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Porsche Boxter Brakes ?
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OhChit
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PostPosted: Sun Aug 09, 2009 5:26 am    Post subject: Porsche Boxter Brakes ? Reply with quote

I have a complete Set of Porsche Boxster Brakes that I would love to install onto my Suby powered 1987 Westy.. Only problem is how do I do it? Also my wheels are the 5x112 Mecedes so I want to keep them. I guess I'm looking at some sort of bracket for the Calibers, and Rotors with 5x112 lug paterns. But how do I get this to work?
Any help would be appricated.
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Dingchowping
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PostPosted: Sun Aug 09, 2009 11:51 am    Post subject: Reply with quote

Hi OhChit,

Do you have standard Boxster or Boxster S calipers? I'm in the process of installing Porsche "Big Red" brakes from a 993 Twin Turbo on my van using an adaptation of the BIRA System 1. The bracket is drawn up and the plans are at the machine shop, so its just a matter of time for him to make up the first set. Once I get the brakes installed on the van and insure proper fitment and performance I was going to offer a limited run of these brackets to anyone interested in an attempt to cover some of the initial machining costs.

Off the top of my head I know my bracket will work with the S caliper and I'm pretty sure it'll fit the standard boxster caliper, but not 100%. You'll need to use the brake rotors for a 2000-2002 Audi A8L/S8, and you'll need to turn the stock Vanagon brake rotors down to use as hubs. I also machined down a couple hub centering rings...one to better locate the rotor to the hub, and the other to adapt from the hub to a wheel with a 66.7mm center bore, but these aren't necessary. Still not sure what I'm going to use for brake lines. Haven't gotten that far yet. This system will fit behind most (but not all) 16" wheels.

I ran the numbers in the initial planning stages and discovered that installation of these brakes will cause a large brake bias deficit (surprise surprise) if the stock rear drums are kept, so rear brake upgrades are necessary to keep the van stable under hard braking and fully take advantage of the new brakes' performance. My solution (at least on paper) is the rear rotor from an Audi S5 with a caliper off the rear of an Audi V8 or a 200 with vented rear rotors. This isn't a perfect solution...ideally the rotor needs to be a bit larger, but then I'll run into clearance issues with the 16" wheels I'm running. Any bias issues that may surface can be compensated for with an adjustable bias valve.

Let me know if any of this sounds interesting and I'll keep you posted on the progress.

TTFN,
Adam
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BlackDogVan
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PostPosted: Mon Aug 10, 2009 6:53 am    Post subject: Reply with quote

Hey Dingchowping, what size / source rotors are you planning for the fronts?
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porker buzz
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PostPosted: Mon Aug 10, 2009 12:46 pm    Post subject: Reply with quote

dingchowping are these for early or late vanagon front spindles
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Dingchowping
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PostPosted: Mon Aug 10, 2009 1:05 pm    Post subject: Reply with quote

As mentioned in my first post the rotors are off the front of a 2000-2002 Audi A8L/S8. Its just shy of 13" diameter and will fit behind most 16" wheels when used with the Porsche 993 brake calipers (not 100% sure about the 996 monoblocks, but they're virtually identical dimensionally so they should clear).

I'm putting these brakes on a '90 Multivan, but assuming the wheel offset is the same between early and later models the different rotor offset shouldn't matter, since you'll be cutting off the rotor. The only thing I'm not sure about is the mounting location for the caliper bracket. I'd have to look at an early Vanagon to see how it differs from mine. You may need to swap to later Vanagon uprights for my bracket to work.

TTFN,
Adam
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pete000
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PostPosted: Mon Aug 10, 2009 6:59 pm    Post subject: Reply with quote

Tristar Eric has done it. You need to make adapters and hubs to accommodate the rotors. I have been kicking this around forever. just too much effort for me right now. I have a set of 996 front brakes collecting dust on my work bench.
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Dingchowping
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PostPosted: Mon Aug 10, 2009 7:32 pm    Post subject: Reply with quote

pete000 wrote:
Tristar Eric has done it. You need to make adapters and hubs to accommodate the rotors. I have been kicking this around forever. just too much effort for me right now. I have a set of 996 front brakes collecting dust on my work bench.


No adaptors needed for the rotors after you machine the stock rotors to use as hubs. The adaptors are for the calipers.

The way I understand it Eric used Porsche rotors as well, which necessitate use of Porsche wheels, which have a 5x130 bolt pattern. Also, according to his ad he used 930 brakes. Not the same thing.

When you're ready to install your brakes, give me a shout. I'll have the caliper brackets ready to go unless you WANT to reinvent the wheel. I have the time and facilities to put this kit together, even though I'm sure someone has done this before I wanted to do it on my own. Besides, its only a few modifications to a stock RS2 bracket necessary to get everything to bolt up to a Vanagon.

