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Slotted and Drilled rotors

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Old 04-17-2009, 11:54 AM
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AllStock
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Default Slotted and Drilled rotors

Ok I'm trying to upgrade my rotors to Slooted and/or drilled rotors.. I already have Brembo brake kit since its a GT trim.

I'm just trying to upgrade my rotors and keeping the pads since they are still in good condition.

what kind of rotors are good? and where should I buy them?
Old 04-18-2009, 01:19 PM
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SpeedRcr
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dba
Old 04-18-2009, 02:47 PM
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300zx1985
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If you are going for performance dont even both with drilled and slotted
Old 04-18-2009, 03:49 PM
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chrisjersey06
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I believe drilled ones have the possibility of cracking under intense heat, but don't quote me. I chose just slotted for mine.
Old 04-18-2009, 04:18 PM
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specialized5223
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cross drilled for weight reduction and slotted for cooling. and chris is right, they can break under extreme heat from heavy track use
Old 04-19-2009, 07:54 PM
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AllStock
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well, where can I get them? can anyone direct me to a website?
Old 04-20-2009, 09:24 PM
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sloloco
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I believe drilled ones have the possibility of cracking under intense heat, but don't quote me. I chose just slotted for mine.
That's spot on, I have seen it first hand at Buttonwillow. Upon severe heat cycling and braking you may end up with hairline cracks between drill holes. Stick with slotted or slotted and dimpled.
Old 04-21-2009, 04:47 AM
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DBA has 2 types

the 4000's are slotted/drilled, and offered in front/rear fitments. The slotted/drilled ones have a gold rotor hat - you can always paint or powdercoat it to whatever color you want.

http://www.z1auto.com/prodmore.asp?m...ng&prodid=3695

They also make a 2 piece rotor, called the 5000 series. These come standard with black hats, but also can be purchased with gold, red, or blue hats as an option. The 5000's are only offered for front, not rear

http://www.z1auto.com/prodmore.asp?m...ng&prodid=2312

let us know if you need a set
Old 04-21-2009, 12:53 PM
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StopTech
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If you have the OE Brembo brakes, you may want to consider the StopTech 2pc rotors. They will fit within your calipers, and drop 2.5lbs per rotor. The lighter rotors will let you put down more power to the ground while increasing the heat capacity of your brakes.
Old 04-21-2009, 12:59 PM
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Originally Posted by StopTech
If you have the OE Brembo brakes, you may want to consider the StopTech 2pc rotors. They will fit within your calipers, and drop 2.5lbs per rotor. The lighter rotors will let you put down more power to the ground while increasing the heat capacity of your brakes.
Can you direct me to a direct website where I can order them?
Old 04-21-2009, 01:05 PM
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we have those too

slotted or drilled, but they don't offer both
Old 04-27-2009, 09:14 PM
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If you plan to track your car at all I wouldn't recommend drilled rotors. I'd go with blanks or slotted. I also wouldn't recommend DBA's as I had a brand new pair (drilled and slotted) crack down to the hats on my z32 a few years ago after a single day of track use. Their quality might be better now, but what I bought a 4-5 years ago was absolute garbage. They might be fine for street use though. Stoptech or brembos would be a safer bet.
Old 04-28-2009, 03:24 PM
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Get Powerslot rotors.

www.powerslot.com

www.tirerack.com
Old 04-28-2009, 09:08 PM
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I have the OEM brembos as well and need new front rotors.

I'm going with the one-piece slotted stoptech rotors. Powerslot or whatever else should be fine and two-piece even better, but honestly I'd get the least expensive one-piece rotors for myself.
Old 04-29-2009, 07:16 AM
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Yeah. I'm not trying to spend thousands of dollars for rotors since I'm not planning on track my car at all. This is my DD and I just want a least expensive rotors that's better than OEM rotors.
Old 04-29-2009, 10:15 AM
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I posted some information on Driver...see below (a lot of reading, but well worth the time). I went with Stoptech slotted fronts and blank rears for my Akebono BBK. I do track my car and I did not want the stress risers.....errrr cross drilled rotors. Interesting that Porsche does not actually drill their rotors, they are cast in during the manufacturing process. If I were you, the Stoptech Stage 2 kit would be an all around daily driving, occasional track excellent fit. Go to the marketplace and search Vendors for brakes.

===========
First, lets get some physics. Tell me how a heatsink with less mass will cool better? You do realize that a brake rotor acts as a large heatsink to transfer heat from the brake pads to the rotor. The heat generated from pads has to go somewhere and so it transfers to the rotor and caliper.

Porsche claims: "Discs are cross-drilled to enhance braking in the wet. The brakes respond faster because the water vapour pressure that builds up during braking can be released more easily."

They have said nothing about enhancing normal braking circumstances and the larger diameter rotors probably make up for the lack of material present in a smaller cross drilled rotor.

From Wilwood's website:
QUOTE
Q: Why are some rotors drilled or slotted?
A: Rotors are drilled to reduce rotating weight, an issue near and dear to racers searching for ways to minimize unsprung weight. Drilling diminishes a rotor's durability and cooling capacity.

