Slotted rotors vs. drilled

[MVZ944T]

Anyone have any experience in using slotted rotors vs. the stock drilled rotors in a racing applications. If you do, any suggestions will be appreciated. Stock Porsche rotors are only getting me about a year +. How about cryogenic treated rotors, are they still available?

Mike VZ

[ttweed]

Mike-

I have found the tech articles at the Stoptech site to be very helpful in understanding issues with current braking systems.

This is what one of their white papers has to say about drilled vs. slotted:

"For many years most racing rotors were drilled. There were two reasons - the holes gave the "fireband" boundary layer of gasses and particulate matter someplace to go and the edges of the holes gave the pad a better 'bite'.

Unfortunately the drilled holes also reduced the thermal capacity of the discs and served as very effective "stress raisers" significantly decreasing disc life. Improvements in friction materials have pretty much made the drilled rotor a thing of the past in racing. Most racing rotors currently feature a series of tangential slots or channels that serve the same purpose without the attendant disadvantages."

The holes in Porsche OEM "drilled" rotors are not actually drilled, but cast into the iron blank during the manufacturing process. The edges of the holes are then carefully champhered on both sides to prevent the stress risers around them. Cheap rotors that are actually drilled after casting would be much less satisfactory, and cracking is still a problem even with the OEM ones. I have always used the slotted rotors myself.

I know that cryogenic treatments are still available, but I have never used them and I am not sure that they offer a cost benefit over untreated.

TT

[kary]

I have not used the slotted mainly because they do not offer them in my 993 brake size. In the big reds you can get slotted rotors. I have heard that slotted are better and in fact the drilled rotors do crack quite easily with the heat, but after running both frozen rotors and OEM rotors over a entire year on the same tracks, the frozen rotors definitely cracked less and last longer. How long, maybe 25% longer. Once you calculate the additional cost of the frozen rotor versus OEM or Zimmermann, it might not be worth it other than the hassle of changing rotors more often, which is not that hard anyway.

[ttweed]

How long, maybe 25% longer. Once you calculate the additional cost of the frozen rotor versus OEM or Zimmermann, it might not be worth it other than the hassle of changing rotors more often, which is not that hard anyway.

That was my take on it when I checked the last time, Kary. It was going to be $50/ea. to get my rotors cryo-treated, and they cost about $80. If they lasted twice as long, it would be worth it. For 25% life extension, probably not.

[Jad]

I ran both slotted and drilled on my n/a 944 and the slotted were much better as the drilled cracked a lot. Couldn't tell a difference in actual stopping ability and my turbo only has flat disks which also seem to work fine and never crack for my usage.

To a large degree, stopping wears material so your pads can be hard and wear the rotors or soft and wear themselves out. For optimal braking, new pads and new rotors are best, so even wear between the two may be the goal.

Another interesting point, some tuner TV show was tricking out some car and did a lot of dyno runs. After getting a base line, they installed some nice big rotors to replace the wimpy factory brakes. The upgrade actually cost them 10 hp due to all the rotating mass Can you really make up for the added unspring weight with better braking????

If your brakes are getting hot, that can also reduce life, so maybe more cooling would be a possible answer, though it tends to increase drag.

So most everything is a tradeoff. Bigger is not always better. If you are happy with the way the car stops, be careful doing too much to keep from having to replace rotors as often.

[kary]

How long, maybe 25% longer. Once you calculate the additional cost of the frozen rotor versus OEM or Zimmermann, it might not be worth it other than the hassle of changing rotors more often, which is not that hard anyway.

That was my take on it when I checked the last time, Kary. It was going to be $50/ea. to get my rotors cryo-treated, and they cost about $80. If they lasted twice as long, it would be worth it. For 25% life extension, probably not.

Tom, not sure but I think it might be cheaper to order from Frozen Rotors themselves versus asking someone else to feeze them.

[MikeD]

I had OEM rotors chryo treated. Like Tom said, didn't seem to be worth the $$$. Will not do that again. Might order Frozen Rotors if they are not a lot more.

One of these days I will look for slotted rotors that fit my car. I have not, yet replaced my rotors due to wear, but always due to cracking .

As I understand it, the larger brakes do not increase your stopping ability. You can lock em up with Toyota Corolla brakes. But I wouldn't want to do more than one lap at Cal. Speedway with them. The purpose of the larger brakes is additional cooling and heat disbursement. Big Reds would be highly desireable for an enduro, but not so desireable at an AX.

[ttweed]

Tom, not sure but I think it might be cheaper to order from Frozen Rotors themselves versus asking someone else to feeze them.

Just checked current prices and it is $121 to buy from Frozen Rotors the cryo-treated version of the Ate Powerslot rotor you can buy at the discount houses for $79, so the differential is $42 rather than $50. Still about a 50% premium. If it doubled the life it would be very much worth it, but I haven't heard that kind of result from anyone yet. The company claims it is 100-300%, but no one I know in real life has confirmed such performance, so I'm still on the fence about it.

TT

[MVZ944T]

Thanks for info guys. I met a guy at the last NASA vent with a very high tech Mustang. His brakes were made by a guy up in Camarillo. The BrakeMan. He has been running the same rotors, no slots, no holes, and no cooling hoses, for 2 years and they looked perfect. I checked out the site today. Rotors are laminated steel. They claim they will not crack and it appears that may be true. Downside, $900 per rotor. I'll check out the frozen rotors I think.

[David J Marguglio]

a very high tech Mustang

There is such a thing???

[MVZ944T]

What can I say, you had to see it. I would say the GTO's that TRG is running in the Grand Am and kicking butt are fairly high tech also.

[MikeD]

What can I say, you had to see it. I would say the GTO's that TRG is running in the Grand Am and kicking butt are fairly high tech also.

You'll have to forgive Dave, Mike. He hasn't been to a track in so long I think he forgot what a real racecar looks like.

[mnettles]

chiming in on frozen rotors- I tried a set and did not get any significant improvement in longevity.

mj

[MVZ944T]

By the way Dave,

where is that new race car of yours anyway?