New OEM Cross Drilled Rotors for the Base Boxster

[blinkwatt]

Found these today;
http://e-partssales.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=P&Product_Code=98735140101andL98735140201&Category_Code=98625brakes

They claim they fit on a base 986 even though they are a base 987 part. They are also the same price as the none drilled front OEM rotors. Is the braking system on a 987 the same as the 986? Anyone try these yet? How about the part numbers for the rear OEM cross drilled rotors?

[chaudanova]

Interesting, I'd like to know this as well....

Did you notice that the drill pattern is different on the two rotors pictured?

[blinkwatt]

Just to note the Front Cross-Drilled OEM rotors are $96.58/each (California Pricing).
No one at Sunset even knew they had cross drilled rotors for the base Boxster and they couldn't find the rear matching part #s either.

[J-RAD]

There are no cross-drilled OEM rotors for the base model.

In addition, going to a cross-drilled rotor with the OEM base design means that you are reducing the swept surface of the rotor and likely to increase your braking distances (ie. decrease effectiveness).

[blinkwatt]

Just got off the phone with Rick @ Suncoast.

The base 986 & 987 share the same brake rotor size for the front and that's why the 987 rotors fit on the 986 set up.

The rear base 986 & 987 e-brake set up difference thus not allowing the 987 rotors to fit on a 986.

He said you could match up rear Zimmerman cross drilled rotors with the front OEM cross drilled rotors. He said the only difference he has noticed(from his own experience) is that the Zimmermans don't last as long.

[Chippy]

Not sure if these are of interest, they're available in the UK but guess they'd ship to the US, plus you'd get the 17.5% off the price for the UK Tax.

I'm thinking of going for these when I replace my crappy 16" wheels.

http://www.blackdiamondbrakesonline.co.uk/

[insite]

Originally Posted by chaudanova

Interesting, I'd like to know this as well....

Did you notice that the drill pattern is different on the two rotors pictured?

the one on the left is a rear and the one on the right is a front. the fronts are directional (different from left to right) while the rears are not.

[Even Steven]

Originally Posted by J-RAD

There are no cross-drilled OEM rotors for the base model.

In addition, going to a cross-drilled rotor with the OEM base design means that you are reducing the swept surface of the rotor and likely to increase your braking distances (ie. decrease effectiveness).

On the 986 or the 987? The 987 I looked at was a base w/cross drill rotors.

[porsche986spyder]

Originally Posted by J-RAD

In addition, going to a cross-drilled rotor with the OEM base design means that you are reducing the swept surface of the rotor and likely to increase your braking distances (ie. decrease effectiveness).

I don't agree with that. The only thing cross drilled rottors due is keep the rotors cooler. The surface area is what counts for braking distance. And if they are bigger than the stock O.E.M. base model then it should be better. Best of all would be a set of cross Drilled & Slotted(for venting brake dust/gasses to escape) rottors for better cooling and venting. You should upgrade the pads too while your at it.

[chaudanova]

Originally Posted by insite

the one on the left is a rear and the one on the right is a front. the fronts are directional (different from left to right) while the rears are not.

Ohhhhh, okay gotcha. Thanks for clearing that up

[J-RAD]

Originally Posted by Even Steven

On the 986 or the 987? The 987 I looked at was a base w/cross drill rotors.

Sorry, should've clarified. 986 only. He has a '99 so I was responding specifically to that.

[J-RAD]

Originally Posted by porsche986spyder

I don't agree with that. The only thing cross drilled rottors due is keep the rotors cooler. The surface area is what counts for braking distance. And if they are bigger than the stock O.E.M. base model then it should be better. Best of all would be a set of cross Drilled & Slotted(for venting brake dust/gasses to escape) rottors for better cooling and venting. You should upgrade the pads too while your at it.

Cross-drilled rotors do nothing in the way of cooling. In fact, removing that material allows for an increase in heat since that space is not available for dispersing heat.

Rotors need to do two things well. First, they must disperse heat. Second, they must dissipate that heat. In addition, they must have the appropriate amount of surface area.

