J8635621

iTrader: (10)

I'm willing to bet he doesn't grandma the car around. I understand your point, but when you spend the time and money to build a car like he has, you are not the kind of driver that just wants to look cool. He passed that point about a million hours and thousands of dollars ago.

YeahYeahYouWere

iTrader: (1)

Right - I'm certainly not suggesting he's hanging out in the right lane watching the Buicks blow by. But the stock brakes on this car are really quite good and can handle some pretty aggressive driving without missing a beat.

TC even mentions he doesn't do cosmetic upgrades - I'm just trying to gauge the true value or a brake upgrade as I genuinely believe a lot of people who put upgraded brakes on this car don't get any true return on their investment.

LionZoo

Please, leave the condescending tone out of this. If you want to discuss we can discuss, but if you're going to act like a camp counselor then I'd rather just not have this discussion.

We've tried wave-style rotors on both the FSAE car and the Baja car. The primary attraction was the lighter unsprung weight, but that's mainly a team psychology thing. While wave rotors are great in concept; in addition to the weight reduction they supposedly boast greater stopping power due to the "sawing" (it's late, my vocabulary isn't as good as normal) action of the rotor's edge on the pads and their profile's ability to better break the boundary layer of gasses, they are harder on pads and they simply don't have the thermal mass of traditional rotors. It's a matter of trade-offs in the end. The FSAE guys stuck with traditional rotors while the Baja team used a similar scalloped design. If I remember correctly this decision is actually quite reflective of which side of motorsports prefers the wave rotors versus the traditional circular rotors.

c41250n

iTrader: (5)

brakes are something very important, i wouldn't use DIY brakes!!

PhillipM

It is indeed, but the loss of surface area wasn't a problem in itself, was it?
Which is what I was getting across.

The reduced surface area for less chemical friction is compensated for (in a correctly designed wave rotor anyway), by the longer torque arm by concentrating more mass to the outside of the rotor.

ChrisRX8PR

iTrader: (1)

Even though I don't autocross fade does all of a sudden become an issue. I can get to 100mph with one step of the gas in 3rd gear almost instantly (yes loosing traction up to about 70-80). When the boost kicks in it just happens instantly and I cannot help it. This provides for the ability to reach triple digit speeds in distances where the car would normally only reach 70mph...which means I have less distance to stop than normal relative to the speed I am traveling at. So I can't just coast and slowly brake to normal speeds....I will sometimes have to slam on them and stay on them until my speed gets to 50...and from 140-150...you get fade with one single stop...no need for 2 or 3 stops...just one straight stop from 150mph and you will get fade when you reach about 50mph on your way to zero with the stock system(ask me how I know )....your pedal will get mushy and you will have to let go and let them cool for a few seconds before getting back on them which is not a good thing...

I don't do it often...so my discs will not be cracking unless there is an emergency and I have to slam on them(at which point I will replace them if I have to)...I just want the safety for that one time I will need it.

Also, the calipers I am using are nothing out of the ordinary. If you look at what TCE uses for their brake upgrades, the calipers don't cover the full face of the disc, they are meant for two piece discs which have really big hats. the contact surface between the caliper and the pad is still bigger than stock, its just concentrated on the outer area of the disc where it can provide a little more leverage. Either way, I plan on switching to two piece discs, maybe larger, in the near future...this is just to prove the caliper brackets and the calipers themselves more than anything.

Best regards,

Chris

YeahYeahYouWere

iTrader: (1)

Chris - that makes an awful lot more sense now. Obviously, more power means you are capable of more speed and thus may need more braking power. I hope I didn't sound dismissive of your idea, as that was not my intent, I was just curious exactly why it was needed, and your driving habits were the missing condition

ChrisRX8PR

iTrader: (1)

I completely agree with the fact that braking from 80mph is the same regardless of HP. But like I said before, I am not talking about 80 here...normally if you want to go 140-150 in your car you would find a long stretch of road where you know you have plenty of space to brake and then you go for it. I am talking about putting the hammer down at hwy speeds and within 1/4mile be doing well into triple digits...and then having to stop without lifting once.

Its kinda hard to understand but it does get you when you actually drive the car. The stock RX-8 brakes from 60-70 and 100 in the same distance as a Ferrari 360 Modena. The difference is that from 150 the Modena will brake without fade and the rx-8 will suffer fade greatly at about 50mph when braking from 150mph because that is a "top speed" stop for the rx-8 but not for the ferrari and the ferrari brakes are not larger diameter...they just have cross holes...and nice calipers with more rigidity and better heat dissipation. My new calipers and caliper brackets are all aluminum...which will dissipate heat way better than the stock cast iron units.

