NJ-GT

Dan,

I'm looking for those rear stock steel 350mm rotors as well. There are hopes that the rear 997 GT3Cup ones will fit or the 997 GT3 street car. ViperBob is helping us on that. So Problem 1 is almost solved (in progress).

Problem 2: What to do to prevent front rotors failing that often? Front Steel Rotors are cheaper than PCCB, but at $500 ea and failing pretty often in pairs, it ain't cheap. Stock steel rotors run for $1000 ea.

What to do?
- Cut two openings on the front spoiler lip
- Use the Cup brake ducts (deeper than the stock ones)
- JongBloed wheels
- Decrease the front wheels offset
- GT3RSR front bumper
- Use slotted rotors, brake pads are cheap.
- 15" rotors and new front calipers
- ...put your suggestion here...

DanH

NJ-GT - in the UK the alcons & brembo's seem to be more well liked for the front mounting. People who were getting 4-5 days out of a set of OEM rotors have got 10days plus out of a set and they are still holding up fine. Only issue is the noise - even the cost isn't too bad. The noise is apparently ok on the newer alcons with lesser float, but I need to give it some time to hear reports from others. The guys who fit them are a race shop, so they don't really understand why I'd care about noise!

Got my fingers crossed that the 997 rotors fit ok on the rear.

viperbob

1) Get Cupcar Ducts
2) Get Motorsports rotors. These sell for on a little of $300 each.....

The 997 Cup rotor is on its way

DanH

I enquired about cooling with the shop I use and got the following response (hope they don't mind a cross post from their Q&A section) :

----
Brake cooling is not an issue any more the only cars that had problems were the MK1 GT3 because they had smaller 330mm brakes 4 pot callipers and no air flow through the wheel
For the Mk2 Porsche changed the way the air exited the radiators they also added air scoops to direct this air through the wheel + 350mm discs and 6 pot callipers
Standard steel discs will crack after 2/3 track days ceramics will start to disintegrate after 12 days this cannot be cured by extra cooling ducts only delayed a little
-----

He went on to say that the newest alcons are 360mm front. They should last 20 trackdays + and not rattle. Apparently the hats can't wear since they have stainless steel inserts where the bobbins are attached. The rears are just rotors and reuse the hats from the ceramics.

I'm inclined to trust these guys as they maintained the car that won the GB Porsche Cup this year and clearly know their stuff.

NJ-GT

Steve @ JZMac...? I trust them as well, but brake cooling is still an issue on the 996 GT3 mk2. I have checked that with my pyrometer on track days.

Do this, next track event, look for someone with a similar driving style and similar lap times driving any other car. Check your front and rear rotors temperature and the ones on the other car, as soon as the track session is over. I always get a large gap on rotor temperature between front and rears.

The 996 TT doesn't crack rotors as often, the X50 TT is much heavier and uses smaller rotors (Turbo S being the exception due to PCCB). The TT has a grill on the fender liner that the GT3 doesn't have, and it has the openings on the spoiler lip (now included on the 997GT3), and it rides 20mm higher so there is additional air flow. There must be a reason why the heavier car, smaller rotors, doesn't crack the rotors as often.

Flying Finn

I'd do something like that.

Cut the opening on the front spoiler and run 2,5" or 3" duct all the way to the brake. Not just near the brake but so that the duct is almost touching.

I had over heating problems in my 993 and when I ran ducts from the front to the brakes, over heating was not problem anymore.

After a cool down lap when I measure the brake temps with pyrometer front and rear disc temperatures are about the same and I'm sure during the hard driving fronts get much hotter so those ducts really help which is the cooling during the cool down lap shows.

DanH

I'll try that. I've scanned the temps with my pyro before, but to be honest had no frame of reference. I do get a gap in rotor temp front to rear, but don't find that very surprising given the obvious requirement for frontal bias.

Yes it is Steve@JZM, and I guess he covered himself in that response as he only says it slightly delays the problem

360mm Alcons on front should help a bit too as they ought to have a higher heat capacity and presumably be more efficient at exchanging heat with passing air. Can't help the unsprung mass though.

DanH

Cargraphic seem to have 2 kits that both involve cutting up bits of the car. I'm not sure where the 2nd kit gets it's airsupply from.

http://www.cargraphic.com/index.php?...,1585/&start=3
http://www.cargraphic.org/index.php?...esolution=1024

NJ-GT

A temperature gap between front and rear is ok. My 150-200 degrees (Farenheit) difference is not ok. I have to rebuilt my calipers before the season starts as a consequence, and my yellow calipers were just installed last year.

The unsprung weight discussion on PCCB vs. Steel rotors is an interesting one. My front stock steel rotor weighs 26#, the PCCB 12.5#. The stock GT3 front wheel weighs almost 25#, and the BBS 1-piece Mag 16#. The RS uprights are much lighter (I will report the weight difference later on). The stock springs are heavy compared to what I have right now from Eibach. A front 275/35R18 RA1 weighs 30# while the 265 GoodYear slick weighs 20#.

DanH

In terms of weight I'm assured that the hatted aftermarket rotors are a lot less heavy than the OEM steels, so it should fall somewhere between the two extremes I guess.

I dunno if I can be bothered with race wheels. I'm a bit paranoid they'll get ruined unless I spend my life polishing them With 5000 USD of brake work on the cards, not sure I can spare the cash anyway.

Got a trackday in a couple of weeks so I'll see if I can pay some more attention to the pyro results on my RS.

mitch236

I don't think you can count springs as unsprung weight.

Nordschleife

Mitch

Think of the car as static, the springs are part of what goes up and down....

R+C

mitch236

Not really. The bottom of the spring does indeed go up and down but the top is fixed. Otherwise it wouldn't do anything. I don't know the answer for sure, but it seems to me that at best, you can only count part of the weight savings towards unsprung.

DanH

Spring and damper must constitute something as it is part of the reasoning to have inboard dampers actuated by pivoty things (yeah thats a technical term )

viperbob

aka bellcranks.

Standard spring / shock assemblies are unsprung weight (Ok we are not talking inverted shocks here but standard ones for these cars). This is why the more expensive shocks have aluminum bodies, and just hold on as the titanium spring revolution is almost here.....