Boxster brake upgrade for 911s kit development

[quaz]

Here is the deal, for the last couple of years I have tinkered around with developing a real cost effective brake upgrade for 911s. As everyone points out the problem with slapping Boxster calipers on a 911 is the rotor is no larger than the stock Carrera rotor. So other then having a bit more clamping force and swept pad area heat dissipation is not improved. Larger rotors require modifying the hub, changing wheel offset or going to floating rotors. All of those options have trade offs, price and compromises. Oh yeah and if you have early struts with 2.5" spaced mounting ears you need new struts.

So what did I work on? I wanted better calipers, braking bias to remain stock, larger rotors, all bolt on without new hubs or struts, clears 16" wheels and reproducible. After goofing around for a couple of years I installed 2 kits. One on my car and one on my friends 70. Between the two of us we only have about 500 miles total on the setup. However so far the results are great. Oh yeah and both cars have the 2.5" strut mount spacing.

Here is my dilema, I don't have the time, resources or contacts to produce this kit and resell it. Ideally I would like to find someone in the Chicago/Milwaukee area that can help me finish the testing, work out sourcing bugs and figure out how to market this kit. My goal isn't really to make money on this, but to make my development time available to other Porsche owners.

Here are some pics of what this looks like.





This is a 300x26mm rotor that bolts to the stock hub with the stock offset and caliper adapter for a Boxster caliper. Paired with rear Carrera calipers/rotors it maintains the stock braking bias and clears 16" wheels. It will not clear a 15" wheel. The pics above show the rotor size difference to stock. Because the rotor is larger it allows the caliper to move up enough to clear the 2.5" ears by just trimming the edges of inside pad. Swept area remains unchanged. This will fit the 3" ears perfect with no issues.

Feel free to ask me questions. PM if you are in the area and interested in helping me finish this project. Ideally I would like to try this out on 2 more cars this summer and one of them do some racing. I have a bit of money invested in this along with a lot of time. I just don't want my effort to go to waste as it will benefit the community in the long run.

[Bill Verburg]

Looks like a nice reasonable setup intermediate to stock and 930s

the bias will be pulled a little further forward than the old stand by Boxster on Carrera rotors because of the larger front rotor diameter but not by enough to worry about, you could probably use Boxster S/996 calipers(originally these were on 318x28 rotors.

as usual a 23.8mm m/c would be advisable but not absolutely necessry

[Elombard]

I would like to try it on my 84. I can get the calipers. What is involved with the rest of it?

[quaz]

Bill hit the nail on the head. This is an intermediate step between stock and 930. It is possible for the larger S/996 calipers to be bolted on, but I want to get this setup worked out first. There are a lot of different options out there for "big brake" kits. This is more of an upgrade to the aging original setup.

Anyway, I need to find someone local to work with on trying this out on an SC or S. Again, if there is someone in the Milwaukee/Chicago area with an interest in a summer project let me know.

[toddu]

I'm sure you'll get plenty of local volunteers, but I just put a 300hp short stroke in my SC and could use a little more wooo.

Todd

[Elombard]

Can you post the size differences from the stock stuff if you know it off the top of your head? I could look it up I guess. Love that you addressed the larger rotor concern. Really want the extra heat capacity if going to a bigger caliper. Any idea what the cost would be for rotors and adapters once the kit is sorted out? The rotors dont look terribly expensive?

[quaz]

For comparison here is the breakdown on rotor sizes:

Stock early-S-SC
282x20mm

Carrera
282x24

930
304x32

Boxster upgrade test (mine)
300x26

As for cost ideally the rotors should be about $100 each for a good quality one. $150 if they are heat treated and drilled. So about the same as stock. The cost of the adapters would probably be about $400 if they included all the mounting hardware and possibly new hard lines. Figure with a set of Boxster calipers you could do the front upgrade for less then $1K. In the rear the Carrera rotors and calipers are a perfect match and maintain the bias. Stock bias is 1.6 and Boxster/Carrera is 1.64. However Bill is correct that with the larger rotor it will probably be a smidge more front biased. So like 1.66ish????? For comparison an all Boxster setup would yield 1.72.

[quaz]

Quick pic of the entire upgrade I put on my car.

