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NISFAN said:
Chris,

Thanks, quick question, on a 1200Kg GTS, 4 pot or 6 up front?
I used 4 pots as I had some big Brembo Group C Porsche ones, new, knocking about. Whatever you can get cheap, that have sensible piston sizes and offset, basically. Avoid anything other than Brambo, AP or Alcon. You will find the others either flex, have very limited pad choice, weigh a ton, or are otherwise inferior.
 

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You need to match the front and rear balance correctly, so piston size depends on what calipers and discs are on the back, what diamater discs are on the front, if you are keeping a single master cylinder, or converting to dual cylinders and a bias bar, whether you are keeping the servo, to a lesser extent what pad compound you intend to run, blah blah.. Very complex, to make a worthwhile reply I would need a LOT more info. If in doubt buy something like the AP six pot kit, and save a lot of headaches and experimenting. To be frank though, the AP six pot kit, on a full weight GTR, on stock rear brakes, is not big enough, I used to get through a set of those front discs nearly EVERY track day, through heat crazing, especially in the wet, when they would ALWAYS be dead in a day. Getting cold air to the front brakes on a GTR, with driveshafts in the way, is virtually impossible, as done correctly you need to DUCT into the eye of the discs, where the outer CV joints and hub shafts are. I have pics somewhere of a one day old AP disc, after a wet Oulton day. The thermal shock kills them, from water splash. See:

ftp://ftp.chriswilson.tv/cracked

As I said, expensive hobby, running overweight, under braked, powerful road cars on track days :)
 

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Discussion Starter #10
Chris, I already got a set of 4 pot AP's for the rear, but with the small 1" pistons, together with (IIRC) 330mmx32mm discs.

For the moment I'll be using the stock master cylinder/booster, but eventually will fit a new pedal box with twins and balance bar. (No servo???)

I will be running a low/stiff suspension set up, so hopefully won't get as much weight transfer = high % of rear brake effectiveness. (295 rear tyres)

I was thinking of using the 330mm (13") discs and the bigger pistoned 4 pots up front, for cost reasons, and don't think I need 6 pots on a 1200kg car. (Unless I run slicks)

Car use is track days (5-6 laps maximum at a time), time attack single laps, and sprints.
I guess the 5-6 laps is the biggest challenge due to heat buildup.

I also want maximum brake feel, as no ABS on mine. I'm not sure whether 6 pots will be more or less snatchy?

Any thoughts?
 

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You can get nicely ducted air directly to the eye of the disk. I`ve used a 3inch ally pipe, cut to fit the profile of the bottom balljoint and rear of the bell, bolted to the inside face of the AP caliper. 3inch pipe from brake ducts in bumper.

Definatly works. Disks now last 4-5track days (with an appropriate pad) with minimal heat crazing and no warping...

I`ll post a pic when I can......
 

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NISFAN said:
Chris, I already got a set of 4 pot AP's for the rear, but with the small 1" pistons, together with (IIRC) 330mmx32mm discs.

For the moment I'll be using the stock master cylinder/booster, but eventually will fit a new pedal box with twins and balance bar. (No servo???)

I will be running a low/stiff suspension set up, so hopefully won't get as much weight transfer = high % of rear brake effectiveness. (295 rear tyres)

I was thinking of using the 330mm (13") discs and the bigger pistoned 4 pots up front, for cost reasons, and don't think I need 6 pots on a 1200kg car. (Unless I run slicks)

Car use is track days (5-6 laps maximum at a time), time attack single laps, and sprints.
I guess the 5-6 laps is the biggest challenge due to heat buildup.

I also want maximum brake feel, as no ABS on mine. I'm not sure whether 6 pots will be more or less snatchy?

Any thoughts?

4 or 6 pot will be fine, probably something like 355 mm didc would be better on the front, the rear discs are a big diameter, you could end up with too much rear bias. I have some AP and Willwood propertioning valves doing nothing if you need to take bias off the back. Spring rate will make NO difference to weight transfer. 5 or 6 laps is nothing, so you don't need to go too wild, i expect my brakes to do 20 full speed laps with zero fade. The bigger pad area that a 6 pot caliper usually gives is probably not needed on a sprint car, so if you find 4 pots at the right price, buy `em.

My next step is to make a bias bar set up, remove the servo, and have proper bias adjustment. The bar assembly is nearly done, need to make a plate to replace the servo back face, and decide on cylinder sizing as a starting point.

I run 225 fronts and 255 rears, on 8 and 9 inch rims.
 

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Discussion Starter #13
Cheers,
I will be fitting a set of tilton pedals at some point with all the cylinders and bias bar (kit). I believe you can fit a servo onto this set up too, if you have room. Floor mount kit?

Do 6 pots generally give more feel and progression, or less? I've heard conflicting comments.

I do plan to use a rear bias valve, I have a tilton one available already, thanks.

20 hard laps!!!! no wonder you have a miniture replica of the grand canyon in your discs. Are you entering some sort of race series?

How come racing GT cars seem to have pathetically small discs that are thin with no cooling channels, and last a long time? I'm sure they look like steel discs, so not carbon or ceramic before anyone says.
 

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Discussion Starter #14
Chris Wilson said:
.......if you find 4 pots at the right price, buy `em
End of Nextel cup series season, loads of calipers for sale. Brand new change of sponsor type deals going on. lol.
Also 6 pots, but big hike in price due to supply and demand.
 
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