Questions re:S2 to Turbo brake upgrade

[Joss Walker]

Hi All

I have been test driving a couple of new cars recently and am now slightly terrified of just how poor my old S2 brakes are. I have known for some time now that I need to refurbish them but am thinking of trying to upgrade to Big reds (which are tricky to track down at a reasonable cost) This would also allow me time to refurb these whilst off the car.

Are the 944 four pot Turbo brakes (from a 1991 car) the same as the fabled 'big red'? I assume these would be a big step up from my standard S2 calipers, do I also need bigger discs? if I replace both front and rear do I need to do anything with the bias valve? and finally, will they clear my wheels? currently I am running on some of the boxster five spoke jobs (courtesy of PO) that you see on loads of 944's, as shown on my avatar.

Any advice, as ever, will be appreciated

Joss

 

[sawood12]

The later 944 turbo brakes are not quite as large as big reds/big blacks but have the same piston diameter so can provide the same hydraulic force. The big blacks are physically larger and the brake pads are about 30% bigger. Larger brake pads allow you to generate the same braking force at lower temperatures. Late 944 turbo brakes will fit under 16" rims but big reds/big blacks will need at least 17" rims as the disks are significantly larger diameter and thicker again.

For S2 to late turbo upgrade you will ideally need the hubs off a later 944 turbo, but since these are rare as hens teeth you can get adaptors. You'll need the bigger discs (marginally larger in diameter but thicker).

Once you've upgraded to late 944 turbo brakes then big reds/big blacks are a direct bolt-off / bolt on replacement, maybe apart from the disc backing plate which you will probably have to remove when fitting big reds/big blacks.

Just to confirm - big reds were fitted to the 993TT, big blacks were fitted to the 928GTS and 964 turbos. The callipers are identical apart from colour and the big reds fitted upside down relative to big blacks (installed in front of the hub rather than behind it). So for big reds you need to modify them to install on a 944 (just swap around the U-pipe with the bleed nipples), but big blacks will bolt right onto the adaptor or later 944 turbo hubs.

For discs, you can't use 993TT disks on a 944 as the 'top hat' is a different offset, however you can use 928GTS discs if you want solid, or 964 turbo disks if you want drilled (only good for aesthetics - don't be fooled about the claims of better braking performance, water displacement, venting of gases etc. They are more trouble than they're worth with cracking holes, holes that block up with brake dust, not to mention greater expense. Having said that, aesthetics is as good a reason as any to go for them - but you'll need 968 MO30 rear disks to get drilled rears and they are big bucks)

993TT discs were two piece disks so the brake disc could unbolt from the central top-hat. You can buy these separately and Lindsay Racing do a nice CNC machined and anodised central top hat which you can bolt the 993TT disc onto which bolts upto the 944.

 

[edh]

The brakes on later 944 Turbos are sometimes called "reasonably big blacks"

Might be even cheaper to buy some more S2 calipers & get them reconditioned. I'm sure when working "as new" they will be great.

 

[Joss Walker]

ORIGINAL: edh

Might be even cheaper to buy some more S2 calipers & get them reconditioned. I'm sure when working "as new" they will be great.

This was my original plan, my car is a weekend driver only so the service that RPM offer is ideal, however I wasn't sure how good the reconditioned S2's would be, I realise that I can't expect them to be up to the standard of modern brakes so that is why my eye was drawn to an upgrade.

Scott - thanks for your very comprehensive response. the setup I am considering is from a breakers yard on ebay:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=260758483228&ssPageName=STRK:MEWAX:IT
and they have advertised them as big reds but from your information I don't think that they are, (of course this means that I may be able to get the rear hubs as well) would this setup be a big improvement from the standard S2? I would imagine so since they were fitted to the faster turbo and I'm not convinced that this was just a marketing ploy. Your reference to the greater hydraulic force sounds very tempting. I would probably want new discs as well so this all starts to become expensive and I'm concerned that this whole enterprise is based on my whim with no evidence/experience!

Has anyone had experience of driving an S2 and a Turbo, with good brakes?

 

[robwright]

The brakes on my 88 turbo are pretty god damn good even with their plate lift. I am currently in the process of refurbing all four calipers (plate lift, de-clag and nice shiny red paint). By the time I am finished and refit them I expect them to be stonking and well on par with modern day performance brakes.