The mass of the rotor assists with heat dispersal. It takes much more energy to heat a large item than it does to heat a small item. As brake force is applied and things heat up, the heat is able to be distributed throughout that entire mass. If you remove some of that material, which is the case when rotors are cross-drilled, you not only have removed material that assists with dispersal (this may actually result in increased temp) but you've also reduced your swept area (cross-drilled rotors typically have ~85% or so of the surface area that a solid/blank rotor will have – ie. 15% less).

So, decreased mass results in a lesser ability to distribute heat energy thoughout the rotor, thus making it less "efficient" at dissipating heat, which in turn results in increased rotor/pad temperatures and reduced braking performance.

In addition, there is an additional point of heat stress, which of course means it’s a risk to structural integrity. If you look at used cross-drilled rotors from a race car (this is becoming rare...not to mention they may use different materials) you may notice heat cracks originating from the holes (you’ll also notice they throw these away after just about every race...how practical is that?).

As for the swept area, the more friction that can be generated between the rotors surface and the brake pad, and greater energy transfer (stopping power) can be obtained. A smooth surface will help insure that more of the pad surface area is in contact with the rotor.

The only way a cross-drilled rotor will make a difference in overall braking is if you increase swept area and/or increase the mass to make up for the material that was removed. Again, you need to account for heat dissipation and maintain braking surface area.

So, the key to your statement is that he has to go to a larger size drilled rotor to acheive the same braking effect as a solid rotor. Unless the size of the rotors are increased, you've done nothing to improve your braking.

A few mildly interesting sources of information that relate to the topic:
http://www.thebrakeman.com/rotortech
http://www.raceshopper.com/tech.shtml#brake_performance

Also for arguments sake, take a look at these braking distances (both test results according to R&T):
'00 Porsche Boxster S - cross-drilled standard
F: 12.5 (diameter) x 1.1 (thickness)
R: 11.8 X 1.0
Braking distance
From 60 to 0- 125 ft.
From 80 to 0 - 219 ft.

'99 Porsche Boxster - solid standard
F: 11.74
R: 11.5
Braking distance
From 60 - 121
From 80 - 214

Notice that not only is there no improvement in the S' braking distance, it's slightly longer than the Boxster's, albeit only a few feet - this despite larger brakes. A couple points worth noting here: The curb weight of the Boxster is 2811 lbs., the Boxster S is 2910 lbs. There is admittedly almost a 100 lbs difference. However, the Boxster S that was tested had the larger wheel/tire package than the standard Boxster meaning it potentially had a better footprint/stopping capability.

When you get down to it, cross-drilled rotors are more about marketing than anything else.

[blinkwatt]

Originally Posted by J-RAD

Cross-drilled rotors do nothing in the way of cooling.

If that's true then why does every car in Le Mans use them?

[racer_d]

How many times have we hashed this over

One advantage to the cross drilled units is their ability to vent heat and gasses away from the surface area which has already been mentioned.

Will this make an impact in "street" driving? or a few highway stops? no, not really. But, in racing applications, managing HEAT of brakes is very important. When you are slowing the car down 10-20 times per lap for dozens to hundreds of laps, the amount of heat created can be extreme (1200-1500 degrees). Anything that helps lower this temp and allows the brakes to "last longer" at a higher efficency is worth doing. Hence their use on race cars. On street cars, it is more "marketing" to show a link between what is learned/used in racing and what can be used on the street.

In a pure "street" application, changing compounds of brake pads and tires (since this is what the brakes are "connected to") will have a greater impact in stopping distances than changing to slotted or drilled rotors, especially if they are the same size as the stock units.

[J-RAD]

Originally Posted by racer_d

One advantage to the cross drilled units is their ability to vent heat and gasses away from the surface area which has already been mentioned.

Venting boundry layer gases (as well as water and dust) away, yes. Venting heat, no. Cooling is what the vents are for (between the discs). The drill holes and/or slots help keep the brake pads clean. Drilled rotors may also possibly reduce rotating weight.

To quote the raceshopper site I listed above: "What handles more heat- A cast-iron kettle or a pizza pan with holes in it?"

Darrick Dong; Director of Motorsports at Performance Friction: "Anyone that tells you that drilling makes the disc run cooler is smoking crack."

