More cost effective Brake upgrades ??
 

Now that I've sorted out most of the other issues, I'm exploring upgrade options for the braking.....

Besides the usual upgrade to the "S" front brakes and or aftermarket pads, are there other cost effective brake upgrades.

The "S" front brakes seems to be only marginally bigger so are they really worth upgrading to ??

I'm looking for upgrades such as using brakes from the cayenne or 911 ?? I'm exploring the Cayenne brakes as there is a set for sale coming off a 2011 Cayenne S which someone is taking delivery of, next month. Unfortunately I don't know whether the calipers and rotors will fit - firstly because I'm still on 17" rims and whether the caliper mounts will fit (plus offset ??) ??

Are there calipers/rotors from the other Porsche models that are known to fit with minimal modifications ??

The car is used more for high speed highway driving, not track. Am looking for alittle more confidence in the braking power, which is currently marginally sufficient when you are dodging a truck that just suddenly pulled out in front of you (unfortunately that's the way the drive here) on the highway. I used to have 345mm front and 312mm back on my VW Scirocco and that had oodles of braking power to spare..

The primary advantage of larger brakes for the Boxster is greater cooling and the ability to avoid brake fade during repeated heavy braking.

My first suggestion for better brake feel is a set of stainless brake hoses and a good flush with Ate Blue.
Beyond that, you'd want to go to a different set of brake pads. How much noise & brake dust are you willing to put up with?

I've already got the stainless brake hoses. Not sure what brake fluid I've got though...

Rather have less brake dust and noise, but if it helps... Current rotors are zimmermans and the pads are textar (standard items...).

Any suggestions for pads ? Something with not too much noise, hopefully.

S front brake upgrade is worth it, been done many times by many people. Nowadays I have to watch who's behind me when I hit the brakes hard. :cool:

If you want even better brakes, get the Girodisc rotors which are even bigger than stock S brakes but requires at least 18-19" wheels to fit.

If you want even better brakes, get the 6 pistons Brembo GT kit which is around $5000USD.

the cayenne brakes are huge and heavy, designed to stop a VERY large vehicle.

the S brakes are a HUGE upgrade to the boxster; no comparison on the track. i had many problems with the standard brakes & never really had confidence in the system. the S brakes + GT3 brake ducts bought + race pads bought me almost two seconds a lap & instill a lot of confidence by comparison.

IMO, you will see a net performance DECREASE w/ cayenne brakes due to increased unsprung mass. i bet you'll get better stopping distance w/ the S brakes.

after a point, it all comes down to tires anyway......

Cayenne brakes are popular mod for Audi TT and Golfs... but I agree you can only have so much brakes until you reach the limited grip of the tires.

Insite is right on the money.
That said, if you don't track the car, I would keep your calipers. Then put in fresh fluid and good pads. After that, tires will dictate how quickly you stop.
Going to anything else will be wasted money and potentially decreased performance based on where you drive.
Oh, and frequently pads that throw off a lot of dust are the ones that stop best. It's up to you to determine where you fall on the scale of
No Dust ------------ Stopping Power

Put the GT3 ducts on. I do track my car, and noticed a great deal less fade on extended runs after installing the ducts. Now I don't have the guts to push the car as deep as the brakes will allow. Best (or maybe only) useful cheap/easy mod you can do!

Has anyone had experience with these?

http://cgi.ebay.ca/NEW-GENUINE-PORSCHE-986-BOXSTER-BIG-RED-BRAKE-CALIPERS-/360341926385?pt=Motors_Car_Truck_Parts_Accessories &hash=item53e60d71f1

Any thoughts?

:cheers:

I don't see why, given your driving situation, you need to upgrade the brakes. The stock brakes have more than sufficient power to stop your car very quickly, at Autobahn speeds. What bigger brakes are going to give you is additional fade resistance. But for highway driving, you won't need that. For highway driving, your biggest differentiator is the tire. On track, it's a completely different story of course...

