2008 SP STi brakes

Hey all, I've been doing a lot of work on our SP car at work because it had been a little neglected and needed it and because I agreed to co-drive in it.

The car is a pretty straight forward build: 2008 STi with the required safety stuff, underbody protection, a few reinforcements to suspension components, RS&SP with hyd bump stops and brakes downsized to Subaru 4/pot 2/pot with braided lines, Motul RBF600 fluid, Ferrodo DS2500 pads and front two piece rotors from racing brake also stock master, booster and even ABS so the stock center diff controller still works.

Here it is:


The car is heavy at 3350 lbs but that's minimum weight for the class after we upgrade to the forged pistons to increase service life.

The car seems to be really hard on the brakes, the looks on the workers faces when we roll up to the finish control tell me that none of the other cars brakes are on fire.

John and I have been talking about a kit for subaru's using a wilwood forged superlite for a while and now they have a new radial mount one out and the price and weight is almost half what the Subaru 4/pots are, the pads and rotors are cheaper, thicker and come in more varieties. It's basically the setup that Chris Martin is running on his GC open class car but with Willwood components rather than AP Racing.

I know this would be a good setup for a 2700lb open lite Subaru but is it going to be enough to stop our 3400lb pig and what rear caliper should I use? Is this caliper even close to as good as the AP Racing CP8350, what makes the AP one better? All the cars at the top of the class have the group N brakes but it seems like your just paying way too much for Homologated parts when we can run whatever we want as long as it's a maximum of 4-pistons per front wheel and 2-piston per rear.

I also want to add a hydraulic handbrake and keep the factory 4-channel abs (so the diff controller still works) and it seems like my options are the ubber expensive Group n 4-port ones or a setup that uses two of the girling style masters. Are there any other options, can I use a 4-port master from a street car, like a 93 ford t-bird

Welcome to SP.
CP6800 series from AP is where I'd start to look.

Stock 4/2 setup will be rotors/pads per event and likely caliper per event or two.

Wilwood may not be much of an upgrade over the stock setup and will probably cost you more in the long run if the caliper life is significantly shorter.

Put aside $5k for the upgrade or just plan on replacing all the components often. Ducting to help cool might be good also. Stop braking so much.

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Grant Hughes

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NoCoast
Stop braking so much.

Less braking, less breaking

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johnhuebbe

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NoCoast
Stop braking so much.

Less braking, less breaking

I never use the brakes at all, I just say right or left

You dont have to stick to a 2 piston caliper in the rear. My STI is an SP car and has the GrN brakes, and thats a 4pot from and 4 pot rear. Also, The center diff can work with just the ABS controller, you dont need to keep the pump and the lines setup diagonally.

As for what brakes to run, dont run the wildwoods, its asking for trouble, and think about it, if you already set your brakes on fire, why would you want something lighter and flimsier. No the willywood calipers are nowhere as good as the 8350 AP. They flex too much and the machining is horrendous. The internals are so rough that some calipers never bleed properly because air gets trapped in there.

That being said, I have the designs and intentions to make a kit for the STI's using the AP caliper, I just havent had enough people jump on the bandwagon to amortize the machining costs.

Every time i drive the car with the AP front brakes (stil using Subaru 2 pot rears) it puts a smile on my face. Probably one of the best things i've put on the car, regardless of cost.

I wouldn't be so stuck on the stock DCCD unit. You can get many good diff controllers for around $500.

On a somewhat related note, I cannot for the life of me believe how crazy the SP cars have gotten! Full motec systems, everyone on ExeTC suspensions, full Group N brakes!

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Chris

You might be able to find something here that could just use a rebuild. The ex-NASCAR stuff can be had for real cheap if you don't mind buying used.

ebay.com/search is easy/ nascar brakes/lmgtfy#rolo#yolo#illseemyselfoutnow

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Robert Culbertson
You might be able to find something here that could just use a rebuild. The ex-NASCAR stuff can be had for real cheap if you don't mind buying used.

ebay.com/search is easy/ nascar brakes/lmgtfy#rolo#yolo#illseemyselfoutnow

Nascar piston sizes are always too big..4 x 1.75 is too big. 2 x 1.75 and 2 x 1.875 is way too big...
And if you fuck around with master sizing such that you get a decent feel on the pedal, they will be so goddam touchy that there's too much conciousness to modulation needed. They'll be too touchy.

As a guide just look at the sizes Subie and Misterbitchi used on their "under 15" wheels' set ups.

Since that';s easier than believing somebody who has posted sized for a slew of works cars dozens of times.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

NASCAR brake calipers are too wide for rally. They are made for a minimum of 32mm disc and the smaller calipers takes 25mm thick pads. Even the late model calipers are a tight fit around the spokes and only take a 20mm pad.

