Call me what you will, but I only fully turn ESC off for autocross. I leave it on dynamic on track. I'm not trying to wreck a new car to shave half a second of time at a HPDE.
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7
Consolidated Macan Brembo upgrade thread (READ FIRST POST)
- Thread starter GTIfan99
- Start date
Call me what you will, but I only fully turn ESC off for autocross. I leave it on dynamic on track. I'm not trying to wreck a new car to shave half a second of time at a HPDE.
Will_
Autocross Champion
- Location
- SF Bay Area
- Car(s)
- 2017 GTI S DSG
Yea, I don’t mind leaving it on, just noting where it kicked it. I felt it two other times today, both times when I came in a little too hot to a banked corner, let off and then slid a little and had to correct. I could feel the brakes apply but it did a good job, kept it very stable and easy to catch.
scrapin240
Drag Racing Champion
- Location
- IzzaGolf
- Car(s)
- Golf
On my R it needs to be turned off...about 4 second difference in lap times.
Girodisc Titanium shims came in
Girodisc Titanium shims came in
Attachments
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Will_
Autocross Champion
- Location
- SF Bay Area
- Car(s)
- 2017 GTI S DSG
Wow that’s a huge difference. Could just be me not pushing hard enough, I’m definitely not fast yet.
scrapin240
Drag Racing Champion
- Location
- IzzaGolf
- Car(s)
- Golf
Also brake wear is much less.
emichel6888
Go Kart Champion
- Location
- TX
Replaced the boots and seals. The boots were in rough shape, with only one kinda being held together still, most were just the part that seats on the caliper and the part that hooks onto the piston, nothing in between
Stock seals still looked pretty good.
On a side note. Looks like my powdercoater made an error when putting the calipers back together. They just put all the silver pistons into one caliper, and all the black ones into one. The two silver pistons on the inner side seemed to have suffered a lot of heat and there's a bit of weird pitting almost on the back of them. Seems like the black ones are meant to withstand more heat?
@pseudorealityx did you feel like the pistons slid in a lot easier with the RB seals? My friend said it felt super "loose" compared to the stock seals.
What ever happened with your low brake pedal? Did this help? Are the inner seals stock or high temp silicon as well?
Haven't had time to bleed properly yet. We wrapped up pretty late and wasn't going to perfectly bleed brakes in the dark. Also don't have plans to go back to the track anytime soon, so I wouldn't be able to fully tell till I go back
They looked like the stock ones, but not sure how I'd be able to tell what material Racing Brake made them out of.
scrapin240
Drag Racing Champion
- Location
- IzzaGolf
- Car(s)
- Golf
From everything I've researched the factory seals don't really fail, it's the dust boots that usually fail. The factory seals still usually hold up to the heat even when the dust boots are destroyed.
The RB seals didn't seem like they were anything special vs the high temp dust boots that they make.
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emichel6888, I've added a link to your valve project in the first post. Thank you for all your work on that project. I'm looking forward to trying it.
emichel6888
Go Kart Champion
- Location
- TX
Hey on another subject regarding these calipers, I have never really looked this closely at brake technology before, I am learning a lot here.
I noticed the pistons are offset in the calipers, the reason for this is; as the leading end clamps the rotor it starts creating a lot of heat, as the rotor moves towards the trailing edge it just keeps getting hotter and hotter until it passes the pad area and starts to cool again. As the rotor heats up more pressure is required to create the same amount of friction/wear. This is why many multi piston calipers use smaller pistons on the leading edge, to give more even friction/wear across the pad area.
This caliper does not use offset piston sizes, but they did offset the pistons so they are positioned more towards the trailing edge of the pad area. Unfortunately because these calipers are designed for the rear position and we are using them on the front, we essentially have them backwards putting more clamping force on the leading edge rather than the trailing edge, which is the exact opposite of what you want for optimum even pad friction/wear. I recently checked my pads and I am definitely seeing more wear on the leading end of the pad, it is not horrific, perhaps 10% but still...
So why are we running these calipers backwards? Well because the cross over tube only fits on one end and you want the bleeders on top of course. The bleeder fittings and the cross over fittings are the same size (I checked), the problem is that the fitting positions are different from each end of the caliper so you can't just swap the bleeders and crossover tube. But you know what? That cross over tube is just a piece of tubing with a couple of 10M x 1.0 flare fittings, it would not be difficult at all to make a custom cross over tube that would allow us to swap ends and use these calipers in the way they were intended. This would improve performance and give more even pad wear.
I have time off next week so I think I am going to do this and swap them over. I will of course take pictures and let you know how it goes.