Grassroots Motorsports (Feb 2001): "Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the ’40s and ’50s, not a whole lot. Rotors were first drilled because early brake pad materials gave off gasses when heated to racing temperatures, a process known as “gassing out.” These gasses then formed a thin layer between the brake pad face and the rotor, acting as a lubricant and effectively lowering the coefficient of friction. The holes were implemented to give the gasses somewhere to go. It was an effective solution, but today’s friction materials do not exhibit the same gassing out phenomenon as the early pads.

For this reason, the holes have carried over more as a design feature than a performance feature. Contrary to popular belief, they don’t lower temperatures. (In fact, by removing weight from the rotor, they can actually cause temperatures to increase a little.) These holes create stress risers that allow the rotor to crack sooner, and make a mess of brake pads—sort of like a cheese grater rubbing against them at every stop. Want more evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it.

The one glaring exception here is in the rare situation where the rotors are so oversized that they need to be drilled like Swiss cheese. (Look at any performance motorcycle or lighter formula car, for an example.) While the issues of stress risers and brake pad wear are still present, drilling is used to reduce the mass of the parts in spite of these concerns. Remember that nothing comes for free. If these teams switched to non-drilled rotors, they would see lower operating temperatures and longer brake pad life, at the expense of higher weight. It’s all about tradeoffs."

[J-RAD]

Originally Posted by blinkwatt

If that's true then why does every car in Le Mans use them?

They don't.

Most pro race teams don't use cross-drilled rotors anymore. They use solid carbon, slotted, or other advanced technologies. As an example:

These are from the RS Spyder:


And here is a photo from the 997 GT3RSR:




The Audi R10's rotors:

[blinkwatt]

Originally Posted by J-RAD

They don't.

Most pro race teams don't use cross-drilled rotors anymore. They use solid carbon, slotted, or other advanced technologies.

I stand corrected. It has been 2 years since I went to a ALMS event,lol I'm old and outdated at 19 years old.

[porsche986spyder]

Well, if you look at what I said earlier, the best of both worlds, Cross-drilled & Slotted would be the best as long as the surfaace area is larger than the stock application rottors. In which most cases, just about any aftermarket performance rottor that you buy to replace the stock ones are usually bigger. Never seen an aftermarket rottor that was the exact same size as the stock one, like someone said earier that would defete the purpose of having them cross-drilled or slotted. :ah:

[insite]

Originally Posted by porsche986spyder

Well, if you look at what I said earlier, the best of both worlds, Cross-drilled & Slotted would be the best as long as the surfaace area is larger than the stock application rottors. In which most cases, just about any aftermarket performance rottor that you buy to replace the stock ones are usually bigger. Never seen an aftermarket rottor that was the exact same size as the stock one, like someone said earier that would defete the purpose of having them cross-drilled or slotted. :ah:

the best scenario is a solid or slotted rotor with cooling ducts. better airflow will do more than just slots or holes.

most racing teams avoid drilled rotors anyhow. drilled rotors tend to not handle heat quite as well as solid or slotted rotors. they are more prone to hot spots; this causes the ferrous material to change to austenite, which is harder than the surrounding material. this in turn causes high / low spots on the rotor, ultimately leading to poor surface mating between the pads / rotors. this problem is exacerbated by the ferrous pad material used in most race linings.

[J-RAD]

Originally Posted by porsche986spyder

Well, if you look at what I said earlier, the best of both worlds, Cross-drilled & Slotted would be the best as long as the surfaace area is larger than the stock application rottors. In which most cases, just about any aftermarket performance rottor that you buy to replace the stock ones are usually bigger. Never seen an aftermarket rottor that was the exact same size as the stock one, like someone said earier that would defete the purpose of having them cross-drilled or slotted. :ah:

But then you're looking at a complete brake system upgrade. You'd also need to get larger calipers, a new master cylinder, new pads, and so on....you understand.

Actually, most of the aftermarket rotor applications I've seen are indeed the same size. Essentially, they've just simply taken a rotor blank and drilled it.

Nonetheless, I'll say this about cross-drilled rotors...they look cool!