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Old 05-29-2014, 10:40 PM   #1
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Blank vs Cross-drilled vs Slotted brake rotors

Are the holes and slots really worth it/ make that noticeable difference? I've always just gone with blanks due to my previous knowledge and understanding about break rotors (decent write-upWHY Blank rotors are better than cross drilled and/or slotted - Honda-Tech) but I've seen members with cross-drilled/slotted rotors. It's come time for me to change my brakes and I've already orfered stainless steel lines and some Hawk pads but still have not ordered any rotors..

Any and all opinions wanted.... .
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Old 05-30-2014, 02:49 AM   #2
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When I work the hot grid at Road America for all the big Porsche events and sprint races, I've never seen a single car without either slotted or cross-drilled rotors.
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Old 05-30-2014, 05:27 AM   #3
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Blank rotors are completely adequate for street use, and they last longer. Drilled rotors tend to develop cracks radiating out from the holes. Don't know about slotted.

I think a lot of the cars you see on the street have drilled/slotted rotors because they "look cool" and their deployment is justified by vague claims of "better performance".
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Old 05-30-2014, 05:38 AM   #4
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Dimpled rotors offer the advantage of cross-drilled while maintaining the structural rigidity of the rotors.

Slotted is just as effective but they shave your pad materials quicker than blank.

http://www.apexperformance.net/prod-2519.htm

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Old 05-30-2014, 09:22 AM   #5
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I prefer blank Zimmerman rotors but dimpled or slotted are probably fine. I see no performance advantage to cross-drilled but they do look cool.
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Old 05-30-2014, 04:46 PM   #6
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I have driven blank, slotted, and drilled rotors on the track and I could notice a difference. I prefer the drilled rotors without a doubt. Does it really help me shave time off? Unknown; but I definitely like the feel of the drilled rotors. YMMV.

Drilled rotors will definitely crack out over time and the harder you use the brakes, the sooner this will happen. I replace my rotors with every pad change so the cracking isn't an issue for me but it is slightly more costly to do it this way (but worth it to me).

http://986forum.com/forums/general-discussions/43520-i-think-its-time-change-rotors.html
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Old 05-30-2014, 09:29 PM   #7
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Thanks for the input guys. I think at this point I'll start looking into some slotted rotors.
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Old 05-31-2014, 03:18 AM   #8
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I may be way off on this but are all drilled rotors actually drilled ? What I mean is I thought I read somewhere on the net or car forums that some " drilled " rotors actually have the holes cast in when the rotors are being made. Supposedly the cast in holes do not exhibit the hairline cracking like rotors where the holes are machined after casting the rotors. Anyone else heard/seen that ?
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Old 05-31-2014, 04:49 AM   #9
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Originally Posted by rfuerst911sc View Post
I may be way off on this but are all drilled rotors actually drilled ? What I mean is I thought I read somewhere on the net or car forums that some " drilled " rotors actually have the holes cast in when the rotors are being made. Supposedly the cast in holes do not exhibit the hairline cracking like rotors where the holes are machined after casting the rotors. Anyone else heard/seen that ?
You are correct; rotors with the holes cast in (such as Porsche OEM rotors) are much less prone to cracking than aftermarket rotors with holes drilled in.
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Old 05-31-2014, 05:10 AM   #10
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I had the pleasure of being at an event with a manufacturers rep. Casting with the hole does 2 things. It reduces machining time, and tool wear, while increasing the edge strength that improves resistance to edge cracking.

The hole idea of cross drilling is to improve heat transfer out of the disc pad and rotor. Heat radiates until it hits an edge and builds up there. The internal fin force air out the hole improving surface cooling. With out the cross drilled holes all you do is cool the core of the rotor. With the cross drilled hole you cool the core and the friction surface. If you've ever watched the thermal imaging of a solid rotor versus a Cross drilled rotor it is impressive how fast the edges of the holes get hot and how fast they cool back down. While the solid one just linger hot and gradually increase overall temperature with repeated braking. I saw a side by side thermal test for 3 minutes. Braking for 5 second cooling for 15 seconds designed to simulate track conditions. the solid rotor was over 150 degrees hotter at the end of 3 minutes with a 22% loose of braking force.

