[Lord_Galva]

Hey guys. I've been surfing around and I wanna know 968 racer's opinions on this.

What is better for the track? Cross drill, slotted, or smooth?

(Brake Disks) [img]style_emoticons/<#EMO_DIR#>/tongue.gif[/img]

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[flash]

way too many factors involved for an easy call on that - define the parameters of the car, the setup, the type of tracks, etc

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[Lord_Galva]

Its on cars in general but I wanted people with "real braking experiance" ie track driving.

One of the latest forums I visited stated that "Only people who don't race use cross drilled, when I see a Porsche GT3 with cross drilled I think daily driver."

I am trying to prove him and others wrong with some evidence and proof. Or perhaps I will be enlightened. [img]style_emoticons/<#EMO_DIR#>/blink.gif[/img]

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[MC968CS]

Good question. I track and brake my 968CS with MO30 set up, including cross drilled rotors, pretty hard, and am about to give up on them - I am on my second set recently and they just crack all the time around the drill holes, and are OEM. Going to try the 928 non drilled type next aling with a cooling kit (paragon). My race mechanic, who runs everything from cup cars down, agrees that is the way to go too.

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[flash]

i always ran crossdrilled rotors - my buddy didn't - same car - some days he'd beat me - some days i'd beat him - it wasn't the brakes

most higher end race cars i see are drilled and/or slotted, and usually fully floating - production class stuff has a higher frequency of solid rotors generally because they are heavier

again though, this depends a lot on the setup of the car (different classifications have different limitations), the kind of track, etc - some cars are better off solid - some are better drilled - some slotted - some both

it isn't all one or all the other

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[josephsc]

I was talking to a guy with a Corvette Z06 at a track day, and for him, he said he wasn't having any cracking issues with cross-drilled. But then, that was because he was replacing brake rotors every track day!

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[Lord_Galva]

Hmmmm.

Good input.

I have been rooting around Porsche's website and noticed that nearly all of their race cars have either slotted or smooth brake discs.

For example the new RS has carbon-fiber disks which are smooth.
http://www.porsche.com/usa/eventsandracing...logyandconcept/

And the new 997 RSR has slotted brakes. (which look really cool btw)
http://www.porsche.com/usa/eventsandracing...logyandconcept/

It seems the consensus is smooth/slotted racing and slotted for concours/showing off. [img]style_emoticons/<#EMO_DIR#>/tongue.gif[/img]

This is actually good price wise too. For example I was looking up prices for a set of 350Z brake disks, and a set of OEM's were equivilant to ONE cross-drilled from EBC. OUCH!

Now finding slotted disks for a 968 is another problem. [img]style_emoticons/<#EMO_DIR#>/sad.gif[/img]

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[Torbjorn968]

<!--quoteo(post=76102:date=Jul 25 2009, 04:17 PM:name=flash)-->QUOTE (flash @ Jul 25 2009, 04:17 PM) <{POST_SNAPBACK}><!--quotec-->again though, this depends a lot on the setup of the car (different classifications have different limitations), the kind of track, etc - some cars are better off solid - some are better drilled - some slotted - some both

it isn't all one or all the other<!--QuoteEnd--><!--QuoteEEnd-->

If we limit it to your own car on typical US tracks where you would run the car what would you choose and why? And what variations of tracklayouts would make you consider the other alternative?

Cross drilled 993 RS rotors, cracking quite a bit but the opinion from many Porsche servicing places working with track day cars is that it isn't as bad as it looks.

Regarding slotting: this can often be done by a machine shop with the right skills, buy plain rotors and find the right workshop.

//TL

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[Lord_Galva]

<!--quoteo(post=76129:date=Jul 26 2009, 03:31 AM:name=Torbjorn968)-->QUOTE (Torbjorn968 @ Jul 26 2009, 03:31 AM) <{POST_SNAPBACK}><!--quotec-->Regarding slotting: this can often be done by a machine shop with the right skills, buy plain rotors and find the right workshop.

//TL<!--QuoteEnd--><!--QuoteEEnd-->

Good tip.

