I'm using xp8 on the fronts in Jcw calipers (4-pot) mostly road use but occasionally track as well (30/30)
not as dusty or as noisy as some would have you believe
but perhaps I have lower standards

It is interesting the different experiences that people have with the same brake pads. My experience with the 1521’s was that they had very little bite and it took a lot of force to get any stopping power out of them. As a result I never got them into an agressive braking situation. I wonder if Carbotech changed them since I last used them....

That said, overall my opinion of Carbotech pads is otherwise very positive. The Carbotech pads are reasonably street friendly and their dust is less agressive than other