wvumtnbkr Posted October 9, 2018 Report Share Posted October 9, 2018 (edited) So, I am still having issues with killing my brakes due to heat. Here are some facts about similar cars.... Both of these cars are as fast if not faster into the braking zones on the same track on the same day as us. 1) Team Sahleens runs the same brakes same size rotors - they just won a race on a track that we smoked our brakes... 2) A team that swapped an LS1 into their RX7 is using a totally stock braking system with Hawk Blues... No brake problems.... We will destroy a set of Carbotech XP24 in about 20 hours. We have also tried The St43 that everybody says last forever. They last "okay" about the same as the XP 24. However, they feel like crap and provide NO braking force. The brake pedal also feels a bit long. We bleed the brakes every day of every race (need to because the fluid turns black with a quickness). I am thinking about going to a larger diameter master cylinder to improve feel. I am also going to 1/4" wider rotor (still a stock type rotor, just from a different car) with my stock 4 piston calipers. I have brake pressure gauges in the car. I can see that the brakes do not have any residual pressure. We have the mazda motorsports brake ducting kit. I believe our ducting is VERY good. I tried the temperature paint and temperature stickers.... Too much brake dust to tell what color the paint and stickers are. Also, it appears that we are above the top temp range that the indicators show.... So, If I wanted to go to a totally non -stock master cylinder / non - stock prop valve, How would I do it? My current system has 3 ports for the brakes. 2 for the front and 1 for the rear. How do you plumb in an aftermarket system that only has 2 ports? Thanks for any info you can provide! Edited October 9, 2018 by wvumtnbkr Quote Link to comment Share on other sites More sharing options...
Team Infiniti Posted October 9, 2018 Report Share Posted October 9, 2018 (edited) 48 minutes ago, wvumtnbkr said: I am thinking about going to a larger diameter master cylinder to improve feel. And that is ALL you are going to accomplish with a different diameter master, a lateral move if your goal is pad wear. Can you increase rear bias? Edited October 9, 2018 by Team Infiniti Quote Link to comment Share on other sites More sharing options...
Black Magic Posted October 9, 2018 Report Share Posted October 9, 2018 For pad wear, Man it sounds like you have an airflow problem if in fact Sahlens car has same brakes and equal peak speed (straight). If they brake earlier\use more drag to slow the car down this might not count. Any pics of your ducts? With the air dam\aero package you would have different pressure\flow in the area of the brake rotors than a more stock setup. If your hood extractor and fender extractors had some magic and were really efficient the under hood pressure might be low enough there isn't extra flow over the brake parts. For perspective I have 2 drivers that could murder pads. I brake much sooner\back my corners up and thus use less brakes. We are all sub 1 sec different in laptime. Death vs slightly raised pad wear can be a small window in temp. If you want to change the master for feel, and change the bias\proportioning you would simply plumb both fronts together. Does the MC have build in proportioning? If not you could plumb the new MC to the old prop valve if you want to keep it. Otherwise the norm is to plumb the rear brakes to the prop valve, using a real prop valve (preloads a spring) vs the orifice style crap units. The good ones will have piston options and or springs to change both the proportion and blow off point (the knee of the curve, you get to tune an intital bias, crossover psi and final bias). Sure the rear brakes are working well? Remember if they aren't doing their part you just sent all that work to the front axle. Assuming of course your car would allow a more forward bias than you are running now (ie if the rear brakes are at half effort, but would lock anyway, fixing them will only make them lock up sooner and not add to the braking potential of the car). Quote Link to comment Share on other sites More sharing options...
