Drilled rotors...front only. Budget dictates?

FlaCarrera · 08-04-2002, 06:29 PM

First DE coming up. (2.2 mile road course) Upgrade budget funds depleted for awhile. Am pondering drilled rotors and new pads for front ONLY. Stock rotors and pads replaced April '02...less than 600 miles. Opinions please on:

A) Don't worry, fresh stock brakes OK for first DE? B) Drilled rotors in So. Florida mid-August heat....DE will be helpful, even if front only C) If you go with drilled rotors, go with front and back...NOT just front? BTW, have SS brake lines.

Thanks....

Ted in So Fla.
86 Carrera Targa Blk/Blk

Bill Verburg · Bill Verburg's Garage

Don't waste your $ on the aftermarket drilled rotors that are currently available. Since your rotors and pads are relatively new and hopefully properly bedded in, just make sure that you have fresh high temp fluid.(Sherwood Lee has a nice summary of brake fluids here

You can also fashion a simple scoop as described here which will help(that is if you do not already have some sort of brake ducts)

If you must buy something, buy a set of high temp pads for use only at there track. I like Pagid orange but there are numerous others that may perform as well. They are generally poor choices on the street because of low temperature friction characteristics and noise, but they are just the ticket for track days.

zotman72 · 08-04-2002, 08:22 PM

I just finished a DE this weekend here in Colorado. I destroyed my ATE slotted rotors with a set of Hawk Blue Racing pads. These rotors had lasted two years (no discernible wear) with street pads (PBR, Ferodo, Porsche OEM etc.) with M calipers. Now with SC calipers, I have lost the slotted grooves in two track days! Also I learned an important lesson-- Do not mixed race pads (front) with stock pads (rear) to save money. My car was nearly impossible to control under braking--> immediate front wheel lockup with hand of God stopping (binary, on/off). What a mess, I probably will go back to street pads or try a more rotor friendly race pad on both sets of wheels next time. HTH somebody. I always seemed to learned these things for myself.

GeorgeM · GeorgeM's Garage

Not sure about Ate, but Brembo rotors seem to hold up real well.

As far as pads go, Hawks seem to be some of the least rotor friendly pads. I used the Blues for a whole season and, although my stock Zimmerman rotors held up okay, the brake dust wasn't dust, it was visible metal shavings. I liked the stopping performance, but not so much the abrasiveness of the pads.

I'll concur with holding off on the drilled rotors. Use what you have until they wear out, especially if they're fairly new. I ran on stock rotors for 20 DE events using Hawk Blue and PFC 80/97 pads, and they held up well.

I'm with Bill on brake cooling as well. For the price of a set of drilled rotors, you can get a Cool-Brake kit.

Have fun!

Bill Verburg · Bill Verburg's Garage

The '84-89 Carreras use a thicker rotor than earlier versions 24mm vs 20mm, the thicker rotor will hold up better than the thinner variety. I don't remember seeing Brembo 20 or 24 mm rotors for 911s, could be wrong though(George,you have 20 or 24mm Brembos?). The most common are Zimmerman and ATE, both were oem suppliers. Yes, race pads will tear up rotors faster than street pads, and they will thermally stress the rotors to a greater extent, that is why you need cooling and change them out for street use. The ultimate solution is the 930/964/993 setup. the street pads on the other hand will glaze easily giving you almost no brakes hot or cold. Choose your poison

GeorgeM · GeorgeM's Garage

No Bill, I do not have Brembos, I have Zimmermans.

I just got a 930 setup and got Brembos for that, so I made a poor assumption that they also make rotors for the Carerra.

My Zims have held up surprisingly well with all the DE events over the last 2 1/2 years. I do have brake cooling, so I'm sure that has helped longevity to a certain extent. I've been pleasantly surprised.

beepbeep · 08-05-2002, 04:51 AM

Ditch drilled rotors (especially if they are drilled and not cast) , they will just crack around the holes.

Go with stock rotors, race pads both front and back and some sort of air-scoop to keep them cool (essential!)

