GT4 or modded Cayman R

[fioran0]

Have you got the GT3 master cylinder fitted yet?
This would be the first port of call on the cayman if it were me. The larger MC will reduce pedal travel and require more effort which is definitely a good thing in its case.

[J-P]

fioran0 said:

Have you got the GT3 master cylinder fitted yet?
This would be the first port of call on the cayman if it were me. The larger MC will reduce pedal travel and require more effort which is definitely a good thing in its case.

No I've got, better pads, brake fluid, GT3 brake ducts, as well as braided hose. GT3 MC is definitely the next thing on the list from braking perspective, I'll prioritise it if it's going to improve brake pedal feel (which to be honest is one of the few things about the car that I really don't like).

[bcr5784]

J-P said:

Thanks for the above, Neil. All very interesting and leads me to the conclusion that I definitely need expert help in this area.

On a separate note SVP is thinking about being able to have a brake bias box.

What is brake bias? I won't be racing the car but wondered whether or not it would add to the experience? Does it mean changing the braking force applied to each axle? If so, does that mean you need to amend for every corner?

Thanks

Like others have said, it's about changing distribution of braking between the front and rear. It's extremely desirable when racing - you need to bias braking to the rear in the wet and the front in the dry. BUT with ABS this is not needed, and so its value is much reduced. It is probably a waste of time (with ABS) UNLESS you need to use trail braking to get turn in AND you can't get the degree of turn in you are trying to get. I think it almost certain that you won't need it since you are asking the question - and if you do you won't be asking the question!

Edited by bcr5784 on Tuesday 6th January 19:34

Edited by bcr5784 on Tuesday 6th January 19:39

[J-P]

bcr5784 said:

J-P said:

Thanks for the above, Neil. All very interesting and leads me to the conclusion that I definitely need expert help in this area.

On a separate note SVP is thinking about being able to have a brake bias box.

What is brake bias? I won't be racing the car but wondered whether or not it would add to the experience? Does it mean changing the braking force applied to each axle? If so, does that mean you need to amend for every corner?

Thanks

Like others have said, it's about changing distribution of braking between the front and rear. It's extremely desirable when racing - you need to bias braking to the rear in the wet and the front in the dry. BUT with ABS this is not needed, and so its value is much reduced. It is probably a waste of time (with ABS) UNLESS you need to use trail braking to get turn in AND you can't get the degree of turn in you are trying to get. I think it almost certain that you won't need it since you are asking the question - and if you do you won't be asking the question!

Edited by bcr5784 on Tuesday 6th January 19:34

Edited by bcr5784 on Tuesday 6th January 19:39

That's interesting. At Snetterton a couple of years ago, the CR was great apart from the hairpin, where I did need to trail brake and the car still under steered. It really annoyed me actually, is this something that brake bias could have helped with?

[bcr5784]

J-P said:

That's interesting. At Snetterton a couple of years ago, the CR was great apart from the hairpin, where I did need to trail brake and the car still under steered. It really annoyed me actually, is this something that brake bias could have helped with?

In theory, possibly - but there may be other factors at work.

[J-P]

bcr5784 said:

J-P said:

That's interesting. At Snetterton a couple of years ago, the CR was great apart from the hairpin, where I did need to trail brake and the car still under steered. It really annoyed me actually, is this something that brake bias could have helped with?

In theory, possibly - but there may be other factors at work.

Might need to try a car with it and see if it makes any difference. Cheers

[fioran0]

J-P
If you have done all that work you need to get the GT3 mc on there. It's almost criminal you haven't.
It will give you a proper brake pedal once you get it on. The one in there presently is long!

Cmoose
I've no idea on price, £300 or so most likely. TRW make the part however. I'm sure with an afternoons effort one could source it via an alternative channel for half the price.
Its a fairly easy swap if you are handy, though I would probably pay someone as bleeding brakes is possibly the dullest car work around.

[J-P]

fioran0 said:

J-P
If you have done all that work you need to get the GT3 mc on there. It's almost criminal you haven't.
It will give you a proper brake pedal once you get it on. The one in there presently is long!

Cmoose
I've no idea on price, £300 or so most likely. TRW make the part however. I'm sure with an afternoons effort one could source it via an alternative channel for half the price.
Its a fairly easy swap if you are handy, though I would probably pay someone as bleeding brakes is possibly the dullest car work around.

I'll get it done - sounds like a no-brainer and not too expensive either.

[ajondyh]

anonymous said:

[redacted]

When I had mine done in October 2013 it was £302.31 + VAT for the MC part number 997.355.910.30. It does make an incredible difference to the pedal feel. I also fitted GT2 brake ducts and titanium heat shields and used Mintex M1166 pads with Castrol SRF fluid. Brakes have never been a problem since

To fit the GT2 ducts you need to cut a slot as shown in the picture

[n5tew]

http://sharkwerks.com/porsche/987-cayman-and-boxst...

[J-P]

Interesting - like the look of that Tubi exhaust. I'm looking forward to trying the SVP car in a couple of weeks.

[fioran0]

FWIW, the 997 GT3 MC is the same on both the 997.1 GT3 and the 997.2 GT3. Its also the MC used on the 997 Turbo/GT2.
Its not particularly relevant if you are going to get from an OPC, but it may prove useful if you are going to source elsewhere.

[fioran0]

J-P said:

Thanks for the above, Neil. All very interesting and leads me to the conclusion that I definitely need expert help in this area.

On a separate note SVP is thinking about being able to have a brake bias box.

What is brake bias? I won't be racing the car but wondered whether or not it would add to the experience? Does it mean changing the braking force applied to each axle? If so, does that mean you need to amend for every corner?

Thanks

No problem. At least you can refer to it if you need help sleeping.

As already mentioned by others, brake bias is the front/rear distribution of braking effort. I'm not following the brake bias box bit though. Do they mean they will give you adjustable bias control or just make a bias change to the car?

With an adjustable bias control you can change how much braking effort is sent to the front and to the rear. Usually the control is in the cabin and you can do it on the fly.
You could adjust it for each corner, like an F1 driver, or you could set it up for different conditions. In practice its as likely to see you heading down the road backwards as it is to give you an involved drive . If you tweak it and end up with the rear locking before the fronts its definitely "code brown".
A single hit bias change would simply involve adjusting the system (usually by fitting some sort of proportioning valve) so that the current brake force split becomes something else.

Its an interesting suggestion. The bias on your car, as with all the modern Porsches since 2005, uses an electronic bias adjustment as part of ABS. Its actually highly active and very proactive (as is ABS as well). While the driver doesn't feel anything at the pedal, under hard braking the electronic bias actually pretty rapidly reduces rear system pressure sending everything to the front after the initial pedal pressure is input. You can see it pretty clearly if you run data logging on the brake lines.

As such, any physical adjustment to bias (either allowing adjustable bias or a one time bias change) would usually be overruled by the electronic bias control unless the ABS was removed completely or somehow reprogrammed.

[ajondyh]

fioran0 said:

FWIW, the 997 GT3 MC is the same on both the 997.1 GT3 and the 997.2 GT3. Its also the MC used on the 997 Turbo/GT2.
Its not particularly relevant if you are going to get from an OPC, but it may prove useful if you are going to source elsewhere.

It's available as a std TRW part but I don't have the part number to hand, however I went for the Porsche part and was fitted by OPC to avoid any warranty issues

[ajondyh]

anonymous said:

[redacted]

Not sure which part you want me to comment on. All I can tell you is my brakes are perfect now. Take advice from others if need be but it wont affect the way my cars feels for me thanks

[ajondyh]

anonymous said:

[redacted]

It's not 'rock hard'.... you're reading "Americanisms" It's a lot firmer than before and doesn't travel so much when used hard for long sessions. Basically, you have a "Good" pedal

I stopped reading the USA forums a while ago as they have very different/Strange ideas compared to us here in Europe. (They probably think the same about us)

[fioran0]

cmoose,

Force applied by your foot on the brake pedal creates a pressure in the master cylinder. For any given brake pedal force a larger master cylinder will create less pressure than a smaller master cylinder.
Pressure = Force / Area so increasing area reduces pressure if force is fixed.

Pressure created by the master cylinder then acts upon the brake pistons which (pressure acting on an area) apply force to the brakes. This force is directly related to pressure since piston area is fixed. Applying X pressure will generate Y Force.
Since a larger master cylinder generates less pressure for a given pedal force, in order to generate Y force using X pressure, greater force must be applied at the pedal.

In addition to generating pressure, the master cylinder must also move a volume of fluid. Volume = area x length. To achieve a given volume, a master cylinder with a larger area requires less length of travel than a smaller master cylinder.

As a result, a larger master cylinder requires greater pedal pressure and less travel to achieve a required brake force in comparison with a smaller master cylinder.

Edited by fioran0 on Wednesday 7th January 01:45

[PR36]

I have a ton of mods on my 987 CS inc the gt3 mc and steel lines. The spongy pedal feel is reduced and it's a good improvement. It also helps the feel if you change the stock pedal covers, I am using rennline pedals. My only brake mod left is to fit pagid rs yellows and I'm more than happy with this for the road.

[UH-Matt]

While modding the R will be fun, and you could potentially end up with something better, it's a lot of dosh to lose.

I've modded plenty of cars including Lambo's and you can kiss goodbye to most of the money you put into mods when it comes to selling on, it can also limit the market of people who are even interested in the car.

If you can get a build slot on the GT4 I would definitely go that route, as you will end up with one hell of a car, and it might just appreciate over time rather than be throwing money in a drain.

[fioran0]

cmoose,

I ran quick calculations on the MC change out to give you an actual number on the change in pedal force. It may prove useful given your questions (and for others too of course).
For a Cayman with steel brakes, changing the MC to a GT3 version will see you need to increase pedal force by 27.5% to achieve an equivalent pressure using the stock MC.
For a Cayman with PCCB, changing the MC to a GT3 version will see you need to increase pedal force by 12.1% to achieve an equivalent pressure using the stock MC.

For 40 bar pressure, a steel cayman needs 20 lbs force and a PCCB cayman needs 25.28 lbs force. After GT3 MC change out the required forces are 25.52 lbs and 28.35 lbs respectively. The difference is down the different booster assists between the PCCB and steel cars.

As a side note. I was surprised at the amount of assist from the brake boosters on these cars. The steel cayman has an assist of 5, the PCCB cayman has an assist of 4.5.
Thats much more than I was expecting to see. For reference, the 986/996 used 3.85 and the 996 GT3 used 3.15. A 986/996 would need 26 lbs force to achieve 40 bar pressure while the 996 GT3 would need 36 lbs force.
Changing the booster at the same time would also be of benefit if one wanted to firm up the pedal further and could find one with less assist to physically fit in. For the steel cars, even using the PCCB booster (while still not great) assuming its probably an option would yield an improvement. Pedal force would increase to the same 28.35 lbs as the PCCB car post mod. Thats an increase of 41.5% pedal force over the original steel pedal/booster combo.