 

[chrisg]

Joss

the difference in the size and nomenclature of the brakes has already been covered so I won't repeat this. I would strongly follow Ed's comments.

Fact, Porsche never under engineer the brakes on their cars, particularly those equipped with the 4 Pot Brembo calipers.

I ran an S2 for track days for several years - never had problems with the brakes. I suspect you problems lie not with the setup but the state or deteriation of the brakes over the 20 or so years.

I would recommend the following:

1. Caliper plate refurb all round

2. New Pads and discs (certainly at the front if not x 4)

3. Braided hoses all round ( actually cheaper than the Porsche rubber hoses)

4. Decent DOT 4 fluid

5. Inspection and where necessary replacement of any of the hard pipes

Having done all of the above, I think you'll be very impressed with your original set-up.

If you start adding in larger Turbo or 993 front brakes you could run into issues with fluid volume, compatbility with Master Cylinder and or rear brake bias......

Trust me, you're S2 brakes (when in good condition) are plenty good enough even for very spirited driving and sticky tyres

Yours

Chris

 

[bmnelsc]

I'm with chrisg on this one. The S2 brakes are plenty - especially for a weekend driver.
In my experience, hard piston seals in the calipers are the cause for poor braking - and they often don't leak so no symptoms other than needing both feet and a friend to generate substantial braking force. On one of my old runners - I almost put myself through the windscreen after changing calipers - I was giving it that much leg just for normal driving....

On the subject of turbo or 928 brakes - the rotors are only slightly larger in circumference than S2 rotors. I would assume increased thickness would improve heat management but for non-track use I really can't see that much improvement over the S2 setup.

And finally - S2 components must be top gear as anything for an S2 seems to cost as much or more than the corresponding bits for any other 944

 

[zcacogp]

ORIGINAL: chrisg
Trust me, you're S2 brakes (when in good condition) are plenty good enough even for very spirited driving and sticky tyres

This guy may look funny* but he is always spot on with his comments about 944's. If your S2 brakes are lacking in performance it's 'cos they are not in good nick. Do all that Chris has suggested in his post above and your car will stop like you have hit a cliff face. S2 brakes (in good condition) are more than powerful enough for the car, and being proper brakes with big 4-pot calipers and small servos they offer really good, progressive pedal feel and huge bite when you push them hard. (Do note however that they can be heavy when compared to modern cars - this is to be expected.)

If your car is a weekend driver only then you are in an ideal position to refurbish (or have refurbished) your calipers and refresh everything else. And even the most expensive caliper refurb will be cheap in comparison to a set of Big Blacks. Check for plate lift (and remove any that is present - there has been a thread on this on here recently), put some fresh new pads in and change the fluid and you will be amazed at the improvement. New disks will be necessary if the old ones are worn, and new pipes will be the icing on the cake.


Oli.

* - Sorry Chris; I know that was a bit mean but I couldn't help it! []

 

[sawood12]

the brakes in the ebay advert appear to be off a late 944 turbo (so medium blacks) but painted red. the problem with buying used brakes like these is that they are probably in as poor if not poorer condition than your current ones - they almost certainly will be suffering from plate lift. The standard S2/early turbo brakes are more than man enough for the vast majority of drivers. All bigger brakes gives you is better heat management (actual braking capability is limited by grip from tyres and not brakes), so if you do alot of track work then overheating may be an issue. Downsides of bigger brakes is unsprung weight. Though there wasn't a huge difference in weight between my early turbo calipers (same as S2) and the big blacks I got, the disks were significantly heavier.

Unless you want the aesthetics of bigger brakes then you're much better off refurbing your current brakes - they will be perfectly adequate. I got my big blacks in an upgrade kit from the states back in the day when you got $2 to the £, so it was actually marginally cheaper to get the kit compared with refurbing my old calipers and getting new discs and pads.

 

[Lowtimer]

Don't forget that even disregarding the money, bigger brakes are not "free" - there are disadvantages as well as advantages. Bigger calipers and discs mean more unsprung weight, and brakes which need 17" wheels to fit will cause a further increase in unsprung weight through the bigger wheels. (Also I think the cars are nicer to drive on 16" wheels than 17".) If you increase the size of the calipers they will need more volume of fluid to work, so you will have a longer pedal.

