Drilling Rotors

[andycook]

Has anyone here ever drilled their own rotors? We do this on our Pro-4 circle track car and I thought about doing it to my SC. Anyone ventured down this road before?

[ChrisBennet]

It makes them more likely to crack and they won't pass tech if you want to do PCA Driver's Ed with them. It's just a bad idea.
-Chris

[andycook]

Do aftermarket drilled rotors pass tech?

[Dantilla]

Look for rotors with casted holes instead of drilled.

[ChrisBennet]

Originally posted by andycook
Do aftermarket drilled rotors pass tech?

They didn't used to. In the last year or two the tech form for North Country Region was shortened so that language may have been dropped but the reason it was there is still valid. (NCR is my region and we are next door to Andy.)
The SC rotors are thin and not meant to be drilled. The "drilled" rotors that you see on Porsches actually have the holes cast into them. The aftermarket racing rotors (Alcon, etc) are generally a thicker rotor. The problem with the thin drilled rotor on a heavy car is that they can fail in a big way. The holed rotors all crack (drilled or not) but the cracks propagate slowly in the cast hole flavor.
AFIK the holes in rotors solve a problem that doesn't exist much anymore with the newer brake pad compounds. That said, I might consider them for a wet or muddy rally. Targa Newfoundland anyone?

Do a search of "drilled rotors" and you'll find more info.
-Chris

[Wil Ferch]

Don't believe you can get them that way as aftermarket for Carrera sized rotors.

Slotting might be acceptable, yet these too introduce stress risers and can crack later.

Thought....how about drilling holes but polishing/champfering each hole ( labor intensive) to lessen the tendency to crack ?

Wil

[andycook]

Thanks for the input guys. Yes, Chris, we are almost neighbors, and it would be the NER that I would be participating with (I hope).

As for Will's suggestion, we used a 45 degree chamfer mill to chamfer each hole in our rotors. Very time consuming yes. But hey, Maine winters are Looooong! Call it luck, but I never cracked one. Warped the S**t out of them due to heat, but never cracked one.

Chris, If I join the NER are there rulebooks that I can get? Do the rules follow each event or are they like circle track where they vary from each track?

My goal is to make a trip to Lime Rock and Watkins Glen next summer with my car to try it out. Just for fun. I have alot to do, but again, Maine winter really bite!!! I have plenty of time.

[dtfastbear]

Drilled rotors on a Carrera are a "looks only" modification. They don't add any measurable performance advantage, cooling or otherwise, to the braking system unless you're driving in mud, perhaps.

You can buy drilled rotors for a Carrera - but they should more accurately be called "holed rotors" because as Dantilla mentions, the holes are cast into the rotor, not drilled into a solid rotor.

All this being said, if you have "open" wheels that make the rotors visible, drilled rotors look really good and might be worth the extra bucks for that reason alone.

Dean

[ChrisBennet]

Originally posted by andycook
Thanks for the input guys. Yes, Chris, we are almost neighbors, and it would be the NER that I would be participating with (I hope).

As for Will's suggestion, we used a 45 degree chamfer mill to chamfer each hole in our rotors. Very time consuming yes. But hey, Maine winters are Looooong! Call it luck, but I never cracked one. Warped the S**t out of them due to heat, but never cracked one.

Chris, If I join the NER are there rulebooks that I can get? Do the rules follow each event or are they like circle track where they vary from each track?

My goal is to make a trip to Lime Rock and Watkins Glen next summer with my car to try it out. Just for fun. I have alot to do, but again, Maine winter really bite!!! I have plenty of time.

Not to knock our NER neighbors (North East Region, mostly MA) but you should be joining NCR (North Country Region, mostly NH). We are one of the friendliest if not the friendliest region and we have a track schedule that includes Lime Rock (which NER didn't last I knew). JD Power surveys of the last 9 years has listed NCR as the best PCA region in the US. (OK, I made that part up.)
In the interest of full disclosure, you live in Down East Region - another great bunch of guys (and girls).
-Chris

[movin]

Can't rotors be drilled then each hole stress relieved?

[Bill Verburg]

There are no 20mm rotors w/ cast holes, for good reason, they are already undersized. I believe that Brembo may have a 24mm rotor w/ cast holes in it's catalog, but they are very difficult to get a hold of. Again these are undersized to begin w/ so removing mass just makes them get hotter that much quicker.

ANY rotor solid, drilled or slotted will crack if it gets hot enough and is stressed enough.

The stouter 32mm 930 rotors are over sized for use on a light car and can afford to give up some mass. The flimsier 32mm Colmans probably cannot.

As Chris mentioned the original reason for the drilling besides weight was to provide a path for out gasssing from old style pads. Modern pads don't have that problem to as large an extent.

You can minimize stress risers by chamfering but they are still there in the internal structure of the rotor.

There is a down side to slotting in the reduced pedal feel that often accompanies them, they wil always chatter a bit more than solid or drilled.

[Oldporsche]

I've drilled them. I don't really like to, and have slotted some ala '78 930 style. The holes provide some compression area for air when applying the brake. Also somewhere for the water to go when its wet.

I agree in that our rotors are probably not thick enough to safely drill. If you must drill, I would champfer the holes with a rounding type center drill. You can find them at a machinest supply store.

Good luck,
David Duffield

[82SC]

interestingly...the new PCCB brakes are drilled after the ceramic rotor is made...

I guess some property in ceramic allows drilling raterh then casting...

I can imagine it'd be pretty hard to cast a ceramic rotor with holes

[randywebb]

still there in the internal structure....

think about how metal looks microscopically -- the drill is cutting thru (or next to) the grains. When a piece is made with the holes in it, the grains 'move' to compensate. My bomb-making materials scientist buddy can explain this a lot better, but that gives you a start.

This also explains why the hype about 'billet' is just hype (unless you are comparing it to a stamped piece).

[Harlan Chinn]

Only if you have the patiences and or a computerized mill.