c4 wheels and brake cooling
06-07-2014, 12:20 AM
#1
Burning Brakes
Thread Starter
c4 wheels and brake cooling
I will soon begin HPDE with 1993 C4, with Z07 package. I will have new Motul 600 or better brake fluid, new brakes and rotors, braided ss brake hoses, speed bleeders, and brake ducts. I will initially be running on Kumho Ecsta street tires, 275-40-17 all around.
The car is currently equipped with stock saw blade style aluminum wheels.
With that wheel, you can barely see the rotors, which makes me wonder if these wheels present an obstacle to properly cooling the brakes.
Does anyone have experience to say yes or no about this?
The car is currently equipped with stock saw blade style aluminum wheels.
With that wheel, you can barely see the rotors, which makes me wonder if these wheels present an obstacle to properly cooling the brakes.
Does anyone have experience to say yes or no about this?
06-07-2014, 06:12 AM
#2
Burning Brakes
YES , YOUR PROBABLY GOING TO COOK THE BRAKES ,WITH THOSE WHEELS (eventually) .get a decent pad also . hawk blues work well .get the Ducts as close to the center of the rotor as you can .
06-07-2014, 06:25 AM
#3
Safety Car
Danny Kellemyer has probably done the most work on this issue. He's used temperature probes in the pads and actually measured the temperatures while on the track.
He didn't like my CCW wheels a whole lot. They work fine for me but I'm and HPDE guy - not a racer.
So yes - the wheel can make a huge difference. The problem is most of us don't have the engineering capability (nor the tools) to verify our ideas here.
Richard Newton
More Brake Stuff
He didn't like my CCW wheels a whole lot. They work fine for me but I'm and HPDE guy - not a racer.
So yes - the wheel can make a huge difference. The problem is most of us don't have the engineering capability (nor the tools) to verify our ideas here.
Richard Newton
More Brake Stuff
06-07-2014, 08:59 AM
#4
Melting Slicks
The saw blade wheels actually pump air because of the shape of the airfoil element in the wheel. That, combined with a good bit of metal that acts as a heat sink actually makes these wheels work pretty well at extracting air from the wheel well.
There is a low pressure area alongside the car and this extracts air from the wheel well and under the car and this does tend to keep things cool, but the fan shape of the saw blade wheels helps move air out of the area around the brakes and that helps too.
Basically it's a tradeoff. A more open wheel vents a larger area to the low pressure area beside the car, but the saw blade wheel pumps air out of the area behind the wheel. There is a bit less area because the wheel provides some blockage, but that is less of an issue.
With any stock setup a set of spindle ducts is the best thing you can do to reduce brake temps, this goes for C4's, and C5's. The J55 "big" brakes are a big improvement over the smaller base suspension brakes, but without some properly applied cooling you'll cook them too in time and the calipers will spread and they will be shot.
You are doing the right things with the brake ducts, but make sure you have a set of spindle ducts to get the air to the inside of the rotor, the titanium heat shields (to reduce heat transfer to the pistons and fluid) also help. If you could get some air around to the outside face of the disk that would be a big help, because that area isn't well vented with the sawblade wheels, and that is their biggest disadvantage.
There is a low pressure area alongside the car and this extracts air from the wheel well and under the car and this does tend to keep things cool, but the fan shape of the saw blade wheels helps move air out of the area around the brakes and that helps too.
Basically it's a tradeoff. A more open wheel vents a larger area to the low pressure area beside the car, but the saw blade wheel pumps air out of the area behind the wheel. There is a bit less area because the wheel provides some blockage, but that is less of an issue.
With any stock setup a set of spindle ducts is the best thing you can do to reduce brake temps, this goes for C4's, and C5's. The J55 "big" brakes are a big improvement over the smaller base suspension brakes, but without some properly applied cooling you'll cook them too in time and the calipers will spread and they will be shot.
You are doing the right things with the brake ducts, but make sure you have a set of spindle ducts to get the air to the inside of the rotor, the titanium heat shields (to reduce heat transfer to the pistons and fluid) also help. If you could get some air around to the outside face of the disk that would be a big help, because that area isn't well vented with the sawblade wheels, and that is their biggest disadvantage.
Last edited by Solofast; 06-07-2014 at 09:01 AM.
06-07-2014, 09:42 AM
#5
Safety Car
The saw blade wheels actually pump air because of the shape of the airfoil element in the wheel. That, combined with a good bit of metal that acts as a heat sink actually makes these wheels work pretty well at extracting air from the wheel well.
