Cross drilled rotors.....a design flaw?

[ssp996]

How about the Porsche RS Spyder?

No slots or cross-drilling.

How does slotting or cross-drilling affect integrity of those rotors? Maybe in the next decade, those 2 GM engineers will write another white-paper on them... if GM is still around by that time...

///Michael

[ssp996]

Did anyone read an article a few months back in C & D magazine where they compared braking distances and fade resistance of many different cars including a base 997, a 997S, and 997 with the PCCB. They couldn't make even the base 997 fade as I recall. And the PCCB were not that much better considering the costs. Worth a read

[violaGT3]

Did anyone read an article a few months back in C & D magazine where they compared braking distances and fade resistance of many different cars including a base 997, a 997S, and 997 with the PCCB. They couldn't make even the base 997 fade as I recall. And the PCCB were not that much better considering the costs. Worth a read

Well it would figure as a toe to toe comparison with other cars Porsche has the most capable brakes I have seen less a $130k Merc. My 03' Stillen Altima 348WHP had the stock brakes, I believe they were 2 pot calipers and 12.5" rotors. I believe that is the same setup on a Chevy Astro??? I sold it due to it needing to have a intermediate shaft it would jump nearly 3 feet to the right and then catch and straighten out on a hard launch. Great car but not designed to have that much power. The only fair test for Porsche to be compared to is the Exotics and maybe a AMG or . . . . . a Vette. Yea I know I am not a big fan of them which is why I have never owned one but they are improving by leaps and bounds and from what friends of mine in Europe tell me the new Z06's will embarrass most 911's, yes including turbo models. :o

Have a looksie: Turbo

:eek: GT3

Now if they could just correct the gearing and make it is little less nausious to drive. . . . Naa I'd still want my Baby!

Edited November 18, 2008 by ViolaGT3

[violaGT3]

Hmm, I would have to say that there is a little bit about Porsches(911) being engineered to do 180mph, and Z's set at about 150mph. I would think that sub 12" rotors on a 3300# car would desintigrate after s short time on the Autobahn. Wonder if the specs are different in Europe or Japan? That's an odd comparison. in my book of performance cars, a 350Z you would not find, nor it's competitor the Crossfire or the Z3/4. While they are sporty and 15-26 year olds love them you would more then likely destroy one of them if you did track it(consumer cars). My thoughts on the brakes for 911's is simply engineered to take what you throw at it. Switzerland, Germany, USA, Italy, Doesn't really matter which one. I have run into a few hills in a rental BMW 323 in Garmisch Germany before thart would have really appreciated Porsche brakes.

A short digression...

Well, back in the day, I had a 2003 350z Track model and my friend had a 2003 350z Touring model. My Track model had factory 12.75" rotors front and rear w/ Brembo 4/2 pot calipers while his Touring model had those sub 12" rotors w/ 2 pot sliding calipers.

On our first DE, he had braking issues (heavy pad and fluid fade) while mine held up ok except for the uneven deposition I got on the rotors. I simply had my rotors turned to remove the deposition while he upgraded to a 13" Stoptech BBK. A few DE's later, hairline cracks started developing on my solid 12.75" rotors. At $500 per factory rotor, the 350z Track model quickly lost its allure for a cheap track platform.

Granted that I had the rotors turned to remove the deposition, they were still w/in spec. But if I could crack solid rotors in a few DE's, just think what would happen if I slapped aftermarket cross-drilled rotors w/o increasing rotor width or diameter...

///Michael

Here's a 350 that could of used some upgraded brakes. check out the speedlimit sign at the crash site. :huh:

http://www.youtube.com/watch?v=Nc0V7dHKgY0

[td873]

Two GM engineers tested 2-3 cross-drilled braking systems and 2-3 solid-face braking systems. The pictures blurred anything on the rotors that could identify the braking systems they tested. It's a 28 page analysis/report with quite a bit of technical mumbo-jumbo.

They made a few observations (including the obvious of cracks developing around the holes), but the one that pertains to my reply is that cross-drilled rotors do improve brake cooling over solid-face rotors. Furthermore, the cooling rate increases as speed increases.

Of course, rotor design also plays an important factor. It is possible to put too many holes in a cross-drilled rotor or place them ineffectively.

The SAE article is locked w/ DRM on my personal laptop. If anybody is interested, then I'll also summarize the other observations that they noted in their conclusion if I get some time this evening. In the meantime, somebody else on another auto forum has read the same paper; you can read his comments as well if you're bored: linky, linky

I just stumbled on this thread, so I am going to reply, although a little late ;)

I suggest folks read this themselves: it is HIGHLY biased towards cross-drilling. AND it does not account for slotted or dimpled rotors or other engineered solid rotors. ONY completely solid ones (see the picture on page 24) and p.23 where they admit they didn't even look at slotted or dimpled rotors). It is unclear what types of venting/vaning the solid rotors they used have - if any!

Because of these fundamental issues, it is easy to find snippits favorable to cross-drilled rotors in the article - but only as they are compared to generic solid rotors. Again, ONLY completely solid rotors, and not race rotors with slots / dimples / vanes / vents, etc. [Note that there is plenty of discussion about the vaned design of the x-drilled - but almost no discussion on the type or design of the solid rotor. Clearly a Brembo (or other) solid rotor will operate better than less "engineered" models.] Despite the fact that they used junk solid rotors, there were still a number of points favorable to the non-crossdrilled rotors they tested!