For any sort of public road use the late Turbo brakes are well up to a 300 hp car driven hard, and the S2 brakes well up to anything an S2 can throw at them. It sounds as if you will have the sort of transformation you are looking for simply from a thorough refurb and renewal of your S2 system to the original spec.

 

[Copperman05]

I would keep the originals, unless your doing alot of track days you really wont need an upgrade.

Edd

 

[chrisg]

Thanks to my learned colleague Oli for his vague compliment.....

Another thought regarding the brakes and 'feel' rather than efficiency, don't forget you're using a Master cylinder that's 20+ yrs old and more importantly, the feel will never be the same as a modern car as the UK 944's are a compromised LHD version = connecting bar from the pedal to Master Cylinder.

Modern RHD cars have 'proper' full conversions - no matter how good the Porsche set up there's no substitute for a direct connection to the Master Cylinder.

Oh and another thought, the ABS systems on our Porsches are by today's standard very crude and clunky (albeit they certainly do the job...).

So, I guess what I'm trying to say is the brake system on you 20+ yr old Porsche can be refurbed and made very efficient but it will never 'feel' as sharp and tight as say a current Passat, BMW etc.

Chris

 

[Indi9xx]

I would generally agree with the posts here, especially the fact that tired hydraulics, calipers, disks and pads can make a massive difference to the brakes on our cars, a well sorted 944S2 or 86 turbo will out brake a similar car with even tired big blacks, hydraulics and 964 turbo disks.

To be honest, I have experienced MO40 944 Turbo's in need of attention which the customer thought was fine, but could have been beaten in a stopping distance contest by our ford courier vans with single pot calipers and drums on the rear! However the same car, when overhauled, will outbrake nearly every car on the road, with the exception of exotic new hardware.

But we do need to be clear on one thing, simple physics.

Bigger disks are not just for show.

Thicker disks provide more heat sink and are less likely to fade.. not so important day to day, more important on the track, but also even on a hard drive on twisty country lanes. The larger mass or thicker disks have a capacity to store much more heat during brake use, and the increase in disk thickness and therefore surface area increase the disks ability to dispose of heat between braking events.

Larger diameter rotors increase braking force, even with the same size caliper. You could imagine the disk diameter increase a little like increased leverage, but in effect its torque, which is calculated as Torque = Force x Distance. So the further from the disk centre that force is applied, the greater the torque applied. In other words, a 10% larger disk will apply 10% more braking force, with the same size caliper and pad.

Bigger pistons = More force
Bigger pads = More friction = more force
Larger diameter disks = More force

But also, more force = More heat

But in most cases...Larger components, also results in better thermal management... Which is just as well

In this particular thread though, I think the general consensus is that if you overhaul a standard 944 S2 braking system, the amount of breaking force you will experience will be more than enough without an upgrade.

 

[Alexw]

I'll repeat what has been said, I refurbed the brakes on mine, removed platelift and had fresh fluid, discs and pads all round and removed a few corroded sections of steel pipe and replaced the flexi lines with stainless. The master cylinder is only a few years old, can't remember the slave but its in the receipt folder.
I did a good brake test a while after and it popped a contact lense out of my eye....

 

[simkin911]

ORIGINAL: Alexw

I did a good brake test a while after and it popped a contact lense out of my eye....

[]

 

[zcacogp]

Does everything think the erstwhile Joss Walker (the guy who originally asked the question) has got the message yet? []


Oli.

 

[Copperman05]

Possibly, perhaps he wants to talk about oil instead.[]

Edd

 

[zcacogp]

Oil or rust. Those are the usual ones.

Or perhaps how to activate the rear window wash/wipe ...


Oli.

 

[Indi9xx]

Awe.. but its not even turned into a heated debate yet..

 

[zcacogp]

Well I almost insulted ChrisG, but he was far too polite to respond in kind ... []

If Peanut would show up then I could call him a grumpy old fart again. And then he could call me a whippersnapper and we'd be away! Alternatively, if someone would like to put a hat on then I'll knock it off and ask them if they want a fight. That would probably do it. []

>LooksForHats<


Oli.