There is a low pressure area alongside the car and this extracts air from the wheel well and under the car and this does tend to keep things cool, but the fan shape of the saw blade wheels helps move air out of the area around the brakes and that helps too.
Basically it's a tradeoff. A more open wheel vents a larger area to the low pressure area beside the car, but the saw blade wheel pumps air out of the area behind the wheel. There is a bit less area because the wheel provides some blockage, but that is less of an issue.
With any stock setup a set of spindle ducts is the best thing you can do to reduce brake temps, this goes for C4's, and C5's. The J55 "big" brakes are a big improvement over the smaller base suspension brakes, but without some properly applied cooling you'll cook them too in time and the calipers will spread and they will be shot.
You are doing the right things with the brake ducts, but make sure you have a set of spindle ducts to get the air to the inside of the rotor, the titanium heat shields (to reduce heat transfer to the pistons and fluid) also help. If you could get some air around to the outside face of the disk that would be a big help, because that area isn't well vented with the sawblade wheels, and that is their biggest disadvantage.
There is a low pressure area alongside the car and this extracts air from the wheel well and under the car and this does tend to keep things cool, but the fan shape of the saw blade wheels helps move air out of the area around the brakes and that helps too.
Basically it's a tradeoff. A more open wheel vents a larger area to the low pressure area beside the car, but the saw blade wheel pumps air out of the area behind the wheel. There is a bit less area because the wheel provides some blockage, but that is less of an issue.
With any stock setup a set of spindle ducts is the best thing you can do to reduce brake temps, this goes for C4's, and C5's. The J55 "big" brakes are a big improvement over the smaller base suspension brakes, but without some properly applied cooling you'll cook them too in time and the calipers will spread and they will be shot.
You are doing the right things with the brake ducts, but make sure you have a set of spindle ducts to get the air to the inside of the rotor, the titanium heat shields (to reduce heat transfer to the pistons and fluid) also help. If you could get some air around to the outside face of the disk that would be a big help, because that area isn't well vented with the sawblade wheels, and that is their biggest disadvantage.
Follow a C4 in the rain and watch how far out they pump air/water...about 3' or so.
Pretty impressive.
06-07-2014, 09:43 AM
#6
I have used the sawblades, sometimes backwards also. Did not have any problems. I'm running spindle ducts that fit the entire inside surface of the rotor for cooling though. HT-10 pads. I had stick on temp stickers on the calipers and they never reached 320F, they went above 220F. I don't think I would run them backwards if no spindle duct. I did run the rear backwards also with no ducts and had no problems. I only used the wheels for 1 set of tires though, NT-01.
I use the titanium spacers and DRM stainless pistons which they have started selling again.
I use the titanium spacers and DRM stainless pistons which they have started selling again.
06-07-2014, 04:06 PM
#7
Tech Contributor
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When I ran my 86 I used the stock 16x9.5 Enkei vented wheels and had air ducted from the front air dam to behind the front rotors. No spindle ducts. On track I would use PFC 83 compound in the front and 80 compound in the rear with the 88 and up big brakes adapted to fit under 16 inch wheels. When I hit the brakes at speed I could see brake dust blow outward from the wheels.
So yes, you can get quite a bit of air flow past the rotors.
Bill
So yes, you can get quite a bit of air flow past the rotors.
Bill
06-08-2014, 06:36 PM
#8
Burning Brakes
Thread Starter
Thanks guys
I really appreciate the expert advice. It seems like the consensus is that so long as I provide spindle ducts, I will be ok. At least for my first year or so.
I will look into the heat shields also.
As I progress in skill, and move up to sticker tires and higher speeds, then I might generate some higher temps, and will revisit wheel selection then.
I will look into the heat shields also.
As I progress in skill, and move up to sticker tires and higher speeds, then I might generate some higher temps, and will revisit wheel selection then.
06-08-2014, 09:15 PM
#9
Melting Slicks
I ran my C4 with the $100 set of Eklers ducts. I don't think they make them any more. They were a small vent in the front air dam, with 2 feet of 2" corrugated pipe.
Serious racers laughed at them, but they worked 100% fine.
Serious racers laughed at them, but they worked 100% fine.
06-09-2014, 03:20 PM
#10
Racer
I'm thinking of buying some HD calipers and brackets and 13" rotors from Rock Auto in order to have the J55 brakes on my 89 ($227). Can I re-use the same brake hoses and when I disconnect them from the old JL9 calipers and attach them to the new calipers, do I need do bleed the system or is it plug and play?