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991.2 3.0 S Powerkit modified brake cooling

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Old 01-12-2018, 02:32 AM
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Tay101
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Default 991.2 3.0 S Powerkit modified brake cooling

According to Porsche's website, "The 3.0 S Powerkit also features modified brake cooling...". Does anyone know what this consists of? Does anyone know the part number? I emailed Suncoast and they couldn't find anything in their system.

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Old 01-12-2018, 08:50 AM
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If the car doesn't have PCCB's or doesn't have Rear Axle Steering, then there is a specific X51 retrofit kit which will come with new rear wheel carriers with ventilation openings and spoilers for cooling the rear brakes. That consists of wheel carriers, ducts, and hardware to attach it:


Hope that helps!
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Old 01-12-2018, 04:56 PM
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Originally Posted by SuncoastParts View Post
If the car doesn't have PCCB's or doesn't have Rear Axle Steering, then there is a specific X51 retrofit kit which will come with new rear wheel carriers with ventilation openings and spoilers for cooling the rear brakes. That consists of wheel carriers, ducts, and hardware to attach it:


Hope that helps!
Thanks for the quick response Suncoast.

Are you saying getting rear axle steering automatically gets you the modified brake cooling even if you don't get the Powerkit? What is the cost and part number for this kit?

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Old 01-12-2018, 05:59 PM
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As we understand it, yes. So if you have PCCB's or Rear Steering, then rear brake cooling is added to the car. If you don't have X51, PCCB's, or Rear steering.........there isn't an exact retrofit kit for all of this hardware. But we can piece it together. Not cheap! I'll send you a PM with details.
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Old 01-12-2018, 07:09 PM
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Originally Posted by SuncoastParts View Post
As we understand it, yes. So if you have PCCB's or Rear Steering, then rear brake cooling is added to the car. If you don't have X51, PCCB's, or Rear steering.........there isn't an exact retrofit kit for all of this hardware. But we can piece it together. Not cheap! I'll send you a PM with details.
Does that mean the carrier itself is different from the non RWS/GTS models only because of the mounting points for the brake ducts or is the carrier structurally stronger?
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Old 01-12-2018, 07:41 PM
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Funny thing is, it seems like the base 991.2 Carrera brake system's only lack is adequate heat management. So is that rotor size or cooling directed at the rotors? There used to be some pretty great kits made for torsion bar 911s and 914s to improve front brake cooling. I wonder if a similar idea would suffice here. PeteVB, what say you?
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Old 01-13-2018, 07:40 PM
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Originally Posted by stout View Post
Funny thing is, it seems like the base 991.2 Carrera brake system's only lack is adequate heat management. So is that rotor size or cooling directed at the rotors? There used to be some pretty great kits made for torsion bar 911s and 914s to improve front brake cooling. I wonder if a similar idea would suffice here. PeteVB, what say you?
I agree that the base Carrera's brakes would be solid if you can add enough cooling. The trouble is that you can nearly always say that, can't you? A larger rotor not only increases thermal mass for better single stop performance, it also increases surface area and rotor speed for better cooling, so it's double benefit, and hence the desire to more cooling likely end up driving rotor size more than mass.

Stepping back 330 mm is still a big rotor- until recently LeMans cars weren't running much bigger. It's certainly very big for the rear, with the same disk dimensions as the S or GTS (though with significantly smaller pads). Given those generous disks I'd expect that especially with good pads you'd be fine on rear temperature unless you're really leaning on traction control.

The base fronts however were not upgraded from the 991.1, and are also 330mm. The S/ GTS meanwhile went from 340mm to 350, so the fronts seem like they got slightly shorted. That said they use the same size pad as the S/GTS, and 330 x 34mm was deemed sufficient for the 408 hp 997 GTS and the 420 hp 996 Turbo. I don't think of the 997 GTS as under-braked, which seems to confirm the suspicion that the rotor's sufficient if you can get enough air to it.

Porsche does fit good brake ducts standard (Porsche calls them spoilers up front). However they might not be the best brake ducts. If I had a base 991 I'd be tempted to see if the two piece GT3 front brake spoilers fit. They look superior to the Carrara's 1 piece design to my eyes (Carrera first, GT3 2nd). If those would fit (and work well with the stock underbody) they might give a little more headroom.


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Old 01-13-2018, 09:05 PM
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^ Good info, and perspective.

If I had a base Carrera or T with the standard brakes, I'd be very interested in more aggressive front brake cooling—whether trying to fit GT3 or making new pieces that do something similar. Seems like a job for a smart aftermarket company, whether TPC or AWE or? This, along with a larger front rotor on an aluminum hat with a spacer to move the caliper out might make for a very attractive and cost-effective upgrade for these cars. Hmm...
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Old 01-14-2018, 01:08 AM
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Originally Posted by Petevb View Post
I agree that the base Carrera's brakes would be solid if you can add enough cooling. The trouble is that you can nearly always say that, can't you? A larger rotor not only increases thermal mass for better single stop performance, it also increases surface area and rotor speed for better cooling, so it's double benefit, and hence the desire to more cooling likely end up driving rotor size more than mass.