I noticed the pistons are offset in the calipers, the reason for this is; as the leading end clamps the rotor it starts creating a lot of heat, as the rotor moves towards the trailing edge it just keeps getting hotter and hotter until it passes the pad area and starts to cool again. As the rotor heats up more pressure is required to create the same amount of friction/wear. This is why many multi piston calipers use smaller pistons on the leading edge, to give more even friction/wear across the pad area.
This caliper does not use offset piston sizes, but they did offset the pistons so they are positioned more towards the trailing edge of the pad area. Unfortunately because these calipers are designed for the rear position and we are using them on the front, we essentially have them backwards putting more clamping force on the leading edge rather than the trailing edge, which is the exact opposite of what you want for optimum even pad friction/wear. I recently checked my pads and I am definitely seeing more wear on the leading end of the pad, it is not horrific, perhaps 10% but still...
So why are we running these calipers backwards? Well because the cross over tube only fits on one end and you want the bleeders on top of course. The bleeder fittings and the cross over fittings are the same size (I checked), the problem is that the fitting positions are different from each end of the caliper so you can't just swap the bleeders and crossover tube. But you know what? That cross over tube is just a piece of tubing with a couple of 10M x 1.0 flare fittings, it would not be difficult at all to make a custom cross over tube that would allow us to swap ends and use these calipers in the way they were intended. This would improve performance and give more even pad wear.
I have time off next week so I think I am going to do this and swap them over. I will of course take pictures and let you know how it goes.
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The calipers aren't set up with one of each piston on each side (to support your theory that the coated on is to take the extra heat of the leading/trailing edge). The coated (black ones) are both on the inner side of the calipers, while both of the non-coated ones are on the outer side.
emichel6888
Go Kart Champion
- Location
- TX
Oh well, then what is the theory on why they are different? Is it just possible they were just installed wrong from the factory? It is not like things like that don't happen on occasion right? I work for a high end medical imaging supplier (which is heavily regulated) and you would be surprised how often mistakes like this happen, unless there is some other explanation?
Regardless, the offset pistons is definitely an issue that can be easily corrected with a custom cross over tube, so I am going to do it regardless.
My buddy has opened 3 sets of these calipers already. Unless it was oktoberfest over at the factory when all 3 sets were made, I doubt it's an error.
The inner part of the caliper definitely sees more heat than the outer. On the caliper that my powdercoater messed up putting back together. 2 of the 4 non-coated ones were damaged from seeing more heat, and they were installed on the inner side.
emichel6888
Go Kart Champion
- Location
- TX
Well, I certainly could be wrong about the different piston coatings, but correcting the offset alone might be worth doing. I have already decided I am going to do it, it may not be a huge difference but...
As for the pistons, I am not sure what to make of that, perhaps it is for temperature differences, or maybe something else entirely. I have not seen or been able to find any information about why a manufacturer would use different piston coatings on the same caliper. Most seem to use just one type of coating. I noticed a lot of OEM pistons seem to have a similar dark coating for all the pistons, while most of the aftermarket performance calipers are generally much lighter.
Recently as I was playing around with these RPV's I measured that the piston retraction on the inside pistons was considerably less than the outer pistons. Which if that darker coating causes more seal slip that would make sense. I assumed the piston retraction was more or less the same inner and outer, it is not, and the different pistons seems to be the reason why. Is this just Porsche's way of tuning piston retraction/brake pedal response? Or is it a temperature issue?
You would think if was a temperature issue between inner and outer caliper pistons we would see something like this on other calipers. However from what I can tell it is not a very common practice.
In trying to research this issue I did find this post from some guy Chris in the UK, he seems to know an awful lot about brake calipers and piston materials/coatings. If this sort of thing interests you:
http://forums.pelicanparts.com/pors...m/914609-why-stainless-caliper-pistons-2.html
I have been interested in caliper pistons for some time now and have been looking at the parts available in the market and tried to reach some conclusions about the 'best' materials.
To start with I think it is important to review the objectives we have with regard to the duty of the brakes and what is required from the pistons.
There is a view that the 'job' of a caliper seal is not only to prevent fluid leakage but to retract the piston when pressure is released as this stops the pad from rubbing on the disc and is good for economy.
I have to say that I don't agree with this analysis and that pad retraction is generally a bad thing and that the effect of this action is similar to 'pad knock off' and increases pedal travel.
It is common to fit race calipers with either residual springs behind the pistons or with low pressure check valves to eliminate this problem.
The seal is always responsible for a small amount of piston retraction and this will vary depending on the surface finish of the piston, the stored energy in the seal due to radial compression and even the fluid used to lubricate the piston during initial assembly.
Using brake fluid, for example, increases seal friction compared to the correct assembly grease and this influence will last for many thousands of miles.