Team Infiniti Posted October 9, 2018 Report Share Posted October 9, 2018 4 minutes ago, Black Magic said: Death vs slightly raised pad wear can be a small window in temp. This Quote Link to comment Share on other sites More sharing options...
wvumtnbkr Posted October 9, 2018 Author Report Share Posted October 9, 2018 We have used some "flow vis" paint to see that the air is flowing into the ducts at the front of the car. WE have positioned the opening of the ducts as close to the middle of the car as possible (about 1 foot off centerline on car). The ducts terminate in a plate that covers the rear of the rotor and most of the air goes towards the center of the rotor. Some of the 3" duct does blow on the back side face of the rotor as well. Sahleens car has duct that looks like it is blowing in the general direction, kinda, of the rotor. Not very effective looking. We get outbraked by everybody. We need to coast the last part of most straights so that we actually have enough brakes to get the car slowed down.... In other words, we are not trying to be the last of the late brakers... Hell, I try to scrub speed through the corner if I can versus using the brakes (Cause they suck). Also, just to point this tidbit out... We are killing Motul 660 fluid as well, so its not just brake pad heat / wear that is an issue. Quote Link to comment Share on other sites More sharing options...
wvumtnbkr Posted October 9, 2018 Author Report Share Posted October 9, 2018 44 minutes ago, Black Magic said: If you want to change the master for feel, and change the bias\proportioning you would simply plumb both fronts together. Does the MC have build in proportioning? If not you could plumb the new MC to the old prop valve if you want to keep it. Otherwise the norm is to plumb the rear brakes to the prop valve, using a real prop valve (preloads a spring) vs the orifice style crap units. The good ones will have piston options and or springs to change both the proportion and blow off point (the knee of the curve, you get to tune an intital bias, crossover psi and final bias). Can you put up a link or something to show pictures or examples of what you are saying above? Wouldn't plumbing both fronts together reduce the amount of fluid flow by half? 44 minutes ago, Black Magic said: Sure the rear brakes are working well? Remember if they aren't doing their part you just sent all that work to the front axle. Assuming of course your car would allow a more forward bias than you are running now (ie if the rear brakes are at half effort, but would lock anyway, fixing them will only make them lock up sooner and not add to the braking potential of the car). We have destroyed rear brakes several times as well..... We get slightly longer wear from rear pads than fronts. Quote Link to comment Share on other sites More sharing options...
Bremsen Posted October 9, 2018 Report Share Posted October 9, 2018 1 hour ago, wvumtnbkr said: The brake pedal also feels a bit long. We bleed the brakes every day of every race (need to because the fluid turns black with a quickness). I am thinking about going to a larger diameter master cylinder to improve feel. Long pedal indicates to me that the MC is a bit too small for the calipers and going larger will raise/stiffen the pedal along with lowering pressure at the calipers for the same pedal input. Quote Link to comment Share on other sites More sharing options...
wvumtnbkr Posted October 9, 2018 Author Report Share Posted October 9, 2018 1 minute ago, Bremsen said: Long pedal indicates to me that the MC is a bit too small for the calipers and going larger will raise/stiffen the pedal along with lowering pressure at the calipers for the same pedal input. This is what I was thinking. Also, I can upgrade to a more available master cylinder and have more peace of mind that this is NOT a master cylinder issue (already replaced it 3 x this year...) Quote Link to comment Share on other sites More sharing options...
Bremsen Posted October 9, 2018 Report Share Posted October 9, 2018 Do you know the increase in caliper piston area over the stock calipers? Quote Link to comment Share on other sites More sharing options...
wvumtnbkr Posted October 9, 2018 Author Report Share Posted October 9, 2018 I am running stock calipers. So were the other vehicles mentioned. Quote Link to comment Share on other sites More sharing options...
Bremsen Posted October 9, 2018 Report Share Posted October 9, 2018 Oh, I thought you changed calipers to something else. So this is all OE hydraulics? What pressures are you seeing at the calipers? Quote Link to comment Share on other sites More sharing options...
wvumtnbkr Posted October 9, 2018 Author Report Share Posted October 9, 2018 Yep, all OE. I have 2 gauges. 1 for the front lines and 1 for the rear. The 1 front line plumbed to the guage is the passenger side front. Pressures are anywhere from 300 psi to 1200 psi (if I really push on it... like turn 17 after the kink at pitt race). When things are working well (near the beginning of a race with new pads and rotors), normal braking pressures seem to be closer to 450psi. Quote Link to comment Share on other sites More sharing options...