Remember that stopping distance is mostly a factor of weight and tire grip, not brake components. Base Boxster brakes are some of the best in the business with a stopping distance similar to a Ferrari Marinello. If your car does not stop on a dime, there is something terribly wrong with your brakes (contaminated brake fluid, bad master cylinder, bad wheel caliper. bad brake booster, etc.)

Get your brakes checked by a qualified tech. After having your brake system thoroughly serviced, switching to a more aggressive bite will give you quicker braking response with less pedal effort. Pagid black, Performance friction 03, Raybestos ST-43 are a few good choices with a lot of bite. These pads will easily overpower a set of stock street tires on the front. Maybe just better tires is your answer.

topless is right. the difference w/ the brake upgrades is not the stopping distance. it's how many times in rapid succession you can panic stop without boiling the fluid, fading the pads or causing a fire.......

with cars like the cayenne, even a single panic stop from 100mph could cause fade problems if it had the brakes of, oh, a boxster...... weight is a concern.

with a tiny car like the box & only street driving, you will, as i said, see a net performance LOSS due to the added unsprung weight if you put cayenne brakes on your car. now if you want them because they look cool, well that's a different issue. :)

I seem to remember someone saying that when you put Box 'S'/996 front brakes on you can take your 'old' front calipers and rotors and put them on the rear. (Front left to right rear, Front right to left rear) Any truth to this?

Hmmm, thanks for all the inputs.

I've currently got pretty new Michelin PS3 upfront and PS2 behind (both less than 8k km).... Made the mistake of changing the front to PS3 then realized that they don't make PS3 of the right size for the rears. The fronts are not N specs. But I presume this shouldn't be the cause of my problem ?

Oh, my front calipers were rebuilt afew months ago (one side sticking).

Does the ABS system on the Box come on to prevent ALL wheel locks ?? I did lock my front wheels once or twice and the ABS didn't come on.. No ABS warning light on at the moment. I've never felt the ABS coming on before at all (I presume there would be juddering feeling from the brake pedal ?).

Maybe I need to have that looked at first. Maybe a faulty ABS sensor ??

Quote:

Originally Posted by Roy_Josef I seem to remember someone saying that when you put Box 'S'/996 front brakes on you can take your 'old' front calipers and rotors and put them on the rear. (Front left to right rear, Front right to left rear) Any truth to this?

you CAN do this, but DON'T! the brake system is designed to have smaller caliper pistons in back than up front. the pistons on the boxster front are the same size as the boxster s front. this means that by putting the front calipers on the back, you change the brake bias.....a lot.

since the car dives when you brake, roughly 70% of the car's weight is over the front tires during a heavy stop. this means that about 70% of the car's braking power is designed into the front brake system. if the rear brakes are too big, the rears will lock up well before the fronts (particularly if braking in corners). the potential for spins is very real. just ask pedro. :rolleyes:

Well first of all that's called trail braking. As a novice you're not supposed to have your foot on the brake when you enter the corner anyway. It's an advanced driving technique and definitely not for someone who's not experienced.

That being said, I'm going to do the swap, but don't to what I do. It's bad for you. :D

it's not called trail braking on the street. how about a panic stop in wet weather on a slight bend? the bias is too heavily rear for street OR track. if you do this, it's not a matter of if, but WHEN you will spin (street or track). a brake system is supposed to be balanced. moving the fronts to the back is a dumb idea.

Shlim8,

Sounds like you indeed have brake issues. Take your car out to a barren road and do a few full simulated panic stops from 50-0. Your car should go into ABS judder every time with no wheel lock up. If it does not you need some brake work. My car is really set up for track rubber and I get used to threshold braking and very high braking forces. When driving on the street with stock 205mm PS2 tires I get into ABS a lot.

I had a brake situation similar to the OP when I first bought my used Boxster - I'd slam on the brakes at about 50mph and it seemed like the car just didn't want to stop and the ABS wouldn't kick in. I also tried pad break-in runs with no improvement.