I believe that good quality pistons should have a high level of surface finish, relatively low thermal coefficient of expansion(TCE), Have relatively low Heat Transfer Coefficient (HTC),be relatively corrosion resistant and have good wear resistance.
If we review the materials that have been discussed then the basic properties are easy to find but there are influences that also need to be considered .
1. Conventional Steel
Typically chrome plated, modest expansion, modest heat transfer, huge amounts of comparative test data available and in every sense have stood the test if time.
A conventional medium carbon steel in an 'as rolled' condition is unlikely to have adequate wear resistance.
The quality in terms of dimensional control and surface finish of some aftermarket parts is questionable but Porsche Caliper Pistons supplied by BudWeg seem to be reasonable and do a good job.
2. Aluminium
As discussed many modern caliper use Aluminium Alloy pistons.
They are easy to manufacture, relatively light and hence quite low cost.
The down side is that they expand more than a conventional steel piston TCE is around twice that of conventional steel , they transfer heat easily into the brake fluid HTC is 5 times greater than conventional steel.
They also don't wear very well unless they are hard anodised. This means that they will need to be centreless ground after anodising as the increase in surface roughness caused by this process will make the piston grab the seal and significantly increase piston retraction.
Modern multi-piston calipers with substantially thick pads clearly cope with pistons of this type but old-fashioned designs which have higher caliper piston temperatures may not do quite so well.
My concern with Aluminium pistons and old fashioned calipers concerns the clearance change when the piston expands.
If the piston has an identical size to the steel piston it replaces then as it heats it will increase the radial compression. This will increase pad retraction and in the limit the piston could stick if temperatures became very high.
If cold clearance is increased to eliminate this issue then seals may wear quite quickly if the car is driven gently and the brakes not heated to provide the optimum value.
This is possibly only an issue for race or trackday cars that are hard driven.
I would admit to never have used any aluminium pistons in early 911 calipers.
3. Stainless Steel
This type of piston is typically manufactured from EN303 which is a free-machining Austenitic Stainless Steel and will provide a high standard of surface finish without centreless grinding and good corrosion resistance.
Its HTC is about one third that of conventional steel so the rate at which the brake fluid heats will be slower and this could be a benefit on a race car.
The problem with Austenitic Stainless Steel is that its TCE is similar to Aluminium so it expands by around 70% more than conventional steel and the same seal issues that concern me for Aluminium will not differ greatly for EN303.
There are Martensitic Stainless Steels available but these don't machine as well and would need grinding. The TCE would, however, be the same as conventional steel.
We did buy a batch of Stainless Steel Pistons from a supplier in the USA and had very mixed results. (20 Caliper sets)
Many or them worked well in normal road cars but about 50% of the ones fitted to Race cars stuck during high speed practice and did cause us some difficulty.
This problem is what caused us to look more closely at these issues.
4. Titanium
There are several grades of Titanium available in the market place and the traditional 6AL4V Grade 5 material is the optimum choice.
This alloy has excellent strength, it has a very low HTC - 50% lower than Austenitic Stainless Steel so about 6 times lower than Conventional Steel and 30 times lower than aluminium.
Its TCE is about the same as conventional steel (within 5%) so all seal behaviour should be identical to the original part.
Apart form cost it looks like a good material but it is prone to wear in rubbing seal applications.
The fix for this is to coat the piston and the typical finish is to use a Titanium Carbide applied in a PVD chamber.
This finish is as hard as DLC and provides an extremely smooth surface.
5. Phenolic Resin
This material can be quite hard and have virtually zero HTC but depending on the filler does expand about 4 time more than even aluminium.
It will absorb water and loose strength so the part of the piston outside the dust bot could deteriorate.
I am sure that some materials such as Torlon may work but for small aftermarket quantities the testing needed to be 100% confident would be huge and difficult to justify.
5. Silicon Nitride
It is possible to place silicon Nitride plugs into the cavity in the piston and these will insulate but I have never tired this idea and I am not sure about how 'square' this arrangement would be in practice.
We eventually decided to make our own 6AL4V Titanium Pistons.
they are manufactured on our behalf by a sub-contractor who manufactures pistons for AP Racing.
They are centreless ground polished and Titanium carbide coated and seem to work well.
Sorry to bang on but I hope some detail was worthwhile.
emichel6888
Go Kart Champion
- Location
- TX
In fact if it is more about tuning the piston retraction, one could try to get four more of those darker slicker coated pistons and swap out the lighter outer pistons. That combined with the RPV's would help even more with brake pedal response! Or as he mentioned you could possibly use some sort of lube on the inner seals to reduce piston retraction, but I am not sure how consistent that would be.
Anyone know where I could buy a set of these pistons?
Anyone know where I could buy a set of these pistons?
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