Chris

ChrisRX8PR

iTrader: (1)

No problems, I like when group discussions, they are a great way to notice potential problems with designs.

I don't normally drive over 100mph...but this is for that one time I do and some old lady runs into my lane and blocks me 1/8th mile ahead and I have to slow down with one stump of the pedal.

I appreciate everyone's concern and I welcome more discussion of the subject.

Chris

YeahYeahYouWere

iTrader: (1)

I'd say bringing it to a halt from 150 falls outside what I'd call "average braking" lol. The stock brakes on the RX8 are truly exceptional, but they are simply not designed with 150 mph stops in mind.

I'm outside my element when talking about max speed stops in the 8, because the fastest I have driven mine is 116 - and you're exactly right I did in the middle of nowhere on a perfectly straight road (freshly paved even).

Seeing as you actually use that HP, I fully understand why you'd want to upgrade the brakes.

Highway8

iTrader: (11)

So i took a look at the brake pads that the wilwood sl6 uses and they are 4.74" X 2.43" verses our sock size of 5.44" X 2.44" but the shape is different so I dont know which ones have a larger contact area. Either way, my only concern with any caliper upgrade is the brake bias. I spoke to a engineer that designed a 14" front brake kit for the rx8 using willwood calipers. He said that until he installed an adjustable proportioning valve the stopping distance was increased not decreased because the rear brakes where not doing enough work. I dont know all the tech specs, but my understanding is that with the smaller pistons on a 4 or 6 piston caliper, it requires much lower brake fluid pressure to operate the brakes so your front brakes will do all the work.

I track my car 4-5 times per year and have had very good success with racing brakes 2 piece open slot rotors using hawk ceramic pads and hawk HP Plus pads. The track I go to has 3 straights that I reach 120 MPH and 2 of them are followed by turns under 50 MPH. I stand on the brakes hard enough to activate the ABS with 245 r-comps. Even with all the hard braking I do, I have never had any brake fade. Another thing I have found is that on the street (ceramic pads), my rear brake pads have less wear then the front but on the track (hp plus pads) my rear brakes wear faster then the front.

I am upgrading to 275/35/18 tires and might be running hoosiers so I should no longer be able to lock up the brakes. I will see how things go and I might go with racing brakes 4-piston stock rotor size calipers. Their pads are 4.69" X 2.45". Racing brake says that an adjustable proportioning valve is not required but I will be installing one anyways.

ChrisRX8PR

iTrader: (1)

I agree...that is why I kept similar total piston area and stock rotor diameter(which I will eventually to a stock diameter, thicker 2 piece rotor). I didn't want the bias to change so much. I am not worried about increasing the braking distance slightly if that is what it ends up doing...

I am worried about being able to brake without fade...even if it takes 10-15ft more...who cares....if the stock ones can do it in 10ft less but they fall on their face and you loose all braking force due to fade when braking from 150mph...then the theoretical shorter distance does nothing for me because it will be doubled by fade.

Chris

ChrisRX8PR

iTrader: (1)

I noticed something is off on the pad dimensions you posted or we are talking about different ones. The pads for the calipers I got are less tall (this is why they do not cover the entire face of the rotor),so if stock is 2.44 the ones I got are less and they are longer than stock so they cover more area at the outside of the rotor...maybe my calipers are slightly different to the SL-6's.

I will search and get back to you.

Chris

olddragger

iTrader: (3)

chris--isnt fade more to do with the right pads and fluid? We Ga rx8 club guys have thousands of miles on the track and I have approx 1K AFTER i placed the S.C etc on the engine. I get to speeds of 135+ pretty easily and when I am running the carbo tec xp8's with a 275 shaved nito 1's I have never had any brake fade.
As long as I dont overheat the rotor--its all good.
I still like your set up
olddragger

ChrisRX8PR

iTrader: (1)

Maybe that plays a big part. I am no expert when it comes to pad combinations...you guys know what I do best and it isn't slowing down...on that note, the pads that will go in with the 6 piston calipers are Hawk HPS pads which should offer a significant improvement over the OEM ones right?

I will upgrade the brake fluid while I am at it to a high temp one....overall..my fade should be reduced and my caliper flex should be gone...that is what I wanted with the setup.

Chris

Todd TCE

Having been around this topic and some of these parts for a bit....

