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Old 03-15-2007, 10:50 AM   #48
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Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
Some more info found on another forum posted by a guy who works for Brembo -
However, one intersting item is that all of our X-drilled holes are exactly that....drilled.....even the Porsche ones. Its a bit of an urban legend that Porsche "casts-in their holes" for strength. Truth is, when I started with Brembo I thought the same thing. I mentioned it to our Italian resident Applications Engineer. I was kinda surprised myself. He laughed and added, "People seriously think we cast in all of the holes? Wow, I'd love to see the mold for that! No, actually they are all drilled and chamfered post-casting. "
spoke with one of the Apps Engineers from Italy and he confimred what was said. The rotors are designed by Porsche and cast/machined by SHW. Brembo supplies the Caliper and the knuckle, and assembles the wheel end (thus the reason for the wheel end assy on my desk).

He said that in the case of Porsche, even the caliper is a build to print. In other words, Porsche Engineering designs all of the components, but has manufactuing done by SHW and Brembo.

He also added a few comments/corrections on the rotor design itself. The "half-vanes" are there soley for preventing crack propagation. The holes are not actualy through the vanes (something we verified with a paper clip with the one on my desk). The holes follow the same curve as the vanes and are placed extremely close to the vanes, but don't actually go through the vane itself. Finally, he added that even SHW does not cast the holes in, they are indeed machined and chamfered. he said he is not aware of anyone who manufactures cast-cross-drilled rotors on a mass-production level.
And in response to the question - "what is your opinion on X Drilling of rotors?"
My personal opinion is with today's materials its mostly for bling. there are some slight benifits to it, but there are also some negatives. There have been Brembo/Porsche tests to show that x-drilled rotors increases first effectiveness in wet conditions. Assuming there is enough mass for thermal capacity of the application, X-drilling can save a slight amount of weight (although any unsprung, rotating mass savings help) and offer small increases in cooling speed. However, they are prone to crack more, especially propagating from the drilled holes. This can be accounted for with a proper rotor design (i.e., pillar and hole location/orientation) to prevent small cracks from propagating all the way to the disc edge. If the rotor is designed correctly and sized properly for the application cracking is minimal. That being said, many designs on the market (I won't name any specifically) arent designed properly (arrangement to prevent crack propagation), machined properly (poor or no chamfering), and are under-sized for the application (thermal mass). This is especially true of those popular in the ***** community.

Now, with all of the previous being my personal/professional opinion, Brembo understands that there are both advantages and disadvantages to X-drilled rotors. We leave it to our customers discretion as to which is used (drilled/slotted/solid-faced). In most OEM situations, it comes down to Marketablility.
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