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As also pointed out by others, the heat shock is what seem to cause these rotors to prematurely crack. So-called technical tracks where you use the brakes more are often less shocking to the system, since the temp increases/drops during a lap is much less than those tracks with 70% straight, and some corners in between.
Some of the tips I've heard or started doing over the years:
Do cool down laps at highest speed you can without having to use brakes (we're cooling the car and brakes, not tires). You can do 2 laps, too, if you have time (which I do most of the time).
Once in the paddock, after 5-10 minutes, roll the car a bit (half-wheel-turn) to evenly cool down the rotor. Most rotors do crack/fail at the paddock due to increasing temp differences between the part of it in the caliper vs. the part where it takes more air.
Don't ever bleed your brakes when the system is hot or even when it's mildly hot. Aluminum threads on the caliper will be soft; you're asking for trouble.
If the track has very long straights, consider BLOCKINGthe cooling air ducts to reduce the temp delta within laps.
Some great info in here, thanks guys. Cooling them down at a higher speed sounds like a key point- I’ll make it a habit not to touch the brakes during the cool down lap.
Village, you posted an old map of PBIR. Turn #9 is gone now, it’s just a long back straight. They need to put #9 back in. I reached 147 in my GS and 155 now in my Z at the end of the straight, before crushing the brakes. More importantly, it’s stupidly dangerous. There’s a concrete wall right after a short runoff area. No need for those high speeds without a safe runoff.
2015 z06 running cup 2's. I got 16 days out of the cups as well which doesn't make a lot of sense either.
lol what? I don't think I could get 16 days out of 60k mile all seasons. Cup2 just delaminate on me. They throw chunks. Something is wrong there. Do you ride the brakes or something?
Originally Posted by fatsport
Some great info in here, thanks guys. Cooling them down at a higher speed sounds like a key point- I’ll make it a habit not to touch the brakes during the cool down lap.
Village, you posted an old map of PBIR. Turn #9 is gone now, it’s just a long back straight. They need to put #9 back in. I reached 147 in my GS and 155 now in my Z at the end of the straight, before crushing the brakes. More importantly, it’s stupidly dangerous. There’s a concrete wall right after a short runoff area. No need for those high speeds without a safe runoff.
Really 155 mph, 335 R7s throw off the speedo
Wow, yeah that's dumb. We're spoiled here in Dallas. ECR and MSR are extremely safe tracks with virtually endless runoff save one or two turns. COTA is pretty good but there are definitely walls. Watching some videos of tracks with walls and trees everywhere- not for me.
Yeah that's unusually long life from cup 2s. Perhaps you're not warming up your tires much, either, due to the track layout or some other reason, and relatively cold tires are probably lasting much longer (and also providing less traction than possible)?
Forget the rotors, I'm more shocked you survived a rain day on Cup2
I decided to spend a lot of time concentrating on being smooth. The rain actually helps that a lot. I spent all of last season and so far all of this season concentrating on going smooth not fast. I also concentrated on braking. I kept braking later and harder. Maybe the combo is what helped the ap's and cups last so long.
I'm no pro racer, but I'm a decent driver. Unless there's a much faster car out there, I rarely get passed at HPDE. I have no idea why, but in the rain, I'm blazing fast compared to the rest of the pack. I think it's from driving my super low traction limit miata so much.
It's a good example of how helpful the rev match can become. I failed a shift, and by the time it shifted, the revs were low enough to lock up the rear tires. Normally, you don't blip the throttle in upshifts, and it just didn't come to my mind. This was the 1st lap, and Cup 2s were cold. In any other tire, I bet they would not lock up completely, turning me into a passenger : ) I love NT01s, R888Rs, even R7s for that. They are decent even when cold.
Lap 1 started at paddock. In any case, my experience with Cup 2 has been 3 laps to warm up, 3 laps to perform, the next 3 laps to overheat, to never cool back down enough until leaving the track. I certainly didn't like it. Also, keep in mind that I live in the Pacific Northwest; it's often colder / less sunny here than 'usual' : )
** TL;DR: Most of this is not news to those who've changed the radiator on this car, before. The two specific issues are cutting down the tab on the passenger side radiator mount, and also 'convincing' the top plastic cover to conform with the tabs on the radiator for best seal. **
The new '19 Z06 A8 cars come with a much thicker radiator. Looks like it was deemed unnecessary for '19 Z06 M7 cars, since they come with AUX radiator, but whoever goes to track with these cars know that there's really no such thing called too much cooling : )
What you need:
The new thicker radiator. GM part# 84448529. I sourced it online for $305 + S&H.