Black Magic Posted October 9, 2018 Report Share Posted October 9, 2018 (edited) Rob, Most other mc's in the world are 2 port , front and rear. There are only 2 pistons in nearly every mc, and you probally have 2 front ports going into the front piston chamber. Some cars do it this way to avoid having a seperate y fitting or distribution block. If you are flowing enough fluid to your calipers to need more than one 3/16 port, there is a hole in the caliper. https://www.summitracing.com/parts/dhb-m104458?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-dorman&gclid=EAIaIQobChMIt5z47Pz53QIVBZ-fCh0wkApXEAQYBSABEgIenPD_BwE I assume your duct inlet is in the air dam, on either side of the rad inlet? I can't remember. Does the rotor duct cover the rotor? The idea is to seal the inside of the rotor and blow the air in there. The cheeks, or flat sides of the rotor should be exposed. Given our average velocity, high power brake blower fans may be another great solution (was for me). The big fix is a rotor with wider and larger vane count. Edited October 9, 2018 by Black Magic 1 Quote Link to comment Share on other sites More sharing options...
jmabarone Posted October 9, 2018 Report Share Posted October 9, 2018 What size wheels are the other 2 RX7s running? I know you love 15" wheels, so I'm leaning towards the air not being able to get out thru the vanes efficiently. Quote Link to comment Share on other sites More sharing options...
wvumtnbkr Posted October 9, 2018 Author Report Share Posted October 9, 2018 (edited) The sahleens guys run 15's. The Spedsource guys run 17s. I am about to add 1/4" spacer in my caliper and run a 1/4" thicker rotor. However, the vanes in the rotor are the same thickness as stock. Does thicker rotor with same size vanes help? Not my car, but the same duct plate. You can see how the majority of air goes to the center of the rotor, but a small percentage does go just to the inside face of the rotor. Edited October 9, 2018 by wvumtnbkr Quote Link to comment Share on other sites More sharing options...
Black Magic Posted October 9, 2018 Report Share Posted October 9, 2018 So just adding "cheek" thickness (making the outer flat disks thicker) is usually done to reduce cracking. The heat is transfered from the fins, so you want more fin area (total thickness wider for same cheek thickness). This usually requires a wider caliper bridge, the gap between pads. Quote Link to comment Share on other sites More sharing options...
mender Posted October 9, 2018 Report Share Posted October 9, 2018 2 hours ago, wvumtnbkr said: I have 2 gauges. 1 for the front lines and 1 for the rear. The 1 front line plumbed to the guage is the passenger side front This might be contributing to your long pedal. We took the gauges out of the NCATS car and that helped pedal feel. At the very least, I'd recommend removing the rear gauge, it doesn't really tell you much other than the brake bias and rear fluid movement seems to have a larger affect on pedal travel. Quote Link to comment Share on other sites More sharing options...
wvumtnbkr Posted October 9, 2018 Author Report Share Posted October 9, 2018 1 hour ago, Black Magic said: So just adding "cheek" thickness (making the outer flat disks thicker) is usually done to reduce cracking. The heat is transfered from the fins, so you want more fin area (total thickness wider for same cheek thickness). This usually requires a wider caliper bridge, the gap between pads. I am adding 1/4 inch caliper thickness. I'm now looking at 2 piece rotors that are 1inch thick by 12" diameter. I am currently running .8" thick by 10.75" rotor. Quote Link to comment Share on other sites More sharing options...
