I posted this in the LS1 tech section and I am kind of hoping some guys here can give me some more insight. 95% of this info came from one guy and I would like some more "in depth" opinions about this stuff.

There has been a growing "slotted vs cross drilled vs flat vs do it yourself" kind of thing going on and I would just like to start this post for an open ended kind of discussion regarding air flow, cooling, and practical uses.

Thanks guys-


Mark,
Not to nitpick, but i would like to throw in my two cents here.
I work at TRW automotive in their Livonia facility, which is their Braking systems research and development facility.

First off, I would like to say I am a co -op student there and not a full time engineer till i get out of school (assuming we both want me to work there at that time). WIth that said, most of this information is second hand and comes fom the senior engineers. Most of it actually come from my former supervisor who was a big autocross guy and former F-body owner.

Slots and cross drills are not for cooling and provide a very minimal amount of cooling. the majority of the cooling comes from the vents and the size of the rotor and its thickness.
The vents can create some pretty nice air flow inside and around the rotor.

The slots and holes do not have a significant amound or air flow around them. Althought this can be debated since real world air flow in that region is a stab in the dark on a good day. It is pretty well agreed upon that those slots and hole do very little for cooling though. The air in there is almost stationary when compared to the vents and the air along side the rotor (particularly outboard braking plate). The air is flowing from left to right (when looking at the rotor head on- looking at the wheel stud holes). Very little air is flowing from the inboard to ourboard rotor plates or vice versa. The air inside the vent holes is pretty stagnant in there compared to the air along the outboard rotor and air in the vents. The vents can work because they utilize the air flowing from left to right, not "into" the rotor. They are like little fans.

Plus the amount of surface area has probobly trippled or quadrroopled with these vents. here is now two more surfaces in the middle (effectivly doubling surface area right there) and the additional surface area of the 4 surfaces of the vent.

If i had to guess, I bet that there is VERY little air flow inside the wheel well t begin with- and particualry under our cars relative to most other cars. The low stance and air dam really should do a good job of making sure air doesn't go crazy under there.

As far as breaking power goes, they will reduce your breaking power since a good percentage of your friction is lost. i'd guess around 10% of your pad is no longer creating any friction.

These slots and holes are for releasing gasses that build up under high heat and pressure of panic stops (or aggresive driving). With the pads used in todays vehicles, there are EXTREMLY little gasses prodeced, if any at all. If there is any, its prety much negligable.

As far as drilling your own (did i read that somewhere?), I am pretty sure.

a. slotted/cross drilled rotors are thicker/stronger than OEM

b. it has to be PEFRECTLY balanced or life will be ****ty

c. It is extremely hard to drill evenely, effectively and safely.
You have to drill correctly (dont crack the rotor!), symetrically (dont throw it off balance) and you CANT HIT ANY OF THE VENTS!. doing the last two tegether will prove to be a challenge since most rotors have a prime number (hence odd) number of vents. This is done purposely do make as FEW LINES of symetry as possible. Less lines of symetry = less noise for a mutitude of reasons over my head, I didn't really get it when my boss explained it to me. So drilling symeticrially and not hitting nonsymetrical vents might prove to be a mathematical nightmare!

In this long winded responce, i kind hoped to get at this. Slotted and cross drilled are realy only good for appearance mods. If anything they will probobly warp and/or crack faster with all things being equal (which they are not for obvious reasons)

Personally, I am going to try some stuff out and see what happens. Although it probobly wont be as cost effective as the LS1 or C5 brake upgrade- I am drawn to doing it. I guess my natural curriousity is doing it to me. I am going to attempt to make two ducts (one for each front rotor) to cool the inboard rotor. Kind of like "ram air" to the rotors if you will. I will do some measurements to see how well it stops- although i cant really guarntee accuraccy. I am also going to swap in the most exensive/best brake fluid i can find and see what that does- maybe even find some crazy way of cooling it Then i'll probobly just do the LS1 brake upgrade and get some Hawk Pads. Thats probobly the best bang for the buck (well, the majority of you guys already have the "LS1 brake upgrade."

With the above said, a set of high quality "solid" vented (99% are now a days) rotors would probobly suit you best for your application. Who makes them or what they cost is beyond me. I was just doing some late night LS1 reading tonight and stumbled across this. I would't worry too much though about the car, warped rotors are pretty common on LS1's. Hell a drive through a puddle/car wash after a long drive can do it.

Mark please dont (and I hope you didn't) take this as an attack on you or your buisness, merchandise or expertise. I was really hesitant to type all of this seeing how you are a new supporter of this website. I am really all for supporters of this site and encourage/suggest to member to buy from here whenever possible.

here is another thread about rotors that I wrote a few days ago, cant remember if its relavent or not... i think its mainly just production methods.

http://web.camaross.com/forums/showt...r&pagenumber=2

Anyway, its amost midnight, i'm tired and its raining so I think I am going for a jog. I've been staring at rotor blueprints and talking about them too much. I think its bordering unhealthy at this point
please pardon my terrible spelling and -i'm sure- numerious typos.