My opinion would be, If the car is a daily drive then use solid rotors. If you track the car at all use drilled or drilled and slotted rotors.
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Old 05-31-2014, 05:21 AM   #11
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He also had some impressive test to fail video of, Solid rotors, forged then drilled, cast then drilled, and cast with the holes treated then drilled. Guess which one didn't have a catastrophic failure.
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Old 05-31-2014, 05:39 AM   #12
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Send your new rotors out for cryogenic treatment. <$200.
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Old 05-31-2014, 06:31 AM   #13
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I had the pleasure of being at an event with a manufacturers rep. Casting with the hole does 2 things. It reduces machining time, and tool wear, while increasing the edge strength that improves resistance to edge cracking.

The hole idea of cross drilling is to improve heat transfer out of the disc pad and rotor. Heat radiates until it hits an edge and builds up there. The internal fin force air out the hole improving surface cooling. With out the cross drilled holes all you do is cool the core of the rotor. With the cross drilled hole you cool the core and the friction surface. If you've ever watched the thermal imaging of a solid rotor versus a Cross drilled rotor it is impressive how fast the edges of the holes get hot and how fast they cool back down. While the solid one just linger hot and gradually increase overall temperature with repeated braking. I saw a side by side thermal test for 3 minutes. Braking for 5 second cooling for 15 seconds designed to simulate track conditions. the solid rotor was over 150 degrees hotter at the end of 3 minutes with a 22% loose of braking force.

My opinion would be, If the car is a daily drive then use solid rotors. If you track the car at all use drilled or drilled and slotted rotors.
While drilled (or cast hole) rotors do dissipate heat quicker, their true advantage is in gas control. Disc brake pads are held together by bonding resins which turn into gas vapor under the heat of hard braking, much the way water turns into steam under the same conditions. On a really fast moving race car, the gas generation (from resin or steam during wet sessions) can actually hold the pad off the rotor slightly during braking, reducing the overall braking effort. Holes, slots, or dimples give the gas a pathway to escape, dramatically improving pad contact and braking.

One of the most common comments you get from an owner experiencing drilled or slotted rotors for the first time is how much better the car seems to brake in the rain, when cooling is obviously not an issue.
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Old 05-31-2014, 06:34 AM   #14
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Send your new rotors out for cryogenic treatment. <$200.
You can also look for the newer "high carbon" front rotors, which are made from a different type of alloy with much harder properties. High carbon rotors can last nearly twice as long as conventional units.
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Old 05-31-2014, 01:23 PM   #15
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High carbon rotors can last nearly twice as long as conventional units.
But won't it be at the expense of an increased pad wear rate?
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Old 05-31-2014, 01:27 PM   #16
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Last summer I replaced all 4 rotors and while they were under the min thickness limit, I could not find any evidence of cracking. Porsche knows brakes.
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Old 05-31-2014, 02:41 PM   #17
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But won't it be at the expense of an increased pad wear rate?
Not really, the rotors are not more aggressive in any way, just harder.
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Old 06-01-2014, 07:07 AM   #18
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Hi all, long time since I've been here. One thing to consider with street driving that seems
to never show up is a solid rotor could in some cases get a layer of water under the pad
and prevent you from stopping. The slots or holes wipe away the layer of water under the pad
and clean it. This happened to me once driving through a puddle very slow and then shortly
after not being able to stop. Never make that mistake again.
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Old 06-01-2014, 07:15 AM   #19
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I did a super cheap package off of ebay with the slotted, drilled, and cermic pads all for just over $200. They have been doing great for the past few thousand miles. No complaints.
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Old 06-01-2014, 11:17 PM   #20
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Unless you are tracking the car or autoxing really hard, the type of rotors for the streets do not make that much difference imo. The pad material is most important. Hawks are good pads to the OP.

Like another poster said, for the rain, I always "pre-bed or pre-brake" a couple of seconds sooner than I normally would to wipe the layer of water off of the rotor/pads. Never had any issues with hard rain stopping.
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