Paging bob Bishop regarding c6 brakes

The new C6 uses the same caliper (or so it seems) and uses a 13.4" front disc....

I was wondering if Bob will make something for us to be able to use the C6 brakes up front?

I have the C5 conversion and I am more than pleased with the results... but bigger could be a bit better right?

Sounds great but I doubt a 13.4" rotor would fit under a 17" rim.

I would be happy if the improved 12.8" C6 rotors were backwards comptatable with Bob's C5 setup.

What do you mean improved c6 rotor 12.8? as far as I am converned they are 13.4

anyways I got a set of cross drilled slotted rotors from GM.. $104 each and I hope they do the job well ;)

Only the Z51 cars get the 13.4" rotors. The base models get 12.8" rotors which GM has worked over to improve durability. Supposedly they weigh 2lbs more than C5 rotors.

Right now, no one but GM and their vendor knows if the standard C6 rotor offset is the same as the C5 rotor. We should know by August ’04. Because of the extra weight, I doubt that most C5 front brake system users would be interested, but a few may. The extra 2 lbs/rotor would have the well known disadvantages of being un-sprung and rotating.

There was a “thick cheek” version of the C5 rotor available through Chevrolet for about 1 year. It wasn’t very popular, and GM discontinued them. There was a good deal of debate about them on the ZO6 forum. Many racers tried them, but found that they didn’t last much longer than the regular rotors. Others asked, “Why should we try them when we are not having a problem with the lighter rotor?”. I am not aware of any F-body C5 brake users who tried the thick cheek rotors. They cost (discounted) about $90/each whereas the standard C5/ZO6 rotors were about $50 discounted. They definitely did not last twice as long, but undeniably had more instantaneous heat sinking ability. This C6 rotor could be the same piece. I remember visiting David Farmer’s paddock during the Speed World Challenge GT race at Road Atlanta in 2001. I was hoping to see (and weigh) one of the thick cheek rotors, but he was using the standard C5 rotors, or at least his spares were standards. The weight difference I remember reading in internet posts was 2-3 lbs per rotor.

As it stands, I would not design a bracket for the 13.4” rotor because of the holes in the friction surface. Also, if the C6 caliper body has the same height above the rotor as the C5 caliper, then using either caliper on a 13.4” rotor would require 18” diameter or larger wheels. Alcon and other aftermarket caliper manufacturers have caliper heights shallow enough to install them over 13.5” rotors and still fit in SOME 17” wheels. In theory, a 17” wheel could be engineered to fit over the C5 caliper on a 13.4” rotor, but I do not know of any currently available. Dymag has made some 17” racing wheels with amazing caliper height clearance, but they cost around $850/wheel. I emailed them in 2002 about those wheels and never got a response.

Since C5 and C6 rotors are 1.26” thick, any extra thickness in the cheeks would reduce the internal vent/vane area. Of course, GM has not said that they increased the cheek thickness in order to add the 2 lbs. They might have added more vanes to increase mass. Still, if they increased the metal in the vent areas, then there is less cross sectional area for air flow, and the air flowing through will heat saturate more quickly unless velocity is increased.

(Disclaimer: this is an oversimplification) The only reason that anyone should want the heavier rotor is if you are cracking rotors with serious racing pads. A better, lighter, less expensive long term solution is to get more cooling air into the center of your rotors. Then you may also be able to use a less aggressive (and less expensive) pad, without fading.

Bob Bishop

I shall stay with my cross drilled sloted from GM for now if they work I'll keep using them.. if they dont work I will go back to the reg rotor ;)

Thanks Bob.. and as soon as I know I might order your new brackets... Question... DO YOU FINALLY TAKE PAYPAL?

Thanks

Bob, any thoughts to adapting a more robust caliper to a C5 rotor using a bracket similar to what you're selling? I can get C5 rotors for about $20 a piece now and have no problem with them, but most of the racers have problems with the calipers spreading and that's not as cheap of a fix.

I'm not having a big problem yet but as I start getting higher speeds with more power and try to brake later and later I expect to eventually.

Originally posted by The Highlander

Thanks Bob.. and as soon as I know I might order your new brackets... Question... DO YOU FINALLY TAKE PAYPAL?

Thanks

Highlander, I still don’t take Paypal. As I mentioned in the “ZO6 brake upgrade” thread, “A real world advantage is that they will shortly be available through a sponsor on this board with normal payment options.”

After all the time it will take to compose this, I hope that at least one person reads it.

Mike, there are 2 areas that I consider when contemplating an “upgrade”: the BIG picture and the Details. Details can usually be massaged somewhat (in other words, it CAN be done), but you should ask, “does this modification reasonably fit into the big picture?”

