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I've been concerned for a little while over my brake temperatures on track days, the increased wear of the inner brake pads and the fast wear after the pads get to 1/3 thickness. I therefore had a look at ways that I could get brake cooling without spending a fortune. The more I looked at what other people had done on other cars, eg here and here, the more I wanted to use my experience and knowledge of aerodynamics rather than just cobble something together. They are both easier and cheaper than my project, but they are too inefficient and agricultural for me (I was spoilt by doing an aeronautically-biased engineering degree, doing an Aeronautical Systems Masters and working with Germans for 7 years in which everything I did had to be spot on).
Why bother with aerodynamics? Apart from my finding the subject fascinating, a poor system design can increase drag significantly. Cooling systems and front wheels account for some 35% and 13% respectively of total drag; taking clean air from the bumper, throwing it or fitting big tubes into the front wheel wells can make this situation far worse.
I’m doing this in the first instance on my R3 then on my S1 project car. The main differences between the 2 that affect this are the fog lights and how the radiator inlets are configured.
I began by breaking the problem into 2 parts: where to get cooling air and how to take it to the brakes. The second question has 2 possible answers: to duct it to the centre of the brake discs directly or to angle air across the wheel wells towards the brake discs. Whilst large hoses in the wheel wells can cause some drag (think of all that rotating air hitting the hoses), throwing air into the wheel wells will almost certainly cause much more drag.
The air flows and pressures inside and adjacent to a wheel well are complicated and dependent on such factors as the shape of the wheel. You can get some unexpected results; for example, Vauxhall found that when they extended the bumper of the Calibra (class-leading CD of 0.29) downwards the air exiting the wheels interfered with the air coming off the air dam produced more drag rather than less as had been expected.
I looked at 4 ways of getting cooling air: a hole in the bumper or radiator air inlet, a scoop under the undertray, a scoop attached to the wheel hub and a hole just forward of the front wheel air dams (the short blades that come down from the undertray just in front of the front wheels). I don’t like the idea of taking air from the bumper that would otherwise pass down the side of the car with relatively low drag, but it is the simplest and somewhat obvious. I ruled out scoops under the undertray (too much drag, reduced ground clearance, risk of damage) and on the hub (hard to get cooling air without restricting steering movement), so that left only taking air from in front of the air dams.
What are the air dams for, you may ask, and how can they get cooling air? They’re there to trip underbody air before the front wheels and so reduce interference with the air from the front wheels; when designed correctly they reduce drag by around 4%, albeit the increased pressure they generate causes lift. If I place the inlet just in front of the air dams then the increased pressure will drive air through a hose to the brake discs, thus reducing the air left to cause drag at the wheels and further along the underbody.
To measure the static air pressure for both these choices I carried out a DIY pressure check with some differential pressure gauges connected to plastic tubing run to 3 places: the number plate (for stagnation pressure), the air dams and the centre of the brake disc. The pictures show the gauges and the tubing going to the brake disc.
Compared to atmospheric, the pressure in the brake disc was slightly lower below 50 mph and slightly higher above, and the pressure difference at the air dams was 70-75% of the pressure difference at the number plate (approximately stagnation pressure).
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Calculating the size of the hose is so complicated that I took the easy route of seeing what others had claimed for their projects and scaling accordingly. This gave me a diameter of 40-50 mm and the available space at the brake discs made 50 mm (2”) the best size to start with.
When I look to route the hoses I’ll look to leave room for modding the oil cooler exhausts later on. The oil coolers vent into the wheel wells immediately ahead of the tyres, with Mazda making an attempt to angle the outflow downwards to minimize drag with the air rotating around the tyres. Mazda's design shows all the compromises for space, complexity and cost inherent in any road car and, IMO, have done a reasonable job, notably having inlet ducting. That said, the design is far from the ideal (radiators are most efficient when they have inlet and exhaust ducting with an inlet/outlet 1/4 of the radiator width at 1 width ahead/behind the radiator) and I have a project on my list to assess making cooling more efficient by fitting exhaust ducting to my project car (IMO the design is perfectly adequate for standard cars, to the extent that blanking is needed for cold weather). For completeness, I’ll mention that I’ve considered a few other improvements around the wheels: vents in the top of the wings (too flash); vents in the rear of the well (too much work?); aerodynamic fairings in front of the wheels as in Merc SLRs (too much trial-and-error effort to avoid stability problems); and fairings on the wheels (looks a bit silly). Sucking air out of the rear wheel wells and venting it out the rear bumper using an electric fan will significantly reduce drag, say by 8%, mainly by filling in the low pressure area at the car rear.
I’ve now ordered the bits I need and will update this thread when I’ve got more to show.