[Bill Verburg]

Originally Posted by quaz

For comparison here is the breakdown on rotor sizes:

Stock early-S-SC
282x20mm

Carrera
282x24

930
304x32

Boxster upgrade test (mine)
300x26

As for cost ideally the rotors should be about $100 each for a good quality one. $150 if they are heat treated and drilled. So about the same as stock. The cost of the adapters would probably be about $400 if they included all the mounting hardware and possibly new hard lines. Figure with a set of Boxster calipers you could do the front upgrade for less then $1K. In the rear the Carrera rotors and calipers are a perfect match and maintain the bias. Stock bias is 1.6 and Boxster/Carrera is 1.64. However Bill is correct that with the larger rotor it will probably be a smidge more front biased. So like 1.66ish????? For comparison an all Boxster setup would yield 1.72.

1)the torque ratio for stock A/M('69-83) setup on stock rotors is 1.491(@70bar line 1444/969nm)

2)the torque ratio for an all Boxster setup on 3.2 Carrera rotors is 1.607(@70bar line 1815/1130nm)

3)the torque ratio for an l Boxster front setup on 3.2 Carrera rotors w/ stock 3.2 Carrera rears is 1.534(@70bar line 1815/1183nm)

I would need to do a little more research but this setup would be in between 2 & 3

[michael lang]

Kevin, what were you measuring when you said "However so far the results are great"? How much did your mods change the characteristics of your car and what did it do to your laptimes? Also, did you monitor temps not only with your set up but before you did the bolt on? If so, what was the difference?

[quaz]

Mike, on two cars there are maybe 500 miles total of drive time. We got them done right as the weather went south last fall. No track time and neither car has seen the road this year yet. I was hoping to find someone local to log some track time and get some empirical data. Also want to know how all the parts hold up to stress. Hence the feeling for some help to finish off the project.

As for drive feel, they have a lot more power. Locking them up is no problem at all and I don't need as much pedal effort to bring the car down from speed. With the stock calipers I always felt a little unsure of the brakes and it took a lot of effort to lock them. I felt the same way on my 928S2 before I upgraded it to S4 brakes.

[michael lang]

What else is needed, 17/18" wheels? (I know that you said you wanted them to clear 16" wheels) 23mm master cylinder? Cooling ducts?

[quaz]

They clear 16" wheels perfectly. 19 or 23mm master cylinder will work.

[MotoSook]

You might try the guys on the Chicago yahoo email list. We're mostly track junkies. I'd post a link but I'm on my mobile now. Send me an email, and I'll send an invitation.

[KTL]

Originally Posted by MotoSook

You might try the guys on the Chicago yahoo email list. We're mostly track junkies. I'd post a link but I'm on my mobile now. Send me an email, and I'll send an invitation.

Souk is right. Plenty of track junkies around our area to help you out. I've got a car I can test these on as well.

I'm sort of a brake nerd, so i'd be glad to assist with this.

[euro911sc]

What rotor are you buying? I just put on 964 calipers and will use up my old Carrera rotors, but am looking for a slightly larger rotor that will fit my setup.

[Elombard]

I am thinking those are the "proprietary"part. They almost have to be custom dont they? Or did he find an off the shelf rotor that happens to fit? The front 911 rotors seem like they are different from most rotors hard to imagine there is a similar one out there that has not been discovered.

[JJ 911SC]

Originally Posted by quaz

Quick pic of the entire upgrade I put on my car.

Kev,

This look great. By the time all the bugs are work out, I'll be ready.

Hang in there

[Craig_D]

I hate to ask, but what's the difference between SC rears, and Carrera rears? I've upgraded my SC to Carrera fronts disks and calipers, but I'm interested in calipers with less weight than the Carrera ATEs, so the Boxster setup looks attractive (if it is lighter with similar braking and head dissipation), and I still have the SC rears on new SC rotors.

[MotoSook]

Originally Posted by Elombard

I am thinking those are the "proprietary"part. They almost have to be custom dont they? Or did he find an off the shelf rotor that happens to fit? The front 911 rotors seem like they are different from most rotors hard to imagine there is a similar one out there that has not been discovered.

Rotor looks shaved on one side in this picture, unless it's a photographic illusion. Perhaps there is a rotor that is close to the offset needed, shaved one side, put bolt holes in it to match hub and you got something like this?