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Above: Porsche won 1st overall at the 1971 12 Hours of Sebring.

Porsche Factory Comments on Drilled Disks

During the [1971] Thursday practice session at Sebring, Porsche Panorama Tech Editor Roger Chaney had an opportunity to talk with a Porsche Factory Racing
Department Engineer. Highlights of the conversation with the engineer appear below.

Chaney: Many Porsche owners are interested in the 917 regardless of whether or not they are engaged in racing. What’s been done to the 917 over last year to improve it?

Porsche Rep: It is always important in racing to improve your car because if you stop making the car better, you won't win anymore. All last season we made improvements.
We made changes to the brakes to improve braking effort. Recently we attempted to make the unsprung mass of the car lighter by drilling the brake discs through the sides.
This is very important at courses like Sebring, which has a lot of bad lumps in the track. By the way, we found that by drilling the discs, the friction between the discs and brake
lining (pads) was better.

Chaney: Was this because of pressure relief between the pads and discs on brake application?

Porsche Rep: We presume so, yes. We also found that the lining wear was not increased by the holes, so we had only success and no evident disadvantages with this lightning.

Chaney: Is there anything on the cars here that is completely new?

Porsche Rep: The alloy is improved in the discs because we found that it is difficult with the drilled discs to prevent cracks without the new material. The brake discs will heat
up to 600 or 700C (close to 1100 to 1300F) during a race, which is dangerous for disc material in terms of cracking unless careful study is made. These studies led to the
new alloy discs with special heat treatment.

Cheney: A 911 owner shouldn't go out and drill his discs then, expecting to get better braking.

Porsche Rep: I don't think he would notice any improvement, no. Maximum temperatures you probably generate on a street 911 would be on the order of about 300C (about 600F
of less).

Note: It was found in practice runs at Sebring that the drilled front discs began to crack. The race was therefore run with undrilled front discs. The rear drilled discs performed
troublefree during the race.

I agree that street cars should not have drilled rotors, factory 911 turbo or otherwise. The brake dust they generate is unreal. My RS4 had the factory drilled rotors and there was a terrible noise at low speeds in stop and go traffic--and it did not matter if it was the day after I washed it. I have heard the same thing from Vette owners.

I have had better luck with slotted rotors, ran them three different times with no noise or excessive dust. I disagree though, I did feel the difference of running slotted rotors on a street car and occasional autocross (more bite). Anyone have experience with cryo rotors or is it just hype?

I tracked two Miatas for 5 years (one of them was V8 powered) and I always used solid rotors, as do almost all of the Miata track-rats.
They work great and are cheap to replace.
We left the slotted/drilled rotors for the Porsche (et al) crowd that were willing to pay the extra bucks for the looks.

84im wrote:I tracked two Miatas for 5 years (one of them was V8 powered) and I always used solid rotors, as do almost all of the Miata track-rats.
They work great and are cheap to replace.
We left the slotted/drilled rotors for the Porsche (et al) crowd that were willing to pay the extra bucks for the looks.

Same with me, I've tracked 2 CRX's, an Acura Integra, Fox Body Mustang, C5 Z06. I always ran solid rotors, the only rotor I ever cracked was on one that had been turned to true it up a bit, but it had been through hell and back too.

The discussions I've had with Danny (one of the owners) at Carbotech more or less spelled it out. The material used today, by Carbotech at least, doesn't have the significant off gassing that older brake pad materials did and thus giving up the friction surface to holes or slots is not necessary.

I've researched with other automotive engineers on the topic of slotted rotors and the evidence we found points to a few factors which Danny also agreed with.
If slotted rotors improve braking or wear then the brakes are likely being overworked/undercooled or the compound of the friction material is insufficient for the amount of heat produced.