carlitox33

My ´86 carrera rotors seem to be quite bent and worn out (both mechanic and vibrations tell me so). I am considering going for new rotors, and have seen some drilled out rotors specially made for 3.2 911´s.

Does someone have experience on the advantages/disadvantages of drilled rotors vs. solid rotors? All 4 will be replaced.

Thanks in advance

BER

Carlos,

If you have "bent" rotors, you must be doing some heavy braking!

I have used solid and slotted rotors on my 911's (1984 & 1977). I have avoided drilled rotors, because some drilled rotors are prone to develop hairline cracks under hard (i.e. track) usage.

I have friends in PCA that have used drilled rotors at Driver's Education events. Some of them have discovered the hairline cracks after a couple of events. I have been using slotted rotors for a couple of years in combined street/track usage and have experienced no rotor problems.

On the other hand, if you are only using your car on the street for "normal" use, drilled rotors should be OK.

Regards, Bruce

Bill Gregory

Carlos,

If your usage is street non-track usage, stick with the factory vented rotors, as they work fine. The next choice would be slotted rotors, which retain the heat sink capabilities of the solid vented rotors but have slots milled in them to help keep gases and water away from the face of the brake pad and rotor. Slotting is less invasive to the metal of the rotor too. There are two varieties of so called "drilled" rotors, those that have the holes cast in when manufactured and those that are solid rotors that have been drilled. Porsche rotors have cast-in holes. Unless you are flush with money, avoid the drilled rotors, as they can (and do) develop cracks between the holes quickly, which means replacement. The rotors with cast in holes will eventually develop cracks between the holes, however, it takes longer. Some people use cryogenically-treated rotors for longer life.

Jgordon

I'll put to use some newly acquired knowledge.

Rotors that were cast solid and then drilled have a much shorter life span than rotors with the holes cast in them -- the metal molecules set up in the casting process, and when drilled, they lose the strength that they gained in the casting.

I think the rotor hierarchy (brands aside) goes:


1. Cryogenically treated vented/cast drilled rotors

2. vented or slotted rotors

3. Aftermarket drilled rotors

4. solid rotors (these will most likely last a while, but not perform as well as some of the other heat dissipating rotors).

Damn, I said "rotors" a lot.

Rick Deman at Deman motorsport <a href="http://www.demanmotorsport.com" target="_blank">www.demanmotorsport.com</a> supplied me with my limited knowledge. Give them a ring, they'd be happy to get you some appropriate pieces.

Clark Griswald

Carlitox,

You didn't say how you plan to use the car, but from your description I am assuming it is a street car. You also didn't say why you want drilled rotors.

As stated correctly above, drilled rotors get a bad rap because they have shown a greater propensity to cracking then solid or slotted rotors. Cast holes reduce but do not eliminate this.

What usually doesn't get mentioned in these discussions is that this only happens to rotors that are repeatedly stressed to their limits under extreme racing conditions. And then it only happens sometimes.

Normal street cars never see these extremes and operate just fine with drilled, slotted, cast and solid rotors. Remember that none other than Porsche sees fit to deliver their cars with drilled rotors.

Drilling advantages are:

- superior wet braking performance
- improved appearance
- allows gases released from the bonding agents in the pads to escape, reducing skating
- reduced weight

The weight reduction is minor and relevant only for race cars. The skating problem only happens under operating extremes, again only relevant to race cars. Wet braking will be improved but is generally not considered a problem even with solid rotors.

Which leaves appearance. Drilled rotors do look great.

So the bottom line is - if you want the drilled rotors because they look good then go for it. They will last and peform safely.

Bill Gregory

[quote]<strong>I think the rotor hierarchy (brands aside) goes:.

1. Cryogenically treated vented/cast drilled rotors

2. vented or slotted rotors

3. Aftermarket drilled rotors

4. solid rotors (these will most likely last a while, but not perform as well as some of the other heat dissipating rotors).</strong><hr></blockquote>

For clarity, most 911's after the late 60's have vented rotors. That's a rotor with air venting ribs in between the two rotor faces. A vented rotor is not the same as a slotted rotor. A slotted rotor has 3-6 slots in each rotor face, typically on a vented rotor. You rarely, if ever, see solid rotors on Porsches. And a solid rotor is exactly that....a solid hunk of metal with no venting. A 2002 VW Jetta, for example, has a solid rotor on the rear brakes.

Chris Blum

Regular vented rotors are just fine unless you are doing a lot of heavy braking over several laps. Save the money. <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

t.p.

i've read that cryogenics does not improve a rotor.

Chris Blum

You hear some people swear by those "frozen" rotors, but the whole things seems kinda snake oily as if there is some residual "coolness" that magically stays in the rotor. Or maybe, its the fact that, living in MN, I tend to shy away from anything frozen when possible.