Slots or grooves in rotor faces are partly a carryover from the days of asbestos pads. Asbestos and other organic pads were prone to "glazing" and the slots tended to help "scrape or de-glaze" them. Drilling and slotting rotors has become popular in street applications for their pure aesthetic value. Wilwood has a large selection of drilled and slotted rotors for a wide range of applications.

As for the porsche rotors, a few notes from a forum I frequent:
QUOTE

1) The holes are cast in giving a dense boundary layer-type crystalline grain structure around the hole at the microscopic level as opposed to drilling which cuts holes in the existing grain pattern leaving open endgrains, etc, just begging for cracks.

2) The holes are only 1/2 the diameter of the holes in most drilled rotors. This reduces the stress concentration factor due to hole interaction which is a function (not linear) of hole diameters and the distance between them.

3) Since the holes are only 1/2 as big they remove only 1/4 as much surface area and mass from the rotor faces as a larger hole. This does a couple of things:

It increases effective pad area compared with larger holes. The larger the pad area the cooler they will run, all else being equal. If the same amount of heat is generated over a larger surface area it will result in a lower temperature for both surfaces.

It increases the mass the rotor has to absorb heat with. If the same amount of heat is put into a rotor with a larger mass, it will result in a lower temperature.

3) The holes are placed along the vanes, actually cutting into them giving the vane a "half moon" cut along its width. You can see that here:

This does a couple of things:

First, it greatly increases the surface area of the vanes which allows the entire rotors to run cooler which helps prevent cracks by itself.

Second, it effectively stops cracking on that side of the hole which makes it very difficult to get "hole to hole" cracks that go all the way through the face rotor (you'll get tiny surface "spider cracks" on any rotor, blank included if you look hard enough).

That's why Porsche rotors are the only "crossdrilled" rotors I would ever consider putting on my car.

BTW, many of the above features are not present in older Porsche brakes. The above is for "Big Reds" and newer.

This is quite different from the standard drilled rotors you get from brembo/kvr/powerslot/"insert random ricer parts brand name here" brake rotors.

Further proof of the uselessness of cross drilled rotors are found here:

Those Poor Rotors

QUOTE
Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the 40’s and 50’s, not a whole lot. Rotors were first ‘drilled’ because early brake pad materials gave off gasses when heated to racing temperatures – a process known as ‘gassing out’. These gasses then formed a thin layer between the brake pad face and the rotor, acting as a lubricant and effectively lowering the coefficient of friction. The holes were implemented to give the gasses ‘somewhere to go’. It was an effective solution, but today’s friction materials do not exhibit the same gassing out phenomenon as the early pads.

For this reason, the holes have carried over more as a design feature than a performance feature. Contrary to popular belief they don’t lower temperatures (in fact, by removing weight from the rotor, the temperatures can actually increase a little), they create stress risers allowing the rotor to crack sooner, and make a mess of brake pads – sort of like a cheese grater rubbing against them at every stop. (Want more evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it.)

The one glaring exception here is in the rare situation where the rotors are so oversized (look at any performance motorcycle or lighter formula car) that the rotors are drilled like Swiss cheese. While the issues of stress risers and brake pad wear are still present, drilling is used to reduce the mass of the parts in spite of these concerns. Remember – nothing comes for free. If these teams switched to non-drilled rotors, they would see lower operating temperatures and longer brake pad life – at the expense of higher weight. It’s all about trade-offs.


From Stoptech:

QUOTE
Which is better, slotted or drilled rotors?

StopTech provides rotors slotted, drilled or plain. For most performance applications slotted is the preferred choice. Slotting helps wipe away debris from between the pad and rotor as well as increasing the "bite" characteristics of the pad. A drilled rotor provides the same type of benefit, but is more susceptible to cracking under severe usage. Many customers prefer the look of a drilled rotor and for street and occasional light duty track use they will work fine. For more severe applications, we recommend slotted rotors.

That almost sounds like an excuse to use cross drilled rotors, and for your street car which probably is never driven on the track, the drilled rotors are fine, but as Stoptech states, they will crack and are not good for severe applications.

From Baer:

QUOTE
"What are the benefits to Crossdrilling, Slotting, and Zinc-Washing my rotors?

In years past, crossdrilling and/or Slotting the rotor for racing purposes was beneficial by providing a way to expel the gasses created when the bonding agents employed to manufacture the pads...However, with today’s race pad technology, ‘outgassing’ is no longer much of a concern...Slotted surfaces are what Baer recommends for track only use. Slotted only rotors are offered as an option for any of Baer’s offerings."
Old 04-29-2009, 10:16 AM
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twin001
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QUOTE

Here is how it works. The friction between the pad and rotor is what causes you to stop. This friction converts your forward energy into heat (remember Einstein: Energy is neither created nor destroyed, it is converted). Now that heat is a bad thing. Yes it is bad for the rotors but it is a lot worse for the pads. A warped rotor will still stop the car - it will just feel like ****. Overheated pads however WILL NOT stop the car. It is here where the rotors secondary responsibility comes in. Its job now is to DISSIPATE the heat away from the pads and DISPERSE it through itself. Notice that DISSIPATE and DISPERSE are interchangeable? Once the heat is removed from the pad/surface area it is then removed. Notice where the removal falls on the list of duties? That's right - number 3. Here is the list again. Memorize it because I will be using it a lot in this post:

#1 Maintains a coefficient of friction with the pad to slow the forward inertia of the vehicle

#2 DISSIPATE the heat

#3 REMOVE the heat from the brake system

Let's look more in-depth at each step now shall we? No? Too bad assclown we are doing it anyway.