I also replaced the tires with Michelin PS2's. Whether PS2 or PS3, the tires should now be fine and giving you all of the grip needed to stop very well.

I decided to start at the obvious and work my way up so the first thing do to was to replace the rotors and pads (I went with Cquence drilled rotors and EBC Redstuff pads but any good rotor and pad would be fine for the street). I also installed the GT-3 brake ducts at the same time (cheap and easy). Didn't touch the fluid or ABS system.

Now I can stop on a dime and as another writer commented, I have to be careful about out-braking the car behind me on the street and worry about getting rear-ended. Also, now if I get on the brakes hard, I can get the ABS to engage and feel the judder.

If this hadn't addressed the issue, then a full brake fluid flush would have been next.

If pads, rotors, and fluid hadn't worked, I'd have taken the car in to a mechanic or dealer for evaluation and see what they recommended.

thstone, before u did all the mods on your brakes.... did your brakes lock but the abs didn't kick in ? Or the car just refused to stop but brakes didn't lock ? In my case, I think the brakes are working well but the abs has yet to cut in. It does take pretty hard braking to lock the brakes.

Some people confuse initial "bite" or "grab" with ultimate stopping power because it is very noticeable. The easiest way to increase "bite" on a road car is to increase cold pad friction and rotor diameter. Although it is entertaining (and somewhat reassuring) in dry conditions, too much "bite" can actually be a safety hazard in wet or slick conditions. It is actually more important to have a system with a fairly wide modulation window, rather than on/off like a light switch.

To complicate matters, many race pads have to be warmed up to get to their optimal stopping power, through repeated braking cycles, something that is less frequent in street driving. Some of the best enduro race pads have very low friction in the first application out of the garage (or driveway).

Any good "sport" pad will help a lot on the street, but it will probably be slightly noisier and dustier. Oh well. Also make sure your fluid is properly bled and that the rotors have NO grease on them. If you still have a problem, you might still have a sticky piston.

All the modern Porsches already come with great brakes that have been fade tested well beyond most other car manufacturers (as well as suspensions that are capable of more cornering speed than you could ever safely use on public roads). All the Boxster brakes are made by Brembo, and there are actually VW and Audi guys (and some older Porsche owners) waiting for you to take the brakes off of your car so that they can put it on their cars.

For the street, focus on getting great tires and great pads, and the rest is tweaking.

p.s. As far as putting base model front calipers on the rear, you should listen to insite, as he is a pretty smart guy. It did not occur to me that both the base model and the S use the same brake piston diameters (fronts 40/36mm, rears 30/28mm), so I checked, and he's right. Unless you have a way to adjust brake bias (and most street cars don't), putting the same size pistons front and rear will cause massive rear wheel lock-up (or massive puttering, with ABS). Not fast, either on the street or the track...

How about a brake bias valve off another car? We used to do this (a lot!) right or wrong back in the day for both the 914 and the 944.

For the Boxster S front brake conversion - do I just need the S calipers + rotors or do I need something else ??

Quote:

Originally Posted by Roy_Josef How about a brake bias valve off another car? We used to do this (a lot!) right or wrong back in the day for both the 914 and the 944.

this is actually okay. rather than use one from another car, you can replace the proportioning valve with an adjustable one. they allow 'full force' to the fronts & let you limit pressure to the rear until appropriate bias is achieved.

just be sure you know what you're doing first. rear-bias settings that seem fine in a straight line on dry pavement may be to aggressive for wet weather & curves.

Thanks, good to know! I have all the bits necessary to do this and was thinking of doing it when I have everything apart to install my coil overs when warmer weather finally arrives. Any suggestions on a 'perfect fit' bias valve? I remember when we did 'Medium Red' brakes from the 944 Turbo 'S' on the regular 944 we would use the 928 S4 bias valve and when we did did the BMW 320i front brakes on the 914 we would completely take out the factory bias valve and install a VW 'Tee' bias valve fitting instead. Does nothing with a Porsche part number on it work?

roy -

you'd have to scale the pressure back proportionally to the area of the total piston size for the calipers.