 

I agree with what he says.

For a street, stip, or even a road racer/auto-x that isn't spoonsored, I would go with slotted rotors. Why?

Cross drilling rotors, is not for extra cooling. Most racing teams cross drilled the rotors to reduce unsprung weight. Over time, little stress fractures form around the holes in the rotors. Now since racing teams were only using the same rotors for a few races, they could replace the rotors and not be worried about it. For the above mentioned application, we are normaly trying to get 50+ thousand miles outta the same set of rotors.

Now yes, the heat and abuse on street brakes is no where near what racing, of any kind is, its really up to the buyer. \

Slotted rotors are in my favor because they reduce a little weight, with out the cracking, and help pad gases escape more easily. Also they increase the pads bite, and the slots will 'clean' off the pad surface and allow it to bite into the rotor much harder, increasing braking force.

Vanes are the part of the rotor that does tha coolin.

I would never suggest cross drilling a rotor yourself, unless you REALLY know what you are doing.

Now that it is the age of tech, and all kinds of new developments are being done each minute, cross drilling may be the way of teh future for all cars. I have talked to some Brembo people, and they are supposedly testing different heat treatments, cryo treatments and nitriding to allow cross drilled rotors not to crack. So not all hope is lost!!!!

thats my 47 cents

Hunter

 

How much weight is reduced if any at all? Correct me if i am wrong, but they would actually be HEAVIER. Slotted and cross drilled rotors must be thicker to avoid cracking if i am not mistaken.

I always thought the purpose of drilling rotors was to release the gas build up in old vehicles and this was just another example of something that cant be carried over from older cars (like throttle body spacers)

 

Brembo casts the holes in many of their rotors, which greatly decreases the chance of cracking. They also pay a great deal of attention to airflow management within the rotor - ever see a cutaway of a 911 rotor? It's damn impressive. Hunter hit the reason for "drilling" on the head, though - it's for weight reduction (and fashion, and let's not forget good ol' tradition).

My understanding of slots is that they're primarly useful when running organic pads that tend to "outgas" when heated, so we're not talking about something that's really relevant to modern braking systems (unless you like to run the best pads that $7 will buy at NAPA ). There may some other reason for slotting that I'm not considering (pad cleaning, water dispersion, etc.); it's notable that while they're some slotted rotors on high-end race cars, they're by no means present on every single braking system so even the "pros" disagree on this subject.

 

If someone can get my the specs on a cross drilled an LS1/LT1 rotor (diamter, hat height, brake plate widths, number of drillings and size of drillings) I can use the softwear here at work to see the inertial differanes.

I also need stock specs to compare

 

100 holes 1/4 inch diameter and 3/8 inch long represent about one-half pound of cast iron.

 

how much thicker is the rotor though? even 1/16inch on each plate would more than compensate, no?

I could see a "strait line" rotor that isn't strong and is built to be light (ie aluminuim rotors on prowler ) but to have equal strengeth... or at least acceptable for that matter???

 

On a C5 Vette front rotor, 1/16 inch added to each friction surface would add over 2-1/2 pounds.

 

This answer begs the question-
Is a cross drilled or slotted rotor thicker than a its blank counterpart?

I think I'm going to go to the local casting place and get some aluminum rotors for $150 a pop. THAT is some serious weight reduction!

 

Adding thickness to a drilled rotor only makes the cracking problem worse, as you typically increase the temperature difference (thermal gradient) between the inner and outer surface of the rotor "cheek".

Of course, this isn't a problem with unvented rotors, which is why bikes get away with properly-manufactured drilled rotors.

 

I don't think "treyZ28" ment aluminum rotors. There are aluminum "hats" and other components but not rotors. If you want to cut rotor weight you have to go to carbon or ceramic rotors.

 

Eric, how would a thicker plate create more heat? Discussing a test or two done here and some research, thicker plates can hold more heat and are more resistant to cracking.

also would it be that much colder by the holes seeing how the holes really dont cool much of anything

 

A rotor with more mass will be able to dispell heat easier, therefore the rotor itself will not heat up as much. That is the reason these guys are running 13-15" rotors, because a bigger rotor is a bigger heatsink.

Otherwise we'd all be running 8" rotors wouldn't we.

 

my mistake i worded it wrong. obviously a larger rotor will hold more heat enegry-

but would it be any hotter than a smaller rotor?

either way 1/2 (mass car) (change in velocity)^2 engery needs to go into the rotors (or close to for theoreticaly purposes)

wouldn't a heavier rotor be cooler?

i'm guessing more energry, less hot in a larger rotor??

 

A solid rotor may not tend to crack, but better believe they have warpage problems up the yin yang.

No, the smaller rotor would retain more heat because it can't hold it (and then dump it) like a larger rotor will. A larger rotor has more surface area to the atmosphere, and more flat out mass. Think of the suns heat energy here on the small planet earth, obviously the sun will take the abuse better than we can.

Same reason the better heat sinks are LARGER. You dont put a 486 heat sink on a Pentium IV.