I’ll assume that everything else on the car remains constant, but we’ve added long, rigid, 4 or 6 piston calipers and the requisite pads. A serious racing caliper is superfluous unless it is going to be used close to its capabilities. Assuming you have tires that can sustain this greater rate of deceleration, you can now squeeze the heck out of your rotors. Will the additional heat you put into the C5 rotors be the straw that breaks the rotor’s back? Will the sealed (non-repackable) wheel bearings be able to withstand the increased heat? Lou G. told me many years ago that he couldn’t get more than 2 World Challenge events on a set of front wheel bearing assemblies. What was that, 3 hours total? Even with optional expensive titanium piston inserts and pad shields and SRF, I would probably start boiling the fluid.

OK, so now everything else doesn’t remain constant. We follow race car practice and install 3” ducts in a high pressure area followed by 3” hose and finally a fixture at the rotor to force the cooling air into the center of the rotor. This keeps the rotors within their max temp range and reduces the heat they are putting into the wheel bearings. We then install 2.5” ducts and hose and feed that directly to the caliper to keep the fluid temp in check. That might work. But, if you just did this air cooling work at the start, you might find that the complete C5 system can be optimized to provide 95% of the big caliper advantage. I’m suggesting, as I have in the past, that a driver find the right pad for what he is trying to do. If you have sticky enough tires that you are consistently hauling the car down at 1.2 – 1.4 G’s, it will require a lot of clamping force. Clamping force is what spreads calipers (all of them). But you can reduce the required clamping force by increasing the coefficient of friction of the pads. You will still generate the same amount of heat, and you will need to manage that heat, but you can greatly reduce the amount you are torturing the calipers with hydraulic pressure. I am aware that some racers have spread their calipers so badly that they get noticeable pad taper. I am not making a blanket statement, but less skilled drivers tend to overuse and often abuse their brakes. Have you fatigued a set of C5 calipers yet Mike?

Ideally, the big serious calipers should be paired with big serious rotors. What would be the reason to stay with C5 rotors and use a monster caliper? Besides weight. You have already stated it. C5 rotors are VERY cost effective. Well, so are the C5 calipers. I could go with aluminum hat floating rotors and insure that heat wouldn’t destroy my wheel bearings. But we know what those rotors cost. And read Brembo’s instructions on replacing floating rotor discs on their aluminum hats. It will make you just pop for the whole overpriced pre-assembled rotor system. Brembo’s monoblock racing calipers start at around $4000.00/pr. F-bodies would require larger than the $4000.00 ones. At some point the prices just get stupid for the non-sponsored hobbyist.

So, I don’t think the “big picture” sustains the big caliper idea. Then you get into the “details”. Most of Brembo’s desirable calipers (including the ones they make for Porsche) use a pad that is too deep for the friction facing height of a C5 rotor, and/or they are designed for 34mm thick rotors. AP doesn’t offer dust/water boots. Baer told me that I shouldn’t worry about the $150 rebuild kit price on the Alcon calipers because they didn’t think I would really be satisfied with rebuilt calipers. They said by the time a rebuild kit was necessary, that the aluminum had probably fatigued to the point that I should simply buy new calipers. As far as I know, Baer hasn’t had sales rights to the billet Alcon calipers for a few years. In their $5000.00 C5 front brake kit you get pressure cast calipers, the same material that the C5 caliper uses. That pretty much leaves Wilwood. I don’t like the quality of the “consumer” Wilwood stuff I have seen, and I don’t like their very small pad size. I may take a look at some of Wilwood’s racing product, but it probably lacks DOT boots. I know that racers don’t want or need weather boots on their calipers, but there are very few who would pop for a system designed around a non-streetable caliper and the C5 rotor. I wouldn’t design a bracket for 3 of you. Very few owners would be able to use their current wheels without Band-aids, I mean spacers.

My current conclusion: street and track day drivers do not really need more than the C5 front system, with appropriate pads AND ADEQUATE COOLING AIR. True road course racers in a competition context could benefit from race calipers, but they would only get an incremental improvement, most of which could be obtained with an extra-hearty dose of cooling air and high mu pads in C5 calipers. If the all-out racer wants all-out performance, he needs to buy an all-out brake system, including rotors. But, I can buy a lot of C5 pads, rotors and calipers for the price of one set of the BIG BOYS. The rich kids can often win by pouring money on a problem. I find it satisfying to out-perform them with less expensive but “system optimized” equipment.

Bob

Originally posted by 94bird
Bob, any thoughts to adapting a more robust caliper to a C5 rotor using a bracket similar to what you're selling?


I have heard of guys having fatigue problems with the LS1 f body caliper, but not the C5 unit. So I'll post the same question Bob did... have you yourself fatigued a C5 caliper to the point where it has a noticeable, or measureable problem?

Never have. And I have been using the C5 calipers on street and track since 1998. Still haven't gotten pad taper either; at least none that can been seen with the eye. I am sure I could measure some.

Bob Bishop

Originally posted by lateapex


After all the time it will take to compose this, I hope that at least one person reads it....
Bob

Great analysis. Thanks for the info Bob.