Dykes or similar to cut/trim one of the radiator mounts.
1 or 2 gallons of DEXCOOL antifreeze and distilled water. You can get it 50/50 mix as well, but I prefer doing my own. Please note, Corvettes DO NOT come 50/50 from factory.
Steps
Jack the car up, or put it on lift for bottom access. The radiator will not go out from the bottom, but you'll need to drain it and remove one of the lines from the bottom.
Remove the small plastic bottom cover that covers right under the power steering. Once removed, you'll have access to the bottom of the radiator.
This is the left (driver) side of the bottom of the radiator. There is a small valve on the bottom side of the radiator. You just need to loosen it for the liquid to start leaking. At this time, opening/loosening the cap by the reservoir would also help.
Remove the shroud, as well as the air intake box.
Shroud is held in place by 4 x 7mm bolts.
You can remove the line to the radiator at the passenger side top to make it easier to remove the air intake.
Remove the fan.
It's held in place by small plastic slide-on tabs on the radiator, as well as two 10 mm bolts by the sides. Unplug the power cable first for safety, then remove the bolts, and finally detach the cable holders from the fan. Once all done, slide the fan up to remove it.
Remove all the lines/hoses from the radiator.
You'll need a strong/leveraged plier to make it easy enough for you to remove the big lines. The line by the draining valve is held there by a ring. Just remove it (pictured above) to easily remove the line. The other small line at passenger side top corner is removed by pushing its blue colored locking half-ring half way out.
Here is the radiator with all its lines removed. It's amazing how nicely it covers the front nose opening; good job GM! The A/C condenser is installed on the other side of radiator. Due to direction of those plastic tabs, you'll need to slide radiator under for a few inches to untangle them. This was the most time consuming step for me, since I did not want to hurt the hard A/C lines while jerking it around. I recommend braking the plastic locks of the tabs on the top, holding the A/C condenser, especially if you'll just dump the original radiator.
Remove the original radiator, and swap it with the new one.
Here is the new one, temporarily put in place. The original and the new radiators had exact same dimensions except the thickness. You will need to put the A/C back on the tabs at the back of the radiator. For that, a part of the hard line had clearance issues (see pic below).
This is at the passenger side, by the middle. The plastic support of the radiator's main mount has interfered with the sensor port on the A/C hard line.I cut a small piece of plastic from there with dykes, and also unplugged that sensor during install. Once I did it, putting the condenser back on the back face of the radiator got much simpler (and possible).
Once A/C condenser is on, go ahead and put the main A/C mount screws (13 mm) back on. Once you do so, the top shroud tabs will also start to align. You'll then need to put back the lines.The nut-end of the top shroud's side bolts did not come with the new radiator, so I moved them from the older one.
Reinstall the fan, intake, and finally the shroud.
The top shroud bolt holes do not have to align, since we now have nuts on the radiator itself, but I still aligned them anyway by pushing the plastic back-shroud in its place for best air seal possible.
Refill the radiator
My car came from factory with 36% antifreeze. When I drained it, I had about 8 quarts out. I wanted to target 30%, so I used .3x8 = 2.4 quarts of antifreeze, and 5.6 quarts of water to refill. I poured the antifreeze right away, and started pouring the water until it allowed me to do so. You can burp the lines with your hand during this time to let it take more fluid in even before starting the car.
You will need to crank the engine a bit to push the initial air out from the lines. If not, your car will complain about it and throw a few codes. In my case, I just deleted the codes. They will not come back after the first few seconds of engine run. This is also a good time to check for leaks, in case something is not put back right.
Burping, filling to the line, etc.
There are multiple ways to do this. My way is to just idle it a bit while adding more if it empties the reservoir, and rev it to 2-3K RPMs for about 30 seconds. Once done, I just screwed the cap back, checked for leaks one last time, and went out for a drive. I tried to put some heat during my test drive. Once I'm back home, and engine is cool enough (just below boiling is fine), I opened the cap again, and topped it. It has not dropped from that level since then, during my two days of driving.
05-01-2019, 12:42 PM