Bill Verburg · Bill Verburg's Garage

George, Just curious, where did you get the Brembo 930 rotors? Are they 2 piece, 304x32F & 309x28R? floating? price? I am trying to collect all relevant info in one spot. Feel free to contact me privately if you wish confidentiality.

cstreit · cstreit's Garage

I'll 4th the notion to forget drilled rotors. They will crack. THe only thing they really help with is shedding water in the rain. Yes, the holes also help release some out-gassing from the pad, but slotted will hold up longer without cracking.

SUre, they look great, but they always crack...

I'll relate a few stories of cracked rotors on the track some time from a friend...

I use factory rotors in my racecar, even in the rain... Most good pads have a slot in them to help with the gassing...

Don Wohlfarth · 08-05-2002, 06:56 AM

Ted, the only thing you should do before your 1st de is change the brake fluid to ATE Blue/Gold. You already have new pads and rotors which will be fine. Don't do anything to else to your car, learn to drive it as it sits. It usually takes some serious seat time for a driver to learn to drive a car on track and Porsche offer more performance so it may take awhile before the car becomes the limiting factor in performance driving.
Zotman, why did you go to SC calipers from the M? Did you need more brake, overheating, what? From your description it sounds like you have entirely too much brake on the front. To compound your problem you have a more aggressive pad than you have used on the front. The SC brakes and Blue are doing exactly what they're supposed to, stop the wheel from turning. Having a stock pad and probably stock M calipers on the rear have greatly reduced the rear brakes ability to help slow the car.
Installing one type of pad in the front and a different pad in the rear is pretty common. However it is usually a bandaid because of a problem of not using the correct calipers front and rear. You want the larger caliper in front as it will do the majority of the braking and a smaller caliper in the rear. If you do not have the ability to adjust the brake bias you will either have to change the caliper or you could use a less aggressive pad in the rear. It is nothing more than a tuning tool.
Your problem sounds like you have pretty much eliminated all rear brake. You may find that installing a less aggressive pad in the front and a more aggressive pad on the rear may help with your current problem.

zotman72 · 08-05-2002, 07:41 AM

Don and others: I needed more brakes as my T is really an S now and my little M calipers were not really doing the job last season at the track. Hence, new RSR struts and a set of rebuilt SC brakes up front this year. I should have just got used to the SC brakes (same size pads as S calipers) with street pads first ----which I did use for one track event this year but I wanted to try race brakes right away and went with the Hawk pads. Hence the brake bias disaster I experienced this weekend at our Mountain View (CDR) track. I did have cooling ducts in place but I do not think that was the issue....

Bill

At least I provided entertainment for the corner workers on several extreme braking locations on that track.

FlaCarrera · 08-05-2002, 08:05 AM

Budget will allow for upgraded pads (Hawk hps or hp plus)& Blue brake fluid.

Will the air scoops which ad copy says cool the oil cooler also work to help cool the (front) brakes? The scoops which go where side marker lights normally live. Looks like a good way to get a lot of air flowing in that whole front wheel well neighborhood. We're talking a ambient heat index of 100+ not to mention what the track temp will be?

May $queeze the cookie jar and get a strut tower bar too.

Thanks for all the advice so far.
Cheers
Ted in So Fla
86 Carrera Targa Blk/Blk

Bill Verburg · Bill Verburg's Garage

The scoops in the lights give a little more air, but not enough air. Did you check the link on brake cooling that I supplied, there is also a link to a 964/993 scoop that will also work and can be cheaply done.

Bill Verburg · Bill Verburg's Garage

zotman72,
The basic hydraulic bias on your car with SC rotors and A front/M rear calipers is 1.596. The range of bias that most people find useful for street/track use w/o p/v is ~1.5-1.9, for autocross ~1.2-1.7 depending on other factors such as tires,suspension, pads etc.

By using the race pads front the total brake torque went way up at the front. As Don pointed out using different pads f/r is a common practice, used to correct some sort of other bias problem which you don't have.

I think that the stock size slotted rotors used w/ either race or stock pads will give you good results. Your car is farly light so that set up w/ cooling ducts/scoops will probably suffice. If not the next step up for you would be wide A calipers from an '84-89 Carrera and 282.5x24mm rotors from the same car(slotted off course!), used with your existing rear caliper/rotor.