Lets Figure out if Cross drilling actually works

I know this has been discussed in the LT1 tech section but there everyone chimes in with an opinion where i want to know facts.

We know de-gasing is no longer an issue with brake pads.

So what it comes down to heat absorbtion and cooling.

A cross drilled rotor vs a non cross drilled rotor can not absorb as much heat as a due to it having less mass. But because its cross drilled will it beable to throw off more heat and let air cool it faster than the pad friction can generate heat on the rotor?

Surface area- Cross drilled rotors dont have as much surface area so wouldnt this cause them to be less effective in stopping? Less pad to rotor contact.

Maybe i should email Baer brakes this to see what they have to say. They use cross drilled and slotted rotors so it makes me believe that cross drilling is better.

Originally posted by ZDriver96

Maybe i should email Baer brakes this to see what they have to say. They use cross drilled and slotted rotors so it makes me believe that cross drilling is better.

They sell slottd/cross-drilled rotors because people think they look cool. The real racers use plain rotors.

At one point in time, Baer had a writeup on there website that indicated cross-drilling was purely cosmetic, and of no real value. I don't know if that statement is still there.

You also might want to go to Keith's web page at ws6.com. He has an extensive writeup on problems with cracking around the holes. He uses his car to run for extended periods at 150mph in the Silver State Classic, and had opted to use cryo treating, which seems to double the life of the rotors before he starts cracking them, but its still a very low number of miles. I have seen at least one other post on cracking problems with the cross-drilled rotors.... maybe Kelly Drown who runs Project TransAM and autcrosses..... or maybe someone else.

Have to agree with Injuneer and cASe above with respect to vented iron rotors. With motorcycle or bicycle thin solid rotors, there might be a case for x-drilling. A friend develops high end parts for off-road bicycles, and his 1/8 inch thick rotors are always drilled/milled.

The vanes are there in vented rotors to pump air from the center of the rotor to the outside edge to transfer heat from the iron to the air. In my mind, the x-holes disrupt and/or short circuit the air, as well as reduce the heat transfer area.

Winston Cup cars on short tracks and road courses have some of the most severe braking demands of any car. The must use iron discs which fit inside a 15 inch steel wheel to slow down a 3500 lb. vehicle as often as every 10 seconds (or less!) a thousand times in a 500 lap race. We've all seen the glowing discs on TV; you may have noticed that at times the glow never fully disappears even on the straight, so the disc isn't getting below 1000*F or so during green laps. Caution laps allow the discs to cool dramatically then they immediately go back to glowing.

My point is these folks do not cross drill.

Done correctly like casting in the holes probably prevents most cracking, but I don't think it's worth it. I hate it when the 'look" outweighs the "function" of a part.

Some expensive street cars use "drilled" rotors, Porsche are as-cast and not actually drilled.

Race cars do not use this feature, I think that says it all right there.

Thank you to all the pros :D

that fact that baer and some of the others used cross drilled were confusing me. I thought that it was worthless for performance. Now i know for sure.

Its all about the bling bling.

Surface area- Cross drilled rotors dont have as much surface area so wouldnt this cause them to be less effective in stopping? Less pad to rotor contact.

That wouldn't affect the stoopping ability of the car, the same force with less surface area just means more PSI on the available area, but that leads to more wear which is pretty commonly known with X drilled.
Also if the holes arent chamfered they're very likely to crack regardless of the metal/cryo treating/etc you use or do to it, alot of the bargain ones dont use that process.
I'll stick to slotted, they wear the pad a bit faster but keep it from getting glazed at high temps, good way to keep the surface clean.

I wouldn't use them period... not cast... not drilled. Porsche and Mercedes are using some ceramic composite brake material on their really high end cars... suppose to be much superior but mucho expensivo.
Best thing to do is to just use slotted. If you want the x-drilled look there are a few companies doing them with dimples and from a couple feet away... you can't tell the difference. To get rid of some unsprung weight, use a rotor with an aluminum hat.

-Mindgame

i am sure i can be proven worng but i will give it a shot, i thought that the drilled discs where mainly used in lemans gt car, i know that in cars such as the porsche gt2 air flows from the lower air dam and flows air threw the radiator then it is guided to the brakes, i would guess that the air flows through the drilled discs in this car to keep the discs cooler and prevent wear in long runs.