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the fronts, if you put them on the back, will now have 40mm leading pistons and 36mm trailing pistons. the OEM rears have 30mm leading pistons & 28mm trailing. the difference in disk diameter is only 6mm and negligeble.

so, the new rears would have total area of 9100 square mm (remember, two of each piston per caliper) and the old rears would be 5300 square mm.

now let's consider the OLD system. the fronts were 9100, the rears were 5300 and the OEM proportioning valve has a .46 reduction factor. if we multiply the 5300 by .54, we get 2860 sq mm equivalent area from the rears.

back of the envelope to check our work: roughly 75% of the braking is done by the front. what is 9100/(9100+2860)? it's about 76%, so we are spot on.

now let's calculate the reduction factor required to give us the same proportion as OEM, front to rear.

our NEW boxster S calipers have, believe it or not, the SAME piston sizes as the base boxster. the disks are 20mm bigger, though, so first we need to calculate the EQUIVALENT area at the OLD disk diameter. let's assume that the center of the brake pad works on roughly the outer 40mm of the disk. this means that the OLD lever arm is 109 mm and the NEW lever arm is 119mm. the increase in braking torque is then 10/109 = 9% with equivalent piston sizes & system pressure.

so now we increase our 9100 by 9% to get the EQUIVALENT piston area in terms of the old system: 9920.

so what proportioning valve reduction will get us from 9920. to keep the same bias as before, we need our rears to be reduced to (9920 / .74)*.26 = 3485.

we need to reduce our new 9100 sq mm effective rear piston size to 3485. this is a reduction of 5615, or .62.

BTW, proportioning valves keep the F/R bias at 1.0 (NO reduction to rear force) until some pre-set pressure value. porsche's factory valve begins biasing at 25bar / 360PSI.
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END ENGINEER SPEAK


you want: proportioning valve w/ a reduction factor of .62 and a divergence pressure of 25bar.

or an adjustable valve like this one:

http://www.amazon.com/Wilwood-260-8419-Adjustable-Proportioning-Valve/dp/tech-data/B002G37IEA

take care.

Awesome explanation! I had to read it a couple of times but it makes sense. Do you teach this stuff, because you do it well...

I was hoping for a Porsche bolt in solution to get away from re-plumbing/bending the brake lines to use this aftermarket solution or is it less complicated than it seems?

glad you enjoyed it. :-)

the bottom line is this: there is no real reason to upgrade the rears. upgrade the fronts & be done with it. if you track the car, play with different compounds front to rear & find a bias you like.

if you do change the proportioning valve, it's in the driver's side fender. not too tough. plumbing an adjustable proportioning valve isn't that tough, either, but it does take some special tools.

Had my abs checked out last week. It is working but it doesn't kill all of the brake lock, but it does make the car controllable. According to my mechanic, it's to "optimize" braking without losing control of the direction of the car.

Is this normal ?? Or is my mechanic explaining away a problem ? I still get loud screeching noise from the tires (lock), but car direction is controllable. Locks pretty easily but it does stop on time.

WIll it help if I use wider tires upfront (lock is from the front) - I am still on the standard 205 upfront (PS3) and 255 rear tires (PS2). WOuld seem logical since the rears are so much wider but then isn't the brake pressure proportioning valve supposed to help on this ? These are standard 986 17" tire sizes.

Anyone have the same issue ? Or is there something wrong with my car ?

shlim8 -

the charictaristic function of boxster ABS is pulsation. when the ABS kicks in, you will feel the car pulse the brakes a couple times a second. this is very obvious through the pedal. if the tires lock up and stay locked up for more than a split second, your ABS is not working properly.