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[flash]

just as an example of how variant things are, on the west coast, i would be less concerned with slots, but on the east coast, where it might rain, i would definitely run slots

on this particular car, i have no braking issues, and run drilled rotors

over the 30 or so years of doing this, of all the cars i've worked on, i think i've seen a half dozed cracked drilled rotors that were still within spec - i've seen a lot more though that were solid and run down to beyond their minimum spec and/or with very worn pads

the single biggest factor in causing cracks is heat - the biggest mistake many people make is to run their brakes beyond their ability to dissipate the heat - the minimum wear specs in the shop manuals DOES NOT APPLY to race cars - you need to cut that tolerance at least in half

i am extremely careful when it comes to brakes, and take no chances - my practice is to change rotors whenever i got .020" of wear on them - i also change my pads when they have worn off 25% of their material - i do this to maintain the maximum amount of heat dissipating material - that amount of wear always happens before any cracks occur, so it is a non-issue for me

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[S_Cal968]

I'm surprized more haven't selected/use slotted. They essentially provide the advantages of c/drilled w/o the fatigue cracking.
I don't track my car, but I'm often heavy on the binders. I have slotted back and front and they've been great so far.

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[flash]

they can be a little noisy on a street car, and they tear up pads faster and make more dust - not the perfect scenario for the guy in the topsiders and polo shirt - but they do work well - the ones on the denali are crossdrilled AND slotted

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[S_Cal968]

Mine are just as quiet as the factory rotors and dust & wear are less due to a better quality pad...

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[flash]

mine make a slight ticking sound as they go over the slots, but you can only hear it at very low speed, radio off, and windows down - doesn't bug me, but might make somebody else nuts

i also have low dust, as i use porterfield pads, but with stock pads, there is an increase in dust as the edges of the pads hit the slots

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[S_Cal968]

The noise may be as a result of the slot configuration. My rotors have a straight slots, [vs. some that have multi diagonal or oval slots].

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[flash]

not sure about that - i've heard this on pretty much every slotted rotor car i've ever been in - but then, i tend to pay a lot of attention when it comes to noises and stuff - doesn't mean i won't run slots - i like slots and will run them too - it just means i'm aware of the issues

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[Clem]

Go slotted, as has been mentioned the drilled crack too quickly under stress.

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[rxter]

Just got diagonal slotted and drilled from flat stocks. They do growl when you get on them. This is not a Lexus so I am OK with a few noises. They stop well and with Bob's R4S pad selection the dust is definately lower than stock. And, oh, they look cool.

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[flash]

it's really hard to say "this or that" - even stoptech will tell you that both are good, but use and conditions are factors to consider - general statements like "drilled crack too quickly" are misleading - there are a lot of factors involved - were the holes cast in? if drilled, what pattern was used when they were drilled? did the holes get chamfered? how far down did you run the rotors? how far down did you run the pads? what kind of pads? how heavy is the car? how big are the rotors? how is the car driven?

i have yet to crack mine, and they have been on there for 5 years and about 25k miles - everybody will tell you i drive my car pretty hard too, so i would expect them to crack on my car if they were going to crack at all

that being said, i have done things to mitigate the issue and reduce the problem - i don't run the pads or rotors down, replacing them about halfway to the minimum spec - i also changed the bias valve, taking a lot of load off of the front rotors and putting it on the rear where it belongs

if you're going to drive them all the way to minimum spec, you might well crack them, especially on the track - if you change them out at half the minimum spec, the likelihood is greatly reduced - if you have a pad with a better heat coefficient, the likelihood is reduced - slots are less subject to those issues

all of the cracked drilled ones i've seen were worn down more than a millimeter and had very aggressive pads - most saw abusive track use - i have yet to see a cracked drilled rotor on a street car that has less than 1mm of wear on it

when i make my new rotors, they will likely be both drilled and slotted

however, as the question was for racing purposes, and we are talking about the 968, if you are staying with stock sizes, slotted is probably a better choice

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[Jim Child]

I use regular non drilled, non slotted rotors on my race car. I tried drilled rotors, and quickly developed severe cracking around the holes, so much so that I was not comfortable running them. Plus they cost more, and provided no benefit that I could detect.

I also tried a set of slotted rotors. One of those developed the most severe crack I've ever had - a giant crack from the hat all the way to the outside edge. Luckily I felt it in the pedal right away and got off the track. I can't directly attribute the crack to the slotting, but it left a bad taste in my mouth. Besides, I couldn't detect any benefit from the slotting and they cost more.

Since then I've come to the conclusion that for me plain old non-slotted, non-drilled factory 944 Turbo S rotors are the way to go. For those of you who have seen any of my videos you know that I don't have any problems making aggressive passes under heavy braking. I view braking as one of my car's primary strengths. Why should I pay more for rotors that don't last as long and provide no detectible benefit?

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