High Performance Wear Test - conclusion: higher apparent friction levels for non-crossdrilled rotor during the 450 deg C wear test.

High Speed Abuse Test - brake system 3b had higher brake system output with smaller diameter, non crossdrilled rotors than system 3a with the larger diameter crossdrilled rotors.

Life - adding crossdrilling to the rotor design "reduces its fatigue life." This will occur at a lower number of heat cycles than ... a solid rotor. [i.e., cross drilled rotors die faster]

[There are others, but these are kinda neat]

Also, keep in mind that their test does not accurately represent real world use. For example, the tests were not dramatically affected by pad build up in the holes. This will severely change the results, since the ENTIRE premise of the article is that the holes help. In fact - they indicate that OVER 90% of the hole will clog under use! [brake system 1, full. Brake system 2, 90%.] They also state that this can have really bad results. [This also illustrates that new pad technology does NOT need the holes for venting gas.]

I also direct your attention to one of the most important conclusions - design affects performance. System 1 and 2 showed better performance with x-drilled, but system 3 showed better performancewith solid. But, what would happen with a properly designed rotor?

The closing statements of this article details the many negative affects of using cross drilled rotors. But I want to emphasize that the data presented is only a few data points regarding completely solid vs crossdrilled rotors. NOT crossdrilled vs track/slotted/dimpled/etc rotors.

Also, please refer to the more recent technical articles on the SAE site. There is a great one on Race Braking Technology (ca 2008). That one states you can improve brake cooling "through rotor design, cooling ducts ... and in some cases rotor crossdrilling can improve cooilng, but at the expense of lining wear rates" (not "in all cases"). This paper also talks in depth about brake fade.

There are a few other papers out there, but I have not read any more relevant that I can remember.

-td

[Benjamin Choi]

if it ain't broke, don't mess with it.

porsche brakes --> best factory setups

[Michael-Dallas]

I suggest folks read this themselves: it is HIGHLY biased towards cross-drilling. AND it does not account for slotted or dimpled rotors or other engineered solid rotors. ONY completely solid ones (see the picture on page 24) and p.23 where they admit they didn't even look at slotted or dimpled rotors). It is unclear what types of venting/vaning the solid rotors they used have - if any!

The article is about the performance effects of cross-drilling rotors and uses solid rotors as a baseline for comparison, that is why slotted or dimpled rotors are not included. If the paper was titled, "The Performance Effects of Rotor Design" then it would make plenty of sense to compare cross-drilling, slotted, dimpled, solid, etc.

Because of these fundamental issues, it is easy to find snippits favorable to cross-drilled rotors in the article - but only as they are compared to generic solid rotors. Again, ONLY completely solid rotors, and not race rotors with slots / dimples / vanes / vents, etc. [Note that there is plenty of discussion about the vaned design of the x-drilled - but almost no discussion on the type or design of the solid rotor. Clearly a Brembo (or other) solid rotor will operate better than less "engineered" models.] Despite the fact that they used junk solid rotors, there were still a number of points favorable to the non-crossdrilled rotors they tested!

Page 3 states that brake system 3b (solid rotors) is identical to 3a (cross-drilled rotors), except 3b rotors were smaller in diameter. Both systems were tested on the same "high peformance sports car." In addition, it states under "Rotor Cooling on Brake System 1":

"of otherwise identical design" -- I think that establishes what kind of solid rotors were used when comparing against cross-drilled rotors in brake system 1.

Also, keep in mind that their test does not accurately represent real world use. For example, the tests were not dramatically affected by pad build up in the holes. This will severely change the results, since the ENTIRE premise of the article is that the holes help. In fact - they indicate that OVER 90% of the hole will clog under use! [brake system 1, full. Brake system 2, 90%.] They also state that this can have really bad results. [This also illustrates that new pad technology does NOT need the holes for venting gas.]

While I don't doubt this point, but is there anybody out there that daily drives their Porsche and has encountered 90% pad build up in the holes? And are the holes for venting gas or cleaning the pad face (like slotted rotors)?

The point I am trying to make is, Porsche selected cross-drilled rotors for specific reason(s). Was it for marketing? Perhaps, but I would be more inclined to believe it if Kia or Hyundai slapped cross-drilled rotors on their mid-sized luxury sedans. But Porsche, Ferrari, Lamborghini, Corvette, GT-R, etc. all have cross drilled rotors, oversized cross-drilled rotors at that. I find it suspect that Porsche would spend years and years on suspension R&D, chassis R&D, engine R&D, tire R&D, fluid R&D only to slap cross-drilled rotors as a complete marketing / bling gimmick.

Are cross-drilled rotors adequate for a pro-am racer running an enduro? Probably not. Are they adequate on an auto that has power mods, track rubber, and/or suspension mods? Perhaps, depending on your driving experience. Are they adequate for a relatively stock car (just pads/fluid) at the track? IMO, absolutely.

///Michael

[torontoworker]

Actually - the term 'cross drilled' applies to cheap after market rotor companies that tried to reinvent the rotor on the cheap. They saw what the OEM spec's were and fired up the drill presses as it is cheaper for them but not for you in the long run.

1. Porsche OEM rotors are all CAST holes at the time of manufacture and are not 'drilled' after the fact.

2. The holes are there to clean the pad's of debris (wiping motion) more then for cooling, however there is a side benifit to the holes for cooling as the center slots on the rotor and their unidirectional (check your part numbers! Plus the R or L stamped on them) internal pathways do connect with the holes in the rotors.

Edited October 17, 2009 by torontoworker