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Been planning for a big brake kit for a while now, so I bought an almost new brake setup (calipers, rotors, & pads) for an amazing deal, way too good to pass up even if it's for a 992 GT3RS and I don't have a 992 or a GT3!
So why not see if I can make them work on my 997.1 CS as part of the ongoing fun projects for the car. I've done all the measurements for spacing and fitment and so far it looks like I'll be able to make it work with mostly stock/readily available parts. Majority of parts are OE 992, some 997, and a few generic ones to fill the gaps.
Goal is to improve on braking during mountain driving and keep as close as possible to upsprung weight of stock 997.1 setup (replaced parts).
I started test fitting and quickly found that my 19" wheels won't work. I've had my eye on some new wheels, so decided to try 20s even though all I've read is that they won't look good on a 997. Bit the bullet and got some, installed, and I think I see the reason why: the stock calipers and rotors look out of place. What luck! I have a set of ginormous calipers and rotors to make it amazing. Then found that the stock 992 GT3 front rotors won't work; no problem, called Girodisc and they recommended ones that will work on the 997 and they're the 410/390mm rotor setup.
I have weights for everything and from initial calcs, I may actually be losing weight! I'm waiting for the 992 GT3 brake lines and will post more details including the weight comparisons and the parts used.
Brackets, spacers and bolts that will be used:
Here's some initial pics from testing rear calipers and a used set of Girodisc rotors:
Overkill is an understatement if you're just looking for improvement for mountain road driving. A simple pad swap and better fluid would be an improvement.
Overkill is an understatement ... simple pad swap and better fluid would be an improvement.
Nah, that would be too easy! I do tend to overheat the brakes, not because I sit on them but more because I brake hard/late and trail-brake. I am sure if I was a better driver, the stock setup would be more than adequate.
As for the spacing, stock front caliper bolt spacing is 142mm, and the Porsche adapters allow the move to 225mm GT3 caliper bolt spacing. Stock and 992 rear caliper spacing are the same at 130mm. Rotor hat offsets on the Girodiscs are the same as stock so everything lines up and the rear rotors utilize the stock handbrake / pad spacing (180mm).
I don't see the point of this TBH, especially for a street car. Larger rotors are always nice, but not when you need to compromise with 20" rims and ultra low profile tires... Also 992 GT3RS has fairly large caliper pistons at the front, 32mm vs the 30mm on the 991 GT3. Since you also replaced the rear calipers, piston cross sectional areas of each axles are now quite a lot larger than the stock Carrera S setup. This is far from ideal for pedal travel if you don't upgrade the master cylinder as well, not to mention it changes the brake balance, which could be problematic for the PSM/ABS programming.
I think you would have been better off with the 997 350mm GT3/Turbo or 380mm 991 GT3 front calipers, which is what I used. Either options are PnP and most importantly they do not mess with the brake balance and piston cross sectional areas. Stock S rear calipers are fine--there is no need to upgrade even for a track build even. You could throw some 350mm 2 piece rotors if you got some extra budget--that's all this car need really.
I totally agree that there is no real point to this project.
This is more of a why not project and a challenge. I have done quite a bit of research on the potential issues / gotchas.
Here are some details that helped me decide to move forward:
Already had upgraded pads, GT3 master cylinder and Motul fluid, which helped some for the stock setup
Brake bias is maintained since both front and rear calipers are being upgraded with the 992 GT3 calipers
No need for ABS programming since I'm using steel rotors and related pads
Wheels and tires consideration - this definitely was a big decision going to 20's:
I can say that the car handling has improved significantly
No longer breaking the rear loose around hard turns / accelerating out
Front end even more planted - I installed the Elephant Racing front camber plates that helped with front end bounce
No noticeable change in ride quality (already heavily affected) - I installed a long time ago B16 PASM coilovers and DSC, GT3 sway bars, many other suspension upgrades
Kept the 20" rims/tires as close to the same dimensions / ratios as possible
Unsprung and rotating weight changes add up to a loss in weight - I will post a prelim table of changes - some values will need to be verified as they are web search info
Ultimately, if this experiment doesn't test out well, it can all be removed and go back to stock or as @cloud9blue said, go with a smaller setup.
Just for your calculations the fronts are 32/32/32Øx32mm and your rears are 34/34Øx32mm now. You had 36/44Øx32 and 28/30Øx32mm
Mike
OPS
Thanks Mike! This is perfect.
According to this info, the bias is shifted on the GT3's to be more even between front and rear. Will be interesting to see how that changes the braking dynamics.
Not sure if my calculation is correctly showing the total area in mm correctly, but at least the ratio will be correct!
Your car your money. That said I still think your wheel/tire setup brings a lot more downsides than anything you might have gained with the larger rotors.
Also you don’t need stock 992 lines or even the caliper adaptors. These 992 calipers look identical to the 991 ones so you can just use the flexible lines from Spiegler/Essex and the aftermarket adapters from Design911.
Your car your money. That said I still think your wheel/tire setup brings a lot more downsides than anything you might have gained with the larger rotors.
Also you don’t need stock 992 lines or even the caliper adaptors. These 992 calipers look identical to the 991 ones so you can just use the flexible lines from Spiegler/Essex and the aftermarket adapters from Design911.
Thanks! Let me know what downsides I may not be considering compared to the list above. I'm open to information.
I'm eliminating the hard line from the caliper to the brake line, so there's a brake line directly from caliper to chassis line. I bought a set from Essex, but they sent the wrong ones. I now have a set from HEL that is the same as the Spiegler but has the correct end to connect to the chassis hard line.
As for caliper adapters, yes, they are absolutely needed to get the calipers spaced out to support the larger rotors.
Hard to tell with your black caliper, but I think they look like they got the same bolt distance as the 380mm caliper on the 991. The 992 ones just sit a bit taller with a thicker mounting point. If you can share the exact part number you ordered, then I can cross reference with the ones I used.
As for the 20", unsprung weight is less of a concern when your rear tires are on sub 30 aspect ratio sidewalls. Even when I downsized my volvo wagon from stock 20" to BBS 19", I noticed noticable improvement in ride quality. And that's from 35 sidewall to 40. I bet 25 sidewall is not so much fun for Cali roads.
Yea, looks like those are the same dimensions, and about a hundred quid less.
I've driven about 800 miles and so far feels and handles better than the 19's. Not as bouncy and less roll, roads here are good for the most part, except the freeway concrete causes excessive tire/road noise in the cabin.
Ride quality has been reduced way before the 20" rims and tires! Exhaust, coilovers, suspension upgrades, seat change, lw flywheel, etc....
Finally had time to finish this and I'm still alive! Seriously though, the braking was good stock and now phenomenal with the upgraded setup.
I did make a mistake; the weights I had for Girodisc rotors were incorrect. I weighed them prior to the install and they are heavier, so no weight savings. I am over about 3 lbs per corner.
That being said, here are my observations after daily driving for a week:
Acceleration does not feel affected.
Front end bounciness is further reduced - after the coilovers and Elephant Racing camber plates there was a significant reduction in front end bounce.
Steering feels slightly heavier but in a good way, more planted.
Full braking is just awesome, stopping distances are reduced by a lot and the slight increase in rear bias keeps the car from leaning forward under extreme braking. Overall improved control of the car under braking.
Heat removal from this system is really good. After a drive, I can touch the caliper and rotor without searing myself, feels hot, but not painful. I'm sure I won't be doing that after spirited driving...
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Project 'Overkill' - Brakes Edition
