probably going to leave these on my car indefinitely, or at least until next season when I have more time to correctly put the ducts in permanently. After a two-day event at Mid Ohio, I haven’t noticed any downside to the routing of these ducts, so I’m not worried about any short term durability issues except the aforementioned debris concern.
This writeup is intended to guide someone that’s running out of time to order the bimmerworld kit before an event and just needs a quick solution. This solution is littered with inefficiencies, so take it for what it’s worth. Hope it helps.
- Brian
So my next step was to introduce a brake cooling duct system. I almost pulled the trigger on the brake ducting kit from bimmerworld, but before spending $300+ on parts, I wanted to make sure there wasn't another solution. Plus, I wasn't 100% sure that cooling ducts would be the solution to my problem - I experienced brake judder, not pad fade - so I decided to do a temporary mock up to make sure my overheating problem was diagnosed correctly.
PLEASE NOTE (Disclaimer): This was NOT intended to be a permanent solution, but rather a cheap intermediary setup to test the performance of brake cooling ducts before doing a complete install. Do not follow these instructions and expect a flawless and reliable ducting system. This is not nearly as legit as the bimmerworld (BW) or comparable kit. Brake cooling performance may be notably improved from stock but is definitely less than the tried-and-true method. I make absolutely no guarantees about this setup.
Enough rambling, let’s get to the good stuff… (I apologize in advance for missing some of the important pictures, as they were all taken at the end as an afterthought)
This write up was done on a 2003 M3 (pre-facelift) with stock foglights + air intakes. The problem is that the stock air intakes direct air at your tire, not to the inside of your rotor, where it desperately needs fresh air. If you’ve already looked into brake ducts, feel free to skip ahead to step # 10 - this is probably the most useful thing you can get out of my writeup…
What you will need:
2-4 hours of free time (took me 3.5 hours including time to mock up different routing and get the gonads to start cutting parts)
3” brake ducting - I think I used a 3.5 foot section on each side. Probably a little less, but I didn’t take final measurements.
“Measure twice, cut once” mindset
Jack / stands / etc
Standard mechanics tool set for part removal
Tin snips
Hacksaw, cutting wheel or other cutting tool (for cutting existing plastic inlets)
Safety wire (at least 25’)
Zip ties
Paint marker
1. Jack up car. (SAFELY!!)
2. Remove front wheels.
3. Remove plastic wheel liners
4. Remove front splash shield
5. Remove right and left air guides next to the foglights. The two clips holding these against the aluminum support bracket were quite difficult to remove. Good luck.
6. Let’s start from the front… Your stock air inlets do a pretty good job of capturing the air, you just need to re-direct it into the ducting. The left hand side duct has a convenient knob on the side of it, which seems to fit perfectly for a 3” duct. (coincidence? maybe not) All you need to do on this side is lop off the rounded end and call it a day. The hose slips onto this shape nicely.
The right hand side is a little more complicated. The aluminum support bracket has a slightly smaller hole on this side, so you’ll need to flatten your duct to fit through it. I ended up with a relatively flat and very wide duct on this side. Mark the perimeter of the plastic duct where your tubing will go, and cut carefully. If in doubt, start by cutting a smaller area out, then enlarge it to fit. My tube was tight on this side so that I didn’t use any fasteners to keep it in place - it was a nice press fit.
7. Once both of these parts are cut, close off the rectangular opening on the back of this duct (I used duct tape, but I’m not thrilled with it). Put the parts back in the car and fit your hose to them.
Note: This method is definitely not as ideal as the other solutions out there, as you will inevitably lose efficiency due to the indirect airflow path. Again, this is just for temporary purposes, so any die-hard track driver will need to go a different route. I have experience in a Miata in HPDE 4, so I consider myself to be pretty aggressive but I don’t claim to be a great driver, especially in an M3.
8. The next part is pretty straight forward. You’re trying to get the ducts from point A to point B. Route them back from the inlets to the sway bar, then turn and go along and above the tie rod to the opening in the brake dust shield. I tried a few different routing options (trying to snake between all the suspension / steering geometry) with no success. It may look promising with wheels in the air, but when you load the suspension, the hose gets pinched. The only way to keep your hose from being crushed or rubbing too badly on surrounding parts is to go underneath the sway bar and forward of the tie rod. Use beefy zip ties or large worm drives to secure.
