ELUSIVE

I'm sure this has been asked before, but are the cross drilled rotors that come on Porsche's cast with the holes or are they drilled after the fact?

Thanks,
Stacey

Chupa

They are cast in. Drilling afterwards disrupts the grain structure making the rotor very prone to cracking from thermal cycling.

ELUSIVE

That's what I thought as well.
A guy on another forum is saying that he knows for fact that no rotors are cast with the holes in. Does anyone know where to purchase rotors that are cast with the holes?

Thanks,
Stacey

NetManiac

If you are looking for Porsche OEM rotors you can get them from http://www.group9motorsports.com. He also carries Frozen Rotors for most P-cars. If it's for a different make I dont' know where to send you.

Tool Pants

The rotors are made by Zimmerman, and you can get them solid or with holes.

Fletcher

Jeff, are they cast or drilled. I understand zimmerman makes both in some instances??

Tool Pants

I do not know why you understand that.

This subject and other performance modifications were cover at the tech session last Saturday, including the flywheel. The presenter coverd "drilled" sloted and frozen rotors.

NetManiac

Tool Pants: You know not everyone on this board lives within driving distance of San Jose, right? Is there someplace we can go to learn what the "presenter" presented? Like the Rennlist tech area? Or maybe you can post the transript here since this thread seems to be on the same subject?

Looks like you covered flywheels and exhaust also. I would interested to read the opinions of the "presenter" on those subjects as well.

Tool Pants

I answered a guestion from Fletcher from Salida, California. He is not that far away. We have people that come to our work on cars days, from all over.

If you want to know about the Monster Boxster then look here. There is no transcript. It was a tech session that you go to, or not. http://www.renntech.org/forums/index.php?showtopic=2766

I have to set this suff up. Then a few dozen people want to know when lunch is in the middle of the tech session - so I have to take care of that.

Fletcher

Actually Troutman told me that zimmerman was making cast "holed" rotors now but wasn't sure about Boxster non-S application. They do quite a bit with rotors for Porsches. As stated not all can attend these tech sessions. So we appreciate the teaser pictures and all but humor us once in a while ok.
Thanks for your input...!

ELUSIVE

Does anyone have a direct contact for Zimmerman rotors?

Thanks,
Stacey

KevinC - SJ,CA

Although the holes are produced during the casting, they still promote cracks and grooving of the rotors and discs. I think that any benefits of the holes are marginal at best. I wish I could easily find unholey rotors for my S. I would not recommend that someone convert a stock Boxster to rotors with holes unless they are doing it purely for the looks.

Here is what the holey rotors look like after some track use:

Alan Herod

Kevin,

The significant ridge at both the outer edge and inner edge would suggest that the rotors were worn below their wear limits. I have old rotors off the track car showing the same cracks in both solid and slotted vented rotors. It is interesting that the cracks always form about the holes. As far as the viability for a track event with the rotor pictured, it would probably be unacceptable for wear, but not for cracks. At tech we advise to watch more closely and change rotors when the cracks begin to connect.

JeffES

Kev,
It's a trade off - perforations generally allow for slightly quicker wear, but solid rotors simply don't cool as quickly as do perforated, nor do solid rotors "shed" excess materials (gasses and some solids) as quickly as do perforated rotors.
In simpler terms, solid rotors would tend to last longer. Perforated rotors tend to provide better braking (esp with heavy brake use).
J

JeffES

BTW, the previous poster is correct. The perforations are cast in. The slight beveled edge - a kind of chamfer - is then machined at each perforation, along with final "truing" of the entire rotor.
J