Drilling is for looks only.

We have had good luck with Slots in the rain on street cars ;)

Originally posted by number77
i am sure i can be proven worng but i will give it a shot, i thought that the drilled discs where mainly used in lemans gt car, i know that in cars such as the porsche gt2 air flows from the lower air dam and flows air threw the radiator then it is guided to the brakes, i would guess that the air flows through the drilled discs in this car to keep the discs cooler and prevent wear in long runs.

Porsche uses the Ceramic Composite rotors I mentioned in a previous response. I believe they come on the 911 Turbo and the GT2.
Most of the Le Mans cars I've seen run the carbon fiber-reinforced carbon rotors which, even if we could afford such a rotor, wouldn't be practical for street driving. No holes in those either.

-Mindgame

Originally posted by Mindgame
Porsche uses the Ceramic Composite rotors I mentioned in a previous response. I believe they come on the 911 Turbo and the GT2.


True but they are not standard on all models, only the $180K+ GT2. For example the std 911 Turbo still comes with crossdrilled iron rotors (the ceramic brakes are an $8K option). Normally I would "just say no" to crossdrilling as well but if they are cast into the rotor (the way Porsche and Brembo do them) then they're probably fine IMO.

FWIW you can run some Porsche uber-brakes (http://www.ultimategarage.com/bigbrake2.html) on your F-body if you so desire. Defintely not cheap though :eek: But then again neither is crashing into a wall if your brakes fade :D

Originally posted by Soma07
True but they are not standard on all models, only the $180K+ GT2. For example the std 911 Turbo still comes with crossdrilled iron rotors (the ceramic brakes are an $8K option). Normally I would "just say no" to crossdrilling as well but if they are cast into the rotor (the way Porsche and Brembo do them) then they're probably fine IMO.

FWIW you can run some Porsche uber-brakes (http://www.ultimategarage.com/bigbrake2.html) on your F-body if you so desire. Defintely not cheap though :eek: But then again neither is crashing into a wall if your brakes fade :D

Actually they are an $11,500 option on the 911 Turbo.;) One of the gents I work with bought one last summer... didn't get the option though. I wonder how many actually do?

On the subject of casting holes into a rotor... why do you think it would be better? Just curious.
As I see it, a cast hole has far more surface imperfection than one that's drilled with good tooling. The subject here being stress fracturing, I think that drilling w/chamfering would be preferred but that's just my thought. Any opinions?

-Mindgame

Originally posted by Mindgame


On the subject of casting holes into a rotor... why do you think it would be better? Just curious.
As I see it, a cast hole has far more surface imperfection than one that's drilled with good tooling. The subject here being stress fracturing, I think that drilling w/chamfering would be preferred but that's just my thought. Any opinions?

-Mindgame

The drilled and chamfered holes still have sharp edges, and you can't chamfer the inside of the hole. The drilling cuts through the grain structure, and free carbon in the iron can act like a void, which when you cut thru it acts like a stress riser. This is a good place for cracks to start with the constant heating/cooling cycles.

By casting the holes in you don't disturb the grain structure as much, and you could possibly have a smooth radius on both the inside and outside of the holes. The cost for the cores would be substantially more than even curved vane rotors, however.

Yeah, I always have an opinion.

Originally posted by Mindgame
On the subject of casting holes into a rotor... why do you think it would be better? Just curious.
As I see it, a cast hole has far more surface imperfection than one that's drilled with good tooling. The subject here being stress fracturing, I think that drilling w/chamfering would be preferred but that's just my thought. Any opinions?


Originally posted by OldSStroker
The drilled and chamfered holes still have sharp edges, and you can't chamfer the inside of the hole. The drilling cuts through the grain structure, and free carbon in the iron can act like a void, which when you cut thru it acts like a stress riser. This is a good place for cracks to start with the constant heating/cooling cycles.

By casting the holes in you don't disturb the grain structure as much, and you could possibly have a smooth radius on both the inside and outside of the holes. The cost for the cores would be substantially more than even curved vane rotors, however.


What he said :D

I was also basing my opinion off the experiences of some open track guys on a few other boards. Some of them were going through a set of stock LS1 or C5 rotors within a weekend untill they upgraded to one of the Porsche big brake kits. Now not only do they have better brakes but they're actually saving money because the rotors (and pads) last so much longer despite being crossdrilled.