Stepping back 330 mm is still a big rotor- until recently LeMans cars weren't running much bigger. It's certainly very big for the rear, with the same disk dimensions as the S or GTS (though with significantly smaller pads). Given those generous disks I'd expect that especially with good pads you'd be fine on rear temperature unless you're really leaning on traction control.

The base fronts however were not upgraded from the 991.1, and are also 330mm. The S/ GTS meanwhile went from 340mm to 350, so the fronts seem like they got slightly shorted. That said they use the same size pad as the S/GTS, and 330 x 34mm was deemed sufficient for the 408 hp 997 GTS and the 420 hp 996 Turbo. I don't think of the 997 GTS as under-braked, which seems to confirm the suspicion that the rotor's sufficient if you can get enough air to it.

Porsche does fit good brake ducts standard (Porsche calls them spoilers up front). However they might not be the best brake ducts. If I had a base 991 I'd be tempted to see if the two piece GT3 front brake spoilers fit. They look superior to the Carrara's 1 piece design to my eyes (Carrera first, GT3 2nd). If those would fit (and work well with the stock underbody) they might give a little more headroom.


Although the diameter of the base 991.2 brake rotors did not change from the 991.1 they were enhanced by making them thicker, going from 28 to 34mm. That made them the same size of the 991.1 S front rotors. And the S rotors in the 991.2 retained the 991.1 thickness, but went up in size from 330 to 350mm.
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Old 01-14-2018, 04:36 AM
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The part number you are looking for is 991.044.100.14



The above photo - left = rear OEM brake pad, centre = front OEM backing plate, right = front OEM brake pad (after two full days of sprint racing)

The photos show pads from a 991.2 SX51 in a poor state of repair (50% left) cracks are visible along with missing friction material. The backing plates on the rear and front pads are detached due to heat. In contrast the brake rotors remain in good repair.

The rear axle brake ventilation kit is nice to have (basically two air deflectors), however pads with higher operating temperatures are a better solution (plus a brake fluid capable of higher temperature operation).

Its fair to say the front pads in the base model (four pot system) would be in a far worse state of repair than the pads from the S (six pot system) in the scenario above.

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Old 01-14-2018, 12:28 PM
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Originally Posted by Valvefloat991 View Post
Although the diameter of the base 991.2 brake rotors did not change from the 991.1 they were enhanced by making them thicker, going from 28 to 34mm. That made them the same size of the 991.1 S front rotors. And the S rotors in the 991.2 retained the 991.1 thickness, but went up in size from 330 to 350mm.
Good call, the 991.2 base Carrera used 997S size rotors while the 991.1 were thinner as you point out. As cooling doesnít increase much as the rotor gets thicker (vs wider) that would also support the theory that cooling is the weaker area.

Thinking about this further though I should add to my previous statement. Iíll note that I got the 981 Boxster Spyder brakes to smell on the street when pushing, and those are larger at 340 x 34. Given thatís a lighter car that probably canít deploy as much power one assumes the 991.2 Carrera will be worse. That said I considered the 981 Sypderís brakes well sized for the street. On a street car Iíd personally rather have smell brake pads (very occasionally, assuming they never fade) than carry a bunch of extra unsprung, rotating weight all the time. The 380mm disks from my GT4 were frankly overkill in most situations, and Iíd have been quicker at the autocross the the Spyderís smaller hardware. So from that perspective Iíd be looking to add cooling to the base Carrera.

As track use comes into play, however, my perspective shifts. There you can virtually never have too much brake or cooling, and oversized is exactly what you want. If nothing else it helps you limit pad swaps, etc. Porsche increased rotor diameter by 15% over the GTS in the GT4 in order to make the brakes track worthy, and the brake pads grew by a similar amount. The rear brake ducts are nice (the question is if the rear mounting points for it exist in the base Carrera) but for heavy track work best case youíd still be eating pads at an extreme rate. If thatís the plan for a base Carrera/ T Iím not sure what Iíd recommend... Maybe a brake swap from a GT3? Or order PCCBs and then swap the rotors for iron (assuming replacement after 30-50 track days doesnít fit your budget)? The question is largely one of usage and expectations. Occasional track use Iíd swap pads, change fluid regularly and upgrade cooling, expecting to watch temps and go through pads quickly. From a heavy track use perspective, however, one needs to say 330mm looks pretty small compared to what Porsche deploys for that use (380mm with big pads at all 4 corners).

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Old 01-14-2018, 02:41 PM
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Has anyone tried adding the GT3 upper ducting, the one with the green arrows, onto a S or GTS? If so does anyone have the part number? It looks like it might overlap the stock S ducting but that's nothing a Dremel wouldn't fix.
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Old 01-14-2018, 10:50 PM
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Originally Posted by Petevb View Post
I agree that the base Carrera's brakes would be solid if you can add enough cooling. The trouble is that you can nearly always say that, can't you? A larger rotor not only increases thermal mass for better single stop performance, it also increases surface area and rotor speed for better cooling, so it's double benefit, and hence the desire to more cooling likely end up driving rotor size more than mass.