I assume you're using a spacer that adapts from VW/Audi to Porsche bolt pattern and any brake upgrade you do will add 8mm (the thickness of the rotor) to your wheel offset, or you can go Eric's route. But for those who have existing wheels in a 5x112 bolt pattern, my solution should work well.

TTFN,
Adam
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BlackDogVan
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PostPosted: Tue Aug 11, 2009 2:28 am    Post subject: Reply with quote

Dingchowping wrote:
As mentioned in my first post the rotors are off the front of a 2000-2002 Audi A8L/S8. Its just shy of 13" diameter and will fit behind most 16" wheels when used with the Porsche 993 brake calipers (not 100% sure about the 996 monoblocks, but they're virtually identical dimensionally so they should clear).

I'm putting these brakes on a '90 Multivan, but assuming the wheel offset is the same between early and later models the different rotor offset shouldn't matter, since you'll be cutting off the rotor. The only thing I'm not sure about is the mounting location for the caliper bracket. I'd have to look at an early Vanagon to see how it differs from mine. You may need to swap to later Vanagon uprights for my bracket to work.

TTFN,
Adam


The reason I asked even though you mentioned is 2002 A8's came with 323x30mm rotors & the S8 came with 345x30's so I wasn't sure. Looks like you're going with the small option then. I'd sure like to see a pic of this under a 16" wheel, are you sure it'll fit?
Cool project, post some pics!
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dbo550
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PostPosted: Tue Aug 11, 2009 7:20 am    Post subject: Reply with quote

If i recall correctly at the shop that I used to work at we had better luck with the brakes from the 968. Mostly on jettas and golfs though.
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Dingchowping
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PostPosted: Tue Aug 11, 2009 11:35 am    Post subject: Reply with quote

BlackDogVan wrote:
The reason I asked even though you mentioned is 2002 A8's came with 323x30mm rotors & the S8 came with 345x30's so I wasn't sure. Looks like you're going with the small option then. I'd sure like to see a pic of this under a 16" wheel, are you sure it'll fit?
Cool project, post some pics!


Look closely at my previous post and you'll see I mention using A8L/S8 rotors. Not A8. Standard wheelbase A8s used smaller rotors than the A8l/S8. So yeah, I'm using the bigger rotors.

In my first post I mentioned that this kit is closely based on the BIRA System1. Thousands of these kits have been installed on various Audis and they all fit behind the stock 16" wheels. That's what it was designed for. I don't have any pics handy so you'll have to trust me. They fit. In fact with some wheels (S6 Avus wheels, for instance) no spacer is needed to clear the caliper face.

I'll post pics as soon as I have something worth photographing.

TTFN,
Adam
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Tristar Eric
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PostPosted: Tue Aug 11, 2009 12:40 pm    Post subject: Reply with quote

I made 2 versions,

Version 1 is similar to what you're trying. 930 front rotors mounted to cut down Vanagon rotors, with Boxster S calipers.

Version 2, uses a custom machined hub that slips right onto the Vanagon spindle using Vanagon bearings. The hub has a custom machined hat that accepts a 993 TT rotor. 328mm dia Then I use the famous 993 TT calipers aka "big reds". They mount to the upright using my custom machined caliper adapter.

Version 2 is the ultimate in braking for the Vanagon.

My rears are from an 88 930... using Boxster S calipers as well.

Post some pics!
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Dingchowping
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PostPosted: Tue Aug 11, 2009 1:45 pm    Post subject: Reply with quote

Hi Eric,

Just curious, how's the pedal travel/feel? That's a LOT of pistons you're displacing! I spent a lot of time calculating master cylinder piston displacement vs. stock in an attempt to avoid excessive pedal travel. You're the only one I know running a similar setup...I'd like to know what to expect.

Also, how did you deal with the parking brake? Separate caliper? Or just don't use it? I'm using the V8 rear caliper because I want to keep the parking brake function.

TTFN,
Adam
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Tristar Eric
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PostPosted: Tue Aug 11, 2009 8:18 pm    Post subject: Reply with quote

Pedal is super firm with the stock master cylinder. I also use a Wilwood adjustable brake bias valve. I found the rears to be locking first with the stock bias valve.

I made an internal hub e-brake like the 911's.
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Dingchowping
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PostPosted: Wed Aug 12, 2009 11:29 am    Post subject: Reply with quote

[quote="Tristar Eric"]Pedal is super firm with the stock master cylinder. I also use a Wilwood adjustable brake bias valve. I found the rears to be locking first with the stock bias valve. [quote]

I bet! My calculations show that the stock brake torque bias is about 1.57:1. My guess based on the slightly smaller pistons used on the Boxster calipers vs. Big Reds is your static brake torque bias is somewhere around 1.2 without the bias valve. My system will err in the other direction, increasing bias 1.7:1. I'd like to get that number a bit closer to stock, but that requires bigger rotors (I'm already planning to run the biggest rotors that will fit behind 16" wheels with the V8 calipers), or bigger calipers, which isn't an attractive option for other reasons (cost, added piston displacement, rotor availability/compatibility, etc...).