#1 Maintains a coefficient of friction with the pad to slow the forward inertia of the vehicle:

This one is pretty simple and self-explanatory. The rotor's surface is where the pads contact and generate friction to slow the vehicle down. Since it is this friction that causes the conversion of forward acceleration into deceleration (negative acceleration if you want) you ideally want as much as possible right? The more friction you have the better your stopping will be. This is reason #1 why BIGGER brakes are the best way to improve a vehicle's stopping ability. More surface area on the pad and the rotor = more friction = better stopping. Does that make sense Ace? Good. Let's move on.

#2 DISSIPATE The Heat:

Let's assume for a second that the vehicle in question is running with Hawk Blue pads on it. The brand doesn't really matter but that is what I am using as my example. They have an operating range of 400 degrees to 1100 degrees. Once they exceed that 1100 degree mark they fade from overheating. The pad material gets too soft to work effectively - glazing occurs. This means that a layer of crude glass forms on the surface of the pad. As we all know glass is very smooth and very hard. It doesn't have a very high coefficient of friction. This is bad - especially when I am coming down the back straight at VIR at 125MPH. Lucky for us the rotor has a job to do here as well. The rotor, by way of thermal tranfer DISSIPATES the heat throughout itself. This DISSIPATION lessens the amount of heat at the contact area because it is diluted throughout the whole rotor. The bigger the rotor the better here as well. The more metal it has the more metal the heat can be diluted into. Make sense? This isn't rocket science here d00d.

#3 REMOVE the heat from the brake system:

Now comes your favorite part of the process. This is what you thought DISSIPATION was. It is ok. I will allow you to be wrong. This is the step where the rotor takes the heat it DISSIPATED from the pads and gets rid of it for good. How does it do this? By radiating it to the surface - either the faces or inside the veins. It is here where cool air interacts with the hot metal to cool it off and remove the heat. Once again there is a reoccuring theme of "the bigger the better" here. The bigger the rotor, the more surface area it will have which means more contact with the cooling air surrounding it. Got it? Good.

Now let's look at why cross-drilling is a bad idea.

First - as we have already established, cross-drilling was never done to aid in cooling. Its purpose was to remove the worn away pad material so that the surfaces remained clean. As we all know this doesn't have much of a purpose nowadays.

Next - In terms of cooling: Yes - x-drilling does create more areas for air to go through but remember - this is step 3 on the list of tasks. Let's look at how this affects steps 1 and 2. The drilling of the rotor removes material from the unit. This removal means less surface area for generating surface friction as well as less material to accept the DISSIPATED heat that was generated by the friction. Now because of this I want to optimize step one and 2 since those are the immediate needs. If it takes longer for the rotor to get rid of the heat it is ok. You will have a straight at some point where you can rest the brakes and let your cooling ducts do their job. My PRIMARY concern is making sure that my car slows down at the end of the straight. This means that the rotor needs to have as much surface as possible to generate as much friction as possible and it needs to DISSIPATE the resulting heat AWAY from the pads as quick as possible so they continue to work. In both cases x-drilling does nothing to help the cause.

Now let's talk about strength - and how x-drilled rotors lack it. This one is simple. Explain again just how drilling away material/structure from a CAST product DOES NOT weaken it? Since you are obviously a man of great knowledge and experience surely you have seen what can happen to a x-drilled rotor on track right? Yes it can happen to a non-drilled rotor as well but the odds are in your favor when pimpin' bling-bling drilled y0! Since you are also an expert on thermodynamics why not explain to the group what happens to a cast iron molecule when it is overheated. I will give you a little hint - the covalence bonds weaken. These bonds are what hold the molecules together boys and girls. You do the math - it adds up to fractures.

So why don't race teams use them if they are so much better? Consistency? Hmmmm . . . no. I am gonna go with the real reason her chodeboy. It is because of several factors actually. They are as follows but in no particular order:

- Less usable surface area for generating friction

- Less material to DISSIPATE the heat away from the pads

- Less reliable and they are a safety risk because of fatigue and stress resulting from the reduced material

And what are the benefits? Removal of particulate matter and enhanced heat removal. I gotta tell ya - it is a tough choice but I think I am going to stick with the safe, reliable, effective-for-my-stopping needs solution
Old 04-30-2009, 09:16 PM
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guitman32
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Search around for some blank Centric rotors (get the premium version). Centric supplies StopTech with their rotors. Best value and performance for your money.
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