Brakes on 997 Turbo

[okellyt]

for my C2S I initially upgraded the quality of brake fluid to one with a higher operating heat range (cant remember detail) and put Yellow stuff which I found very good and highly feel some.

When discovered the master cylinder was the same a off the Turbo'on Powerkit C2S' and both disks and pads had worn I put the full GT braking system (all the way down to cables) on the beast, with yellow stuff pads. hen the thing stopped on a tuppence

 

[duncangould]

thanks chaps. I have checked my invoice and Porsche did replace the brake fluid - this is a year ago now. I am assuming it is hydroscopic [hydrophobic - or whatever the correct term for not attracting water is] so it should still be ok I guess. I think i will change the fluid to Castrol SRF and see what happends as it did seem to be a fluid problem - post session sponginess and pedal travel. then i think i will change the pads to Pagids. If i were to upgrade the discs to gen II will i need new calipers too? Would the gen II discs be a good idea or should i go further? Are the Turbo S discs different again; I guess so as the calipers are different? Anyway I think discs and calipers will be pretty pricey....

 

[RJKflyer]

ORIGINAL: tscaptain

Indeed they are Ralph. I have a set here and when we (as in PC and me) compared them to the OE it was hard to see how the GT3 ducts would produce significantly more cooling. The OE ducts spread the air over a larger area of the disc whereas the GT3 ones seem to be more "focussed" , if that is the right word, but are narrower. But maybe in practice they do as I seem to recall they use phrases like "more aggressive![]

Yes, I have a pair of GT3 ones in the garage, but on inspection they appeared a good deal LESS useful than the original Gen 2 turbo ones, so in the garage they've stayed...

The GT2 ones are expensive, and I believe require rework to the wheel arch liners to afford them the bigger air feed that they seek to manage.

 

[RJKflyer]

Meant to add that I found Titanium shims useful on the RS4 when I used harder pads - aside keeping heat out of the fluid, they kept heat in the pads, which in this case was good as they worked better hotter.

 

[Lancerlot]

ORIGINAL: duncangould

thanks chaps. I have checked my invoice and Porsche did replace the brake fluid - this is a year ago now. I am assuming it is hydroscopic [hydrophobic - or whatever the correct term for not attracting water is] so it should still be ok I guess. I think i will change the fluid to Castrol SRF and see what happends as it did seem to be a fluid problem - post session sponginess and pedal travel. then i think i will change the pads to Pagids. If i were to upgrade the discs to gen II will i need new calipers too? Would the gen II discs be a good idea or should i go further? Are the Turbo S discs different again; I guess so as the calipers are different? Anyway I think discs and calipers will be pretty pricey....

You would need to replace callipers and rotors, but I'm not sure the improvement would warrant the expenditure. For the same or less money, I think there are better solutions. Tom (okellyt) has experience upgrading the Gen 1 brakes and I'm sure he'll be along with his suggestions later.

As regards the Turbo 'S' brakes, these are carbon ceramic and with the kit costing around £15K + VAT and fitting, as I indicated earlier, it would make more economic sense to ditch your current car and purchase a Turbo 'S'.

BTW racing fluid is highly hygroscopic and will need more regular replacement than the standard stuff, which I use and change every 12 months without any problems.

Regards,

Clive

 

[bobfair]

I had a Gen 1 Turbo that I tracked regularly. Here is the car going through Eau Rouge at Spa





I found the car very quick down the straights ( The car was chipped by DMS) but when you got to the breaking area you would really notice the weight of the car and the brakes working very hard to deal with slowing all that mass. The standard steel brakes on the Gen 1 were 350mm in diameter at the front whilst the PCCBs were 380mm. I had the PCCBs but still felt the car could do with more breaking power when it was used hard on a circuit





Interestingly the PCCBs are now up to 410mm on current models which obviously offer a lot more stopping power than the 350mm as you have a much larger surface area.

I enjoyed my track days in my Gen 1 Turbo as it was so quick down the straights and considered upgrading the brakes but decided against it switching instead to a GT 3 that was more fun in the corners but slower down the straights.

When I switched to my Gen 2 GT 3 the biggest difference on track was in the breaking area. It was so much easier to slow the car and it turned in so much easier than the Turbo which wanted to go straight on.