Yo John, read the listings maybe huh? A lot to be had in the 1-1.25 range mate.

I didn't even think about the width, though that's definitely something to consider. I know that most (all) would require some custom hats with some serious offset. Can you machine the halves down and narrow them up, assuming non-mono-block caliper?

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Robert Culbertson
Yo John, read the listings maybe huh? A lot to be had in the 1-1.25 range mate.

I didn't even think about the width, though that's definitely something to consider. I know that most (all) would require some custom hats with some serious offset. Can you machine the halves down and narrow them up, assuming non-mono-block caliper?

And just what do you intend on doing with caliper with pistons ranging from 1.0 to 1.25" range?
I know what I've seen and i know what I've made and supplied and that's a rear caliper with a pad about 100mm long for a car around 2500-2900 lbs..

That's not the problem...

Read the sizes i said to looking for maybe, huh?
http://www.apracing.com/products/race_car/brake_calipers/rally_range.aspx

Hasn't changed a lot since the old days
http://www.apracing.com/products/race_car/brake_calipers/historic_range.aspx

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

John, I have absolutely no idea how to size brakes. I've never tried. I just make changes based off the current setup and I'm almost always happy with the changes. I wasn't even suggesting that those were the sizes I would run. I was just saying that there is a RANGE of parts available. That is all.

Thanks for the links though. That's some good info.

So are you saying that 1.5-1.625 is the "right size".



Edited 1 time(s). Last edit at 05/10/2014 06:41PM by Robert Culbertson.

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Robert Culbertson
So are you saying that 1.5-1.625 is the "right size".

No. There's no right size, WTF is this idea now that caliper pistons NEED to be a certain size because [enter fucked up idea]?!?!?!

If the caliper pistons are bigger, then match with a bigger master cylinder for the appropriate clamp load. SIMPLE... that's it.

And as a matter of fact, bigger pistons are preferable because the system requires less pressure, so less line expansion in the flex hoses, less pressure on the seal, etc, and with the masters being bigger it provides and extra "cushion" of volume, so when the brakes start to over heat you wont lose a pedal as quick. These are some of the considerations for development on brake setups on real race cars, not some predefined idea that it has to be xxx.xx


That being said, the average size of a NASCAR caliper piston is 41mm/44mm for short tracks, and ~36mm/41mm for intermediate tracks. Now to give a rally example, the homologated GrN Brembo calipers for the Evo come with 38mm/44mm piston arrangement.

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Cosworth

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Robert Culbertson
So are you saying that 1.5-1.625 is the "right size".

No. There's no right size, WTF is this idea now that caliper pistons NEED to be a certain size because [enter fucked up idea]?!?!?!

If the caliper pistons are bigger, then match with a bigger master cylinder for the appropriate clamp load. SIMPLE... that's it.

And as a matter of fact, bigger pistons are preferable because the system requires less pressure, so less line expansion in the flex hoses, less pressure on the seal, etc, and with the masters being bigger it provides and extra "cushion" of volume, so when the brakes start to over heat you wont lose a pedal as quick. These are some of the considerations for development on brake setups on real race cars, not some predefined idea that it has to be xxx.xx


That being said, the average size of a NASCAR caliper piston is 41mm/44mm for short tracks, and ~36mm/41mm for intermediate tracks. Now to give a rally example, the homologated GrN Brembo calipers for the Evo come with 38mm/44mm piston arrangement.

Where dopes the idea come from? PRAXIS---latin for "previous practice.
Who knows--- maybe it is just pure coincidence, a random freal of nature but actual measurement and double check with AP part numbers and I have seen over 3 decades of top level rally cars very consistently having front caliopers with 4 x 1.5" when they weighed about 2000-2250 lbs
Ford Escort Group 4........
Saab 99T Group 4

Later GrA cars 1150-1250kg
Fronts either 2x 1.5" + 2 x1.625"
or occasionally on very fast events 4x 1.625"

Ford Sierra Coswoth 2wd, 4WD and Escort Cosworth as well as World Rally Car
VW Golf
Opel Kadett E GSI
Volvo 240T
Misterbitchi Gaylant
Subaru Le-gassy

And asked pointedly: Subaru Impreza

Later Group N cars whn they got round to loading up GpN cars with the right parts
Subaru Impreza
MisterBitchi Lancer Evo

It must be the most amazing coincidence but all these different cars I have measured and check PNs...

Paulino you have decades experience... But sometimes i will belive what I have seen and measured and when I see it is consistent to size of car(weight) and speed and surface---all these are GRAVEL cars in ther best gravel countries in the world by far....

Then I will believe THAT...


Just look at the consistency of circle track sizes......very narrow selection...

Again just happened to be what they found laying on the shelf...or does weight-speed-surface have something to do with getting the power and a "good pedal"--good modulation...???

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.