mhr650 Posted October 9, 2018 Report Share Posted October 9, 2018 I don’t see how Mazda used anything different than the rest of the automotive world for brake components, but on the stock car the brake components are on the cold side without any exhaust heat to deal with. Now you have exhaust on the same side as the brake components. One of the beauties of the dual master cylinder system I am going to is that all of the components are inside the car. As for plumbing you would run the line from the rear master cylinder down the transmission tunnel to a proportioning valve mounted somewhere close to the balance bar knob so the drivers can reach them for adjustment, then back close to the diff and through the floor with a bulkhead fitting. The front master cylinder would go through the firewall with a bulkhead tee fitting and then on to the right and left front calipers. The clutch hose could go through the firewall or transmission tunnel with a bulkhead fitting depending on which fit better. Quote Link to comment Share on other sites More sharing options...
wvumtnbkr Posted October 25, 2018 Author Report Share Posted October 25, 2018 So, here is my current dilemma. I am trying to piece something together for decent brakes on the RX7 (yes, while retaining 15 inch wheels).... There is exactly 1 BBK for FC RX7s. It is the mandeville BBK. Must run 17 inch wheels.... The stock rotor is a 10.75" diameter by .810" thick. Would upgrading to a 10.75" rotor by 1.00" thick make a difference? Is it worth the hassle? I coul deven go to a 1.1" thick rotor if that is worthwhile. This allows me to keep my calipers and spindle and hubs, etc... None of that stuff changes. IF the thicker rotor would be an improvement, does it matter how the rotor acheives this new thickness? Meaning: I have the choice of 2 rotors. 1 has a wider middle vented area. The other has a stock width vented area but a thicker "cheek" thickness. Is one of these considerably better than the other? The rotors with the stock size vented area are pretty darn easy to get and put on the car. The rotors that have the wider vented area are probably gonna cost me points due to the 2x rule. Quote Link to comment Share on other sites More sharing options...
ablesnead Posted October 26, 2018 Report Share Posted October 26, 2018 In general with air cooling the more air , the better ..wider gaps between discs help with that....but you have limited the air to your vanes with your cooling plate design....blowing on the rotor surface should be a lot less efficient use of the available air than passing it all through you vanes....we use a deformed tubing end at the plate so that as much air as possible does flow through the vanes....caution...deforming a circle losses cross section...try to fabricate the best compromise....also use titainium brake pad backing plates to give the air about 8 times longer to cool , before the heat travels to your fluid Quote Link to comment Share on other sites More sharing options...
ablesnead Posted October 26, 2018 Report Share Posted October 26, 2018 Looks like you are doing the Mandeville mod now ..that works on 15" wheels....Saki bomb makes a wilwood kit , I think it requires larger wheels Quote Link to comment Share on other sites More sharing options...
wvumtnbkr Posted October 26, 2018 Author Report Share Posted October 26, 2018 I'm not sure the Mandeville mod works with 15" wheels. If it did, that is the easy button. I'm trying to do a modified Mandeville with smaller diameter rotors. I know somebody with the Mandeville brakes that is localish. I'm gonna try to take a few of my wheels and see if they fit. Quote Link to comment Share on other sites More sharing options...
mender Posted October 26, 2018 Report Share Posted October 26, 2018 20 hours ago, wvumtnbkr said: IF the thicker rotor would be an improvement, does it matter how the rotor achieves this new thickness? Meaning: I have the choice of 2 rotors. 1 has a wider middle vented area. The other has a stock width vented area but a thicker "cheek" thickness. Is one of these considerably better than the other? The rotors with the stock size vented area are pretty darn easy to get and put on the car. The rotors that have the wider vented area are probably gonna cost me points due to the 2x rule. I would go for the wider vent area for more flow through the centre of the rotor. Should be a little lighter as well. The C5 calipers work with 1.1" wide rotors and should be within 2X. Quote Link to comment Share on other sites More sharing options...
wvumtnbkr Posted October 26, 2018 Author Report Share Posted October 26, 2018 31 minutes ago, mender said: I would go for the wider vent area for more flow through the centre of the rotor. Should be a little lighter as well. The C5 calipers work with 1.1" wide rotors and should be within 2X. I am using the stock calipers that can accept up to 1.1" with caliper spacers. I already have the caliper spacers. Thanks for the tip. If I change calipers, I will look into those. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.