Stepping back 330 mm is still a big rotor- until recently LeMans cars weren't running much bigger. It's certainly very big for the rear, with the same disk dimensions as the S or GTS (though with significantly smaller pads). Given those generous disks I'd expect that especially with good pads you'd be fine on rear temperature unless you're really leaning on traction control.

The base fronts however were not upgraded from the 991.1, and are also 330mm. The S/ GTS meanwhile went from 340mm to 350, so the fronts seem like they got slightly shorted. That said they use the same size pad as the S/GTS, and 330 x 34mm was deemed sufficient for the 408 hp 997 GTS and the 420 hp 996 Turbo. I don't think of the 997 GTS as under-braked, which seems to confirm the suspicion that the rotor's sufficient if you can get enough air to it.

Porsche does fit good brake ducts standard (Porsche calls them spoilers up front). However they might not be the best brake ducts. If I had a base 991 I'd be tempted to see if the two piece GT3 front brake spoilers fit. They look superior to the Carrara's 1 piece design to my eyes (Carrera first, GT3 2nd). If those would fit (and work well with the stock underbody) they might give a little more headroom.


Originally Posted by CarreraFahrer View Post
Has anyone tried adding the GT3 upper ducting, the one with the green arrows, onto a S or GTS? If so does anyone have the part number? It looks like it might overlap the stock S ducting but that's nothing a Dremel wouldn't fix.
Great find!

I would be interested in the GT3 ducting as well.
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Old 01-15-2018, 12:06 AM
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The part number you are looking for is 991.044.100.14

There are a number of ideas conflated in this thread. The bottom line is a car is only as good as its brakes - the ability of the brakes to deal with heat is given by the specific heat capacity of the material used to construct the brake rotor and the ability to shed heat is driven by the thermal conductivity /conductance of the material in question.

The underbody airflow of Porsche sports car is heavily modelled - and its important to understand the cooling mechanisms for the brake system is equally heavily modelled by manufacturers and suppliers alike. Parameters such as the air pressure under the wheel arches is an important consideration, as is how air is both extracted and pushed onto the rotors. Basically, swapping to a GT3 duct may not deliver a better outcome and could deliver a worse outcome.

Consider the following hypothetical scenario - a 1500kg car brakes once from 200kmh to 100kmh (and to 0kmh)

Brake set 1 - total mass of rotors, 34kg - cheap iron. Change in temperature of brakes is ~ 128 degrees celsius (and 170 degrees celsius)
Brake set 2 - total mass of rotors, 34kg - track formula. Change in temperature of brakes is ~ 102 degrees celsius (and 136 degrees celsius)
Brake set 3 - total mass of rotors, 20kg - carbon ceramic. Change in temperature of brakes is ~ 52 degrees celsius (and 58 degrees celsius)

Now, lets drop the mass of Brake sets 1 and 2 to 28kg
Brake set 1 - total mass of rotors, 28kg - cheap iron. Change in temperature of brakes is ~ 155 degrees celsius (and 207 degrees celsius)
Brake set 2 - total mass of rotors, 28kg - track formula. Change in temperature of brakes is ~ 124 degrees celsius (and 165 degrees celsius)

From a technical perspective large carbon ceramics are the go (assuming you are prepared to accept the replacement costs and you live in a land free from small stones). Next cab of the rank are large (surface area), heavy, track formula steelies.

Superimposed on this is the quality, thickness and surface area of brake pads. Worn (<50% thickness of friction material) conduct heat rapidly through to the brake fluid. Thus repeated braking from high speeds with smaller brake rotors and worn pads will trigger brake fade (long pedal) and can result in failure.

Thus its a simple story and a well understood one at that - big brake rotors with fresh high temp pads and high- t brake fluid trumps all else (the brake ducts are already there and the deflectors will make the very smallest of difference). The answer with something like the Carrera T is PCCB (almost a no brainer). If you are in the base Carrera, upgrade the pads and fluid before even thinking about big brake kits (particularly if the car is largely used on public roads).

Last edited by RRDnA; 01-15-2018 at 10:33 PM.
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Old 01-15-2018, 02:03 PM
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Originally Posted by RRDnA View Post
Consider the following hypothetical scenario - a 1500kg car brakes once from 200kmh to 100kmh (and to 0kmh)

Brake set 1 - total mass of rotors, 34kg - cheap iron. Change in temperature of brakes is ~ 128 degrees celsius (and 170 degrees celsius)
Brake set 2 - total mass of rotors, 34kg - track formula. Change in temperature of brakes is ~ 102 degrees celsius (and 136 degrees celsius)
Brake set 3 - total mass of rotors, 20kg - carbon ceramic. Change in temperature of brakes is ~ 52 degrees celsius (and 58 degrees celsius)
Iím not sure how youíre getting the numbers above. Would you mind explaining your process?

The specific heat of cast iron is .5, while SGLís carbon ceramic rotors are .8. Given this the heavier cast iron rotors actually have more thermal mass, and would be expected to heat less than the ceramic rotors in the example above over a single quick stop. Ceramicís advantage is in better cooling and higher peak operating temperatures. However it gains heat as fast or faster in the first place given its low mass, so your example doesnít seem to compute...?
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