Hey bob :bow:


Question: do you have pics of cooling ducts on an Fbody for the calipers?

I don’t have the ability to host pics, but the pics I have are of other peoples’ installations. Here is one link http://www.go-fast.org/z28/brake_ducts.html with good pics, but I chose a simpler solution. I located the ducts on either side of the front air dam (for the bottom breathing radiator). If you search, you may find install instructions or finished pics of solutions like mine. I have seen them. Actually, I have never re-adapted my steering knuckle fixtures to the C5 rotors since I eliminated my overheating brake problems simply by going to C5 front brakes.

I will be at a trade show in Las Vegas until next Monday night. I'll check in when I get back home.

Bob

Good post Bob, and as you suspect I have never personally spread my first set of C5 calipers that have now lasted one road race and many track days over more than a year. I just took mine apart over Christmas and could not visually see any pad taper. Heck, I have a spare set of rotors and pads that I thought I might use last year, but these are going to last me at least one more race.

IOW, I'm very happy with C5 brakes on my Firebird so far, but all you have to do is go to any Vette forum and you see owner after owner say they're having to replace their calipers because of pad taper. Honestly, I just don't get it. Yes, I'm using some 3" ducting to my calipers, but it's very crudely done. It must be good enough though. I don't have tapered pads, my wheel bearings lasted all last season and still have no play, and I never boil even the cheap ATI Blue fluid. I'm also using some high temp Cobalt Friction VR pads that really stop the car right now.

In my first race to get my comp license with NASA I was consistently outbraking an AI Mustang that was 450 lbs. lighter than me and had Alcon front brakes. He walked up to my car after the race and looked at my brakes and just chuckled. He told me, "I guess I'm not using my brakes to their full potential." Maybe not. :)

I'll continue to use the C5 kit as for me now it's definitely the best option. I'm just always looking ahead to have a backup plan for when I outgrow what I have. If the next step up has a $3000 price tag with $200 rotors I'll just start buying some C5 spare parts. ;)

BTW, here's how my ducts looked about a year ago:

http://mywebpages.comcast.net/miketaylor68/brakeducts.htm

They've been improved in their mounting method near the rotor since then and will be better for this season. I'm specifically getting rid of the zip ties and will duct air more directly at the center of the rotor. I can't for the life of me figure out how to fit a duct to the caliper though, and still leave room for 315 tires at anywhere near full lock. The duct tape you see on the existing 3" hose is where my tires would rub.

This year I also plan to get rid of my lower air deflector and route air through the front fascia to the radiator after installing a front air dam. I'll then use the fake foglight holes for my brake duct intakes. That should help my air flow.

hmmmm... C6 rotors eh?

As listed above, it looks like I'll just stick with plans for a C5 rotor instead. The C5 caliper, and maybe the $80 titanium pad shields are about the limit of cost-effective upgrades I'd imagine. With a C5 caliper you also have the option of stainless steel pistons for more fluid protection if you wanted.

If anyone NEEDs better rotors than the C5's, you may want to look at this option: www.stopforce.com

The Porsche rotor adaptors help limits heat transfer to the bearings, and heat dissipation is supposedly better than the C5 rotor. Recent price drop: $600/pair ($300 each ouch...)

I'd wager air ducting, and a $500 driving school is a much better way to spend the money though. :)

Stop force looks good.. but they are not cheap and I haven't heard bob bishop complaining on the stock ones... hm.. me neither as a matter of fact, but its true that I do not brake in the consistency of a track, but I do break many times when street drving from 150-60 many many times in a row it could be said.

Originally posted by lateapex
Here is one link http://www.go-fast.org/z28/brake_ducts.html with good pics, but I chose a simpler solution. I located the ducts on either side of the front air dam (for the bottom breathing radiator).

By the way, after I had an "incident" that wiped out the nose of my car, I reinstalled the ducts the same way Bob describes, with the intake in the air dam. It's all pretty logical when you dive in, but if anyone needs a pic I'd be happy to furnish it. Since I've sold the car, I have less motivation to keep the web site up to date.... :)

Dave

Send pics to highlander@caribe.net

Thx

Will do, tonight...

Dave

Question--if you can only duct to the caliper or to the center of the disc, but not both, which spot would you choose and why?

rotor, for a few reasons:
1) more efficient use of cooling
a) The air feed to the rotor travels through dozens of internal vanes, and helps wick heat away from the rotor/pad assembly... much more surface area than the caliper fins provide.
b) The delta-T of the air verses the rotors is much higher than that of the air verses the caliper and hense the heat absorbed byt he air passing over the rotor shoudl be greater

2) cooling priorities
Cooling the rotor not only helps keep it from warping, it also helps limit heat build-up in the wheel bearings. I imagine this is the main reason we don't see cast aluminum or tubular steel kuckles... the iron is a good heat sink for cooling the ABS/bearing.