Note: I’m aware that the hose can rotate around the tie rod and become pinched between this and the sway bar. After two track days and regular street use, this has not happened to me but I must stress that this is one of the weak points of this hose routing without a BW flange.
9. The center splash shield needs to be modified before re-installation. If you are planning to get flanges at some point, this is a good time to cut the 3” diameter hole for those. That would help reduce chances of getting your hose pinched between the sway bar and tie rod. In my case, my splash shield was severely cracked on one side already, so I chopped off the two vertical wings and left it at that. The hose fit through this area nicely, although my “chop-it-off” solution opens up the side wall which could allow more air to escape, affecting engine cooling and fuel economy. (as if you care about fuel economy!) Just forewarning - ultimately you should only do what you are comfortable with.
10. Let’s finish with the most tedious part, which is building the attachment structure for the ducts to keep them snugly against the brake rotor. The problem here is that there’s really nothing good to tie to for securing the ends of the ducts, short of getting the BW backing plates. My solution was to make three different tie downs - one main tie for the duct itself, and one above and one below the duct around the knuckle to act as attachment for the main one. The first step is to locate the hole in your brake dust shield just forward of the wheel center axis. This is your duct inlet location - no modifications necessary to the dust shield for our purposes.
I started by mocking up the attachment with zip ties (unless you have some magic high-temp zip ties, I recommend you only use these for mockup purposes). The main zip tie will go around the brake duct, and attach to the other two zip ties. Here’s the image of my final setup, just so you know what I’m getting at. Without the other two mount points, there’s no way to keep the duct exactly where you want it.
The upper attachment piece goes around the upper center portion of your knuckle. Tighten down to a loose fit so it stays in place.
The lower zip tie goes directly below the hole, again on the knuckle.
11. Now we need to set the right length for your hose. With the front end in the air, and your key to IG2 (to disable steering lock), you can turn the knuckle by hand. This is the part that needs your best judgment - set it so that you can turn the wheel lock to lock without any rubbing on important parts, or uncomfortable straining of the hose. Leave a little extra hose length (2” extended) at the end. Measure twice, then cut to length. I suggest removing sections of the hose in increments just to be safe.
You will now need to re-shape the end of your hose to match the kidney shape of our inlet. This is relatively easy - push one side in until it fits nicely against the knuckle. Add the main tie around the brake duct and tighten it all up.
12. Once you’re comfortable with your mockup, then you are ready to replace the zip ties with something that can handle the heat. I used a length of safety wire (conveniently one 25 foot long coil was perfect length for this project). After the first two attempts where I tightened down too much and snapped the safety wire, I decided to braid four strands together for a stronger attachment. Few people have safety wire pliers, which makes this process a lot easier, but twisting them by hand isn’t too bad if you have two sets of vise-grip pliers. (hint: if you don’t have any friends to help, you can stand on one end)
Once you have a right / left set of perfectly braided wires, start replacing the zip ties and tighten everything down. I left about 5-7 coils of the internal hose support wire between the dust shield and the safety wire attachment. (reference above image) This provides some pre-load against the dust shield to keep the hose in place.
13. Make sure the rest of your zip ties are secure, turn the rack from lock to lock one last time to double check, re-tighten your attachment, and start putting everything back together.
Next step: I went to Lowes and found some black gutter mesh. Looks to be about the right height, so I’m going to install this before my next event. This is primarily to keep debris out now that there is no longer a hole in the back to allow rocks to fall out.
I’m probably going to leave these on my car indefinitely, or at least until next season when I have more time to correctly put the ducts in permanently. After a two-day event at Mid Ohio, I haven’t noticed any downside to the routing of these ducts, so I’m not worried about any short term durability issues except the aforementioned debris concern.
This writeup is intended to guide someone that’s running out of time to order the bimmerworld kit before an event and just needs a quick solution. This solution is littered with inefficiencies, so take it for what it’s worth. Hope it helps.
- Brian