The debate over scalloped rotors has been around for some time now. It's all a trade off; weight for overall efficiency. There is simply no way to get the same thermal capacity from a rotor with 20% of it's mass removed. Great for drag racing, autoX use or such but not a wise choice for anyone considering open track day use.

The pad size vs swept area etc topic Phil covers pretty well. Competition caliper tend to favor a higher Effective Radius (Er) for the increase in torque while balancing rotor and hat weights to not make a boat anchor size package. I'd take a larger rotor over other options nearly any day; Greater Er, greater mass, greater swept area (at times) vs over working a smaller rotor with very aggressive pads. The taller pads (viewed horizontally, confusing) will often be found on a street car for longer wear and simply being more stable for longer use.

With regard to the six pot caliper on 14" rotors I'd have to agree. For the record: it never came from me. Despite the hard-on for bragging rights of a greater piston qty adding all of this doesn't necessarily guarantee great returns. Some improvements in pad wear over a conventional four pot is about all that's going to be had- area being the same. However as a general rule the increase in rotor size should net a decrease in piston area. To make the 14/6 combo work correctly (without bias ****- another totally mess proposition) the only way to do this would be to equally add the necessary rear changes; rotor size, pads or piston area. All this proposed added area creates another problem though; loss of pedal feel!

I'll be happy to post the bias percentages calculated later.

Highway8

iTrader: (11)

Todd I recently become familure with the kits you produce for the RX8. I wondered if you could answer a few question.

First, if the front caliper is changed to a 4 or 6 piston aluminum caliper either but the rotor is stock sized, like the racing beat caliper or the setup chris is going to use, how much will it effect the brake bias and will the overall brake effeciancy be improved. What should be done to the rear? Adjustable proportioning valve, pad/rotor change?

With the kits you offer, does the brake bias stay near stock when the rear kit is installed. Similar bias with all 3 front brake options? Do you know the weights of the rotors on all 3 rotors 14 X 1.10, 13.3 x 1.265" and 14 x 1.265"

How about the caliper weights? Does the rear kit use a completly new aluminum caliper bracket for a little weight reduction?

I really like the plus 2 brake option you have. the 13.3 x 1.265" rotor should be a great balance between size (bigger and thicker) and weight.

olddragger

iTrader: (3)

yep thats in the right direction---hawks are a decent upgrade and getting the high temp fluid (ate blue maybe) will surely help

I agree---you arent known for how well you slow down---made me laugh dude and its good for an old man to do that--except i almost peed in my pants.
olddragger

Todd TCE

I'll try to answer as discretely as I can here.

LionZoo

Get buried in work for a few days and come back and WOW. Anyway still have work so this will be quick.

Todd basically said what I had to say about thermal capacity of the scalloped rotors. I think I hinted at that anyway by comparing the choices made by FSAE (a Formula car) versus BSAE (a Baja off road car with 1/10th the horsepower).

For this application, yes the longer lever arm necessitates less actual thermal heat dissipation, but that is being offset by a smaller pad area so that energy is being concentrated into a smaller area. Also I worry about the temperature gradient that the rotor will experience since only a portion of it used, which might lead to thermal expansion issues. I do love Chris' idea of painting over unused area though.

In terms of calipers, a good fixed caliper is going to be a significant improvement of a sliding caliper, there's just no way around it.

I have the Hawk HPS pads on my car right now and I have to say they get a thumbs down from me. In my opinion they're even to a slight downgrade from stock pads. They're slightly more temperature stable, but they also feel like they just don't have as much overall bite. I have a set of Cobalt Friction GT-Sports about to go on, so we'll see how that goes.

olddragger

iTrader: (3)

cobalts are good pads--getting harder to find for us in Georgia. One thing about them--if you get the pad material on your wheel--dont let it set there--it can be a bitch to get off.
I really like the carbo techs--they have been an excellent track pad. Can also travel with them on.
olddragger

PhillipM

^^Have to agree with that, Carbotech XP10's are an awesome track pad.
Streetable too if you don't mind a little noise.

shadycrew31

iTrader: (6)

My bad ya'll.

Spin9k

...hard to find in GA....hells bells ... I get my Cobalts in Marietta ...and I'm in NH FCOL Here the place you need to call http://rpgproduction.rpmware.com/default.aspx search for 'cobalt'... great people ... great prices ... excellent service ... and they're very informative to talk to.

c41250n

iTrader: (5)

how much did it cost you just parts alone?