[quote=]I made an internal hub e-brake like the 911's.[quote]

That is VERY cool Eric! Nice job. That would open a world of possibilities for more ideal caliper choices, assuming you can find a compatible rotor with internal drum. That would allow the Brembo 2 piston caliper used by Subaru for the STI and by Stoptech (the ST20). Thanks for the pics, Eric.

TTFN,
Adam
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a914622
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PostPosted: Wed Aug 12, 2009 11:41 am    Post subject: Reply with quote

[quote="Dingchowping"][quote="Tristar Eric"]Pedal is super firm with the stock master cylinder. I also use a Wilwood adjustable brake bias valve. I found the rears to be locking first with the stock bias valve. [quote]

I bet! My calculations show that the stock brake torque bias is about 1.57:1. My guess based on the slightly smaller pistons used on the Boxster calipers vs. Big Reds is your static brake torque bias is somewhere around 1.2 without the bias valve. My system will err in the other direction, increasing bias 1.7:1. I'd like to get that number a bit closer to stock, but that requires bigger rotors (I'm already planning to run the biggest rotors that will fit behind 16" wheels with the V8 calipers), or bigger calipers, which isn't an attractive option for other reasons (cost, added piston displacement, rotor availability/compatibility, etc...).

[quote=]I made an internal hub e-brake like the 911's.
Quote:


That is VERY cool Eric! Nice job. That would open a world of possibilities for more ideal caliper choices, assuming you can find a compatible rotor with internal drum. That would allow the Brembo 2 piston caliper used by Subaru for the STI and by Stoptech (the ST20). Thanks for the pics, Eric.

TTFN,
Adam


Adam
So just for grins, plug the Lexus LS400 1996 front calipers and rotors in your system. Is that closer to the stock bias???

jeff l
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Dingchowping
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PostPosted: Wed Aug 12, 2009 1:16 pm    Post subject: Reply with quote

Hi Jeff,

Are you talking about using the Toyota brakes for the front or rear? Do you have the specs handy? Rotor diameter, offset, bolt pattern, center bore, and caliper piston diameter/count? Is the caliper a floating style? I assume it is, in which case its a moot point.

TTFN,
Adam
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PostPosted: Wed Aug 12, 2009 3:20 pm    Post subject: Reply with quote

Toyota 4 pot fronts from a 96 solid like the brembos/ 996 porsche . rotors are 12.4 dia. and 1.26 thick. I think the pistons are staggered size. 20mm front 19 mm back but im not sure of that. The rotors are almost the same as the Syncro offset and one of the 2 bolts on the caliper is almost the same as the vanagon. Rears are floating audis.

I was just think if you had a program that spit out the bias, it would be interesting to see what im running..

thanks jeff
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PostPosted: Wed Aug 12, 2009 4:01 pm    Post subject: Reply with quote

a914622 wrote:
Toyota 4 pot fronts from a 96 solid like the brembos/ 996 porsche . rotors are 12.4 dia. and 1.26 thick. I think the pistons are staggered size. 20mm front 19 mm back but im not sure of that. The rotors are almost the same as the Syncro offset and one of the 2 bolts on the caliper is almost the same as the vanagon. Rears are floating audis.

I was just think if you had a program that spit out the bias, it would be interesting to see what im running..

thanks jeff


You might want to confirm those piston diameter numbers. I don't have a program, just do the math by hand. I can't find all my paperwork at the moment, but I know that the Big Reds with their 36mm and 44mm diameter pistons are actually a close match to the stock caliper's large single piston. If the Toyota caliper does in fact use 19 and 20 mm pistons they'd produce considerably less torque than the stock caliper and you'd need a huge rotor to compensate. I also need to know the pad coefficient of friction, but those numbers are VERY hard to come by.

I'm interested in your rear caliper bracket. What rotor do you use?

TTFN,
Adam
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pete000
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PostPosted: Thu Aug 13, 2009 1:50 pm    Post subject: Reply with quote

Here is an old picture I had of Erics Boxster set up.

Hey Eric I just noticed the bleeders are pointing down, whats up with that...

And is that a prototype H & R Cup spring on there? Interesting bend. I didn't notice that before either.

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PostPosted: Thu Aug 13, 2009 3:28 pm    Post subject: Reply with quote

I'm not Eric but there's two bleeders, one up one down, so the caliper can be used universally on the left of right side of the van/car
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