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.

 

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

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.

 

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

 

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

 

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 on your F-body if you so desire. Defintely not cheap though But then again neither is crashing into a wall if your brakes fade

 

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

 

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.