I am sure you could upgrade the Gen 1 Turbo brakes to last longer on track and/or to provide more stopping power but that weight is still going to make it feel heavier than a GT 3 in the corner. I guess the choices other than improving the cooling and the fluid are: 1. Change the pads 2. Change the discs and pads or 3. Change the car

It would be interesting to hear from John who has used a GT 3 and a GT 2 on track as well as a full race car

 

[duncangould]

thanks for the advice. I think for now then its going to have to be a change of pads and fluid and live with the fact that the Turbo is heavy and get the 964 RS out of moth balls. There was a lovely 991 GT3 at Goodwood - maybe the prices might drop a bit when the RS comes out next year???

 

[Lancerlot]

Bob,

Have you just overtaken that lot in the photo ....or are you about to be lapped!

Regards,

Clive.

 

[lowndes]

ORIGINAL: duncangould

thanks for the advice. I think for now then its going to have to be a change of pads and fluid and live with the fact that the Turbo is heavy and get the 964 RS out of moth balls.

Just to refresh your memory of how suited the 964RS is to the track and how good the brakes are.........but depending on how long its been in mothballs, it might have gone up a bit in value, certainly viz a viz a Gen I turbo. []

 

[bobfair]

Have you just overtaken that lot in the photo ....or are you about to be lapped

On the track days I have done there is always someone faster and sometimes someone slower than me so makes it fun. On that particular day at Spa I had the privilege of being driven round in my car by Mile Wilds. I just could not believe how much quicker and smoother he was. Cars that I struggled to keep up with were passed easily yet the car always felt better balanced allowing him to carry much more speed through the corners. The wear and tear on the car was much less than when I was driving and the lack of breaking power seemed far less of an issue for him than me

The only thing that is more enjoyable than Spa in a 997 Turbo is this:

 

[duncangould]

yes that's why the 964 RS is in mothballs at present and not on the track. I was having a conversation with some PCGB members at Le Mans and they told me how much my car was now worth!!! Although at a recent Goodwood trackday there was a blue 964RS like the one above and a lovely speed yellow 993RS - I just need more guts I s'pose. I must say that the turbo was fantastic around the circuit, the only issue was at the end of Levant when I was clocking 144 mph; you could just feel the brakes trying to work very very hard, elsewhere it was ok it just felt very difficult to get anything wrong.

 

[RJKflyer]

At the risk of being very provocative, the principal reason that PCCB discs are bigger is due to the fact that the ability of the ceramics to reject heat is far lower than steel, hence the larger diameter required to keep even on that score.

Yes, the increased potential pad area, provided it's fed with a higher pressure system, should also produce more brake torque.

 

[Lancerlot]

The PCCB rotors are the same size on 997, which have 19" wheels.

They are bigger on 991 because they can be, due to having 20" wheels. A larger swept area provides improved retardation and better heat dissipation.

The advantages of PCCB's are a reduction in brake dust, unsprung weight and rotational inertia.

Regards,

Clive

 

[RJKflyer]

I thought the 997.2 PCCB were 380mm versus steel 350mm?

 

[okellyt]

ORIGINAL: RJKflyer

I thought the 997.2 PCCB were 380mm versus steel 350mm?

indeed they are and far superior too........[:-]

 

[lowndes]

ORIGINAL: okellyt

ORIGINAL: RJKflyer

I thought the 997.2 PCCB were 380mm versus steel 350mm?

indeed they are and far superior too........[:-]

On 991's with 410mm front brakes the calibration is not good at low speed where it is difficult to modulate braking unless using the very lightest of touches. For road use 997.2 PCCB are better than equivalent on 991. (Ditto handbrake but that's another matter [])

 

[RJKflyer]

ORIGINAL: A larger swept area provides improved retardation and better heat dissipation.

Regards,

Clive

An interesting subject.

The larger swept area only improves retardation if the master cylinder is changed to give a higher pressure at the caliper.

Even then, the impact of swept area is smaller than one might think - it is 'effective radius' that matters which is inside plus outside diameter divided by 4.

Personally, I think PCCB are larger than steel because they have to be, although clearly agree that they can be.

BTW, I'm not disputing that PCCB is better - I've caned my steel discs and they're vibrating so they are clearly on their way out - which I'm assuming I couldn't have done with PCCB.