Sounds like a fun project! I'm looking forward to the rest of your write up.
Off topic, but since you were talking about aerodynamics did you know that the side fender vents are functional? The old debate was that they couldn't be functional because there was no direct path to the engine bay for cooling, which is true, but people seem to have overlooked the one place that they have a direct connection to. The fender vents are ducted directly to the bottom of the windshield! It's a modestly sized duct and one of is purposes is to drain water from the windshield, but it's big enough to significantly reduce the ultra high pressure zone that's common at hood-windscreen transitions.
I'll have a look at threads later. My view is that the ducts are mainly styling and do little. There is a small rectangular hole in the engine bay side that vents into the wing and then, presumably, out the ducts. Any air exiting would be pretty turbulent and I cant see it doing much in practice. The ducts on the R3 are far smaller and will do nothing. I can't see any vent to the windscreen and, in any case, the air at the base of the windscreen probably adds more in downforce than it adds in drag.
Here is my write up of fitting track day brake cooling to my R3. I’m fitting 2 alternative sources for the cooling air, one on the undertray just in front of the wheel spoilers and one in the radiator inlet, with the intention of investigating performance on my next track day (02 December 2014).
What I used:
• Jacks, axle stands and wheel brace.
• 14mm & 17mm spanners for brake bolts, impact driver for brake disc bolts, mini hacksaw & pliers or jig saw or hole cutter for cutting shields, 2” (51mm) hole cutter, drill & drill bits, pop riveter & rivets (I used 4mm diameter rivets) or small bolts & nuts, torque wrench, screwdrivers.
• 4 x Revotec 2” inlet/outlet flange, 2 x 1m Neoprene 2” (51mm) ducting hose, 4 x Revotec 2” (51mm) wire clips or 40-55mm Jubilee Clips, 6 x Jubilee Clips 55-70mm, 12” 2” plastic pipe. I also used some aluminium hose joiners that I had spare to protect the hose.
Process:
1. Loosen wheel bolts, jack up the car front onto axle stands, remove the front wheels, remove the front brakes (2 x 14mm & 2 x 17 mm bolts), remove the brake discs (you may need an impact driver for the disc bolts) and remove the front wheel well fairings.
2. Bend the shield angled leading edges flat.
3. Mark a 51mm hole for the inlet/outlet flange on each shield just forward of the hub concave leading side, leaving a gap of 3-4 mm to the hub for the thickness of hose. Using whatever method suits (hacksaw & pliers to bend/shear metal, jigsaw or hole saw) cut the holes for each inlet/outlet flange.
4. Fit an inlet/outlet flange in each hole, drill holes for the securing rivets or bolts and rivet/bolt the flanges to the shields.
5. Fit one end of each hose over each flange and secure with a wire or Jubilee clip.
6. Secure the hose to the upper wishbone using Jubilee clips. I bent the Jubilee clips to grip the wishbone and used aluminium hose joiners to protect the hose.
7. Adjust the length of the hose so that it coils smoothly from full left lock to full right lock (see photos).
8. For the radiator inlet intake, cut a 6” length of 2” plastic pipe, drill or cut a 2” (51mm) hole facing forward into the angle intake side, fit the pipe in, drill mounting holes for a Jubilee clip, fit a Jubilee clip to hold the pipe and fit the hose end with a wire or Jubilee clip.
9. For the undertray intake, cut a 2” (51mm) hole for an inlet/outlet flange in each fairing, fit a flange in each, drill holes, secure the flange with rivets or bolts, smooth the edges of fairing and, if you want to, fill any gaps with sealant. I fitted one flange above the fairing and one below. Cut a hole in the edge for the hose to pass through (just visible in the R3 fairing picture). The pictures show an arrangement for S1 cars and for R3s (yes, the fairings are different, as I found out by first using spare S1 fairings for my R3).
More to follow when I do it.
All going well I should have some test results on Tuesday.
A final few installation notes:
I put the hose on the undertray inlet, fitted an end-cap to the radiator inlet pipe, refitted the fairing, used a Jubilee clip to secure the hose to the anti-roll bar to keep the hose clear of the tyre and added a plate to the shield. I’ll reinforce the hose around the ARB Jubilee clip after the track day.
I refitted the brake disc and brakes then manipulated the shape of the shield to remove any rubbing.
I did the offside (driver’s) side today, with 2 changes over the write up above.
Firstly, I secured the 3rd Jubilee clip to the wishbone rather than the ARB and added a protective sleeve of nylon webbing held on by some locking wire.
Secondly I relocated the wheel sensor lead to give me a little more clearance on full lock. This isn’t necessary as the arrangement above gives me a respectable 10mm between hose and the humongous rim protector on my 225/40/19 Bridgestone RE050s; however, I have some 19” 9J ET35 rims on which I may fit 265/35/19 tyres and I was intrigued to see what extra clearance I could get. I did this by relocating the wheel sensor leads and securing the hose to the wishbone rather than the anti-roll bar:
• I first removed the 12mm bolt for the lead’s wheel well bracket, bent the locating tab back and replaced the bracket and bolt so that the bracket ran above the hose rather than behind it as before.
• I then took the sensor lead out of the wheel hub bracket and used tie wraps (one plastic, one stainless steel) to fix the lead facing directly inwards.
• With the lead lined up along the wishbone, I fitted the 3 Jubilee clips securing the hose to run it along the top of the hose.
This gave me clearance of 20mm+.
Alas, the track day enabled only limited testing of the undertray inlet due to the weather, idiot drivers and the track staff taking almost 4 hours to clean dropped oil on 90% of the track and getting the OK to use it.
I too would like an update. I am still having problems dissipating excess heat from my brakes and am considering ducting the fronts. I like this method better than the other DIYs I have read, but I would love to see some empirical results.
looking at his two air scoop options I think first one (taking air from radiator shroud area) will yield significantly more flow to the brakes, making them cooler.
the second uptake location does not look as promising unless he attached proper scoop:
There are several good kits for Miatas, but the Sneed Speed one is the only once I can find for the 8. I'm not paying that much for a handful of cheap parts I can mostly source myself, and the inlets won't fit my Series 2 anyway. However, I might be willing to pay $75 for the wheel brackets alone--even thought I could make them myself for a few bones.
Before I go to modding and cutting, I need to know if ducting is viable for the 8, and whether I can do it without introducing much drag. In theory, I like the idea of using the positive pressure in front of the front air dams as a source of flow in the S2, but would like some results to review before I get started. Some ducting setups actually make cooling worse if they are not well-designed or well-implemented.
Alas. It is either ducting or spending the big $$ on a BBK. I don't need any extra stopping power, so the upgrade would be purely for added cooling.
Checking compatibility between NC and 8 parts is on my short list as I ponder this project. I thought they might be and intended to look into it.
Originally Posted by Nadrealista
I am thinking along the same lines. modify my existing brake shields or get the brackets for $75.
I would pick up air from the front ( radiator shroud) like spin9k and Ian did:
I don't really have a good way to do that from my Series 2 bumper that would be secure, attractive, and reversible. Taking advantage of positive pressure in front of the air dams looks like a great option--assuming it works.
there is positive pressure there for sure but I doubt that it will move enough air to cool the brakes. scoop or front mount is the only option I believe. but lets see what data Ian collects from his track day.
I am going to service my brakes tomorrow in preparation for another track day the following Saturday. I am planning to do some recon while I am in there to see if there is any other place where inlets can be secured.
I recently did a 2 day event in Spokane using 255 wide NT-01's, DTC-60 pads and Wilwood EXP 600 plus fluid and the front brake dust shields removed and had no fade whatsoever. I did get a soft pedal before using 550 degree Ford DOT3 fluid and the dust shields in place.
Originally Posted by stvnscott
I am still having problems dissipating excess heat from my brakes and am considering ducting the fronts..
I've got a set of Sneed ducts (hub side only) that it turns out I can't use since they'd interfere with my KW coilover reservoirs. They were never installed and I'm willing to part with them for a reasonable price. I've also got a length (6 foot?) of new hose and some shorter scraps, plus some scoops that I don't need that I can part with as well.
Originally Posted by stvnscott
Checking compatibility between NC and 8 parts is on my short list as I ponder this project. I thought they might be and intended to look into it.
RX8 hubs are a popular upgrade on heavily tracked NC's, as the RX8 parts are stronger, so the ducts should fit just fine, the only thing is that they're built for 2.5" hose whereas the Sneed ones are for 3" hose. RX8 Hub Upgrade For MX5 for MX5
Rather than duct the fronts now, I decided to adjust my braking habits and jump off the track and on to the highway for some additional cooling after the standard cool-down lap. One or both of those changes has helped tremendously. My brakes are a good 300-400 degrees cooler when I park the car. So, I'm going to fine tune my approach to braking to get my lap times back up to where they were and keep utilizing the highway for additional cooling for now.
You could also try what I did and get higher temp fluid and/or remove the dust shields behind the front rotors. The Wilwood EXP 600 plus has the highest rated boiling point of any racing fluid and it's near the bottom of the pack in terms of price, so I bought myself a 6 pack. The dust shields were easy to remove during a pad/rotor swap using a slide hammer.
11-21-2014, 01:18 PM