I would love a set but 1. I'm poor and 2. I have a hard time justifying buying a set of brakes that are worth half as much as my entire car :eek:

Jon,
That explains the advantage to casting-in the holes pretty well. I've never really thought about it in that way... then again I look at things a little too simplisticly sometimes. Thanks for the info.

Jason,
I have a set of Wilwood SL-6R calipers and hatted & slotted-rotors on my C5. I don't do any auto crossing with the car but the stopping power is night and day difference from the stockers. When you consider the safety aspect to having a much shorter stopping distance they are well worth every penny. Especially when you start adding more 'go' to your ride.
I can understand the broke college kid thing though. Been there, done that and drove a 4-door 65 Falcon while I did my tour. At least you have a cool car.:D

-Mindgame

Originally posted by Mindgame
Jason,
I have a set of Wilwood SL-6R calipers and hatted & slotted-rotors on my C5. I don't do any auto crossing with the car but the stopping power is night and day difference from the stockers. When you consider the safety aspect to having a much shorter stopping distance they are well worth every penny. Especially when you start adding more 'go' to your ride.


I fully agree you should always have more 'whoa' power than 'go' power. I'm just always looking at the bang for the $$$ aspect which is why I put a set of LS1 brakes on my car. I really felt the stock LT1 brakes were totally inadequate for a 3500lb car capable of 150mph. BTW how do you like the Wilwoods? I was thinking about getting them in the way distant future but I hear they dont have dust seals which makes them semi-unsuitable for steet use.

If you have the chance try an auto-x event sometime, its alot more fun (and difficult) than it looks :cool: Suprisingly its really not hard on brakes since all the runs are only about a minute long and you you're only braking from ~60mph tops.

I can understand the broke college kid thing though. Been there, done that and drove a 4-door 65 Falcon while I did my tour. At least you have a cool car.:D

Thanks! At least my college days will be over in a few months :D

Originally posted by Mindgame
Jon,

I can understand the broke college kid thing though. Been there, done that and drove a 4-door 65 Falcon while I did my tour. At least you have a cool car.:D

-Mindgame

ZDriver96 <----- broke college student.
I wanted the C5 brake upgrade so bad but 800 bucks.... just cant see that right now. I picked up some virtually new LS1 brakes upgrade with steel braided lines for 180 bucks.. Ill pick up some really good pads to stop better too.
I valet cars part time and i get to test out lots of cars :)
98+ f bodies brake a lot better than 93-97.

Originally posted by Soma07
I fully agree you should always have more 'whoa' power than 'go' power. I'm just always looking at the bang for the $$$ aspect which is why I put a set of LS1 brakes on my car. I really felt the stock LT1 brakes were totally inadequate for a 3500lb car capable of 150mph. BTW how do you like the Wilwoods? I was thinking about getting them in the way distant future but I hear they dont have dust seals which makes them semi-unsuitable for steet use.

I really like the Wilwoods.. of course I don't have anything to compare them to except for the stockers, lol. I also ran Wilwoods on the 68' Camaro I sold here 2 months ago. Again nothing for comparison but the stock disc setup.. sad, sad.
Now, the issue with the pistons... I talked to a gent at Wilwood because I had heard similiar things. He told me that a little maintainence would go a long in ensuring the seal life. Basically he recommeded that I spray the pistons with brake cleaner once a month and that I inspect and/or replace the seals every year. I don't really mind doing that sort of thing anyway so I don't consider it much of a hassle. Not to mention, I only put about 5k a year on my car. I like the quality of Wilwoods (higher end) stuff... not cast like alot of the others but fully machined. Truly a work of art and compared to Brembo, they're a deal.

If you have the chance try an auto-x event sometime, its alot more fun (and difficult) than it looks :cool: Suprisingly its really not hard on brakes since all the runs are only about a minute long and you you're only braking from ~60mph tops.

I do track days on the GSXR750 and that's really enough for me. I prefer the straight line stuff when it comes to cars. Now I have thought about the Silver State races... those would be a hell of a lot of fun I think. Again, you need some driving skill and that's not anything I care to pretend I have.;)
Now if I could get into a purpose built race car... preferably something along the lines of those little Indy car lookalikes with the GSXR1300 engines in them... I'd be game for that on a really tight track.:D

-Mindgame