Now this is where is gets interesting.... Mark has been schooling me on this subject and I have been doing a lot of reading. The maths gets a lot more difficult when you start changing part of the system but there are some simple rules:
To get a balance is the key factor, I'm no expert I have just been massing loads of data and so far I have found out:
- the larger the Master cylinder bore the lower the line pressure, but the more fluid you move.
- the lower smaller the cylinder on the caliper side the lower the pressure the revers is therefore also true.
This is why matching the systems, calipers, MC's are crucial, even more so when you don't have a split system as the rear also effects the front (Old single circuit), unless you use a valve to limit the rear pressure so your not locking the rears before the fronts.
Its also true that the larger the disc the further the caliper can be spaced which acts like a long bar when removing a nut so you get increase braking.
Overall there is a trend line that shows bigger is better as long as the MC is balanced with the setup. If the MC is too small you get a long pedal but you will eventually get the high pressure, too big and you get a short pedal but you will need to push very very hard to get the car to stop...
Then on top of this you get the effect of even pressure on the pads to ensure the best contact. If you look at the sq area of piston size of the 8.4" mini 2 pot setup against the minispares / metro 4 pot there is not a lot in it but the 4 pots produce a more even pressure across the pad and the pad area is larger.
Then enters heat ... as if you use a whacking great big pad with loads of pressure on a small disc the heat build up will reduce braking, hence why the 4 pots are alloy, why you can get vented discs... and new compound pads.
There is also brake feel which is driver preference, most road drivers prefer a short lighter pedal as is give confidence, buts its all down to choice.
A couple of useful links I have found along the way
http://www.calverst......they work.htm
http://www.calverst....siderations.htm
I have found this subject very interesting over the last couple of days. I have spoken to a few people including BG developments (01527 873716.) who have an interesting new pad compound from Germany called autobahn pads which they have said are good hot or cold.
KC is sending me the AP racing table which shows the data posted in the second link, which I have used to create a graph showing the trend line so that I could plot my Fiesta brake upgrade onto it, once I have the MC data is should help ID a good starting point for MC size... Talking to BG they were going with feel so pedal too long try a larger MC... AP step them up in small increments and they are available from a number of outlets.. expensive route at about £100 a MC....
Anyone else got any more data I can look at? The attached pic shows the Fiesta setup mapped on the trend line of the graph as I don't have all of the data, these figures are shown in RED. Once I have which MC was used to create the original AP deta from KC via AP it might make some more sense....
P.S I forgot to add weight of the car and wheel size also effects performance of your stoppers. e.g small wheel large disc better than large wheel small disc... Plus loose some weight in fact I will go for a run tomorrow 
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Hi Gr4h4m,
That is interesting, I just sent you a PM.
It is true that you get more feeling with the brake pedal when a smaller MC is used. Most Zcars builders are using a split brake system so the rear brake pressure can be adjusted with an inline Wilwood brakepressure adjuster or the KAD adjustable brake bias box with 2 separated MCs.
For what I have calculated with a very simple MS Excel sheet, is that a 3/4" MC give very little brakepedal movement and a quick brake response so there is little space for errors and less brake control because the brake will lock up quickly. The 5/8" MC would be a good choice for brakepedal movement and brake control. The 1/2" MC should give lots of pedalmovement and control, but you must 'put the pedal to the metal (or floor)' for a lot of pressure. I do not think that this is good, because you would never reach maximum brake pressure.
I think that all our thoughts about braking will help lots of other Mini (re)builders, especially the (re)builders who wish to have a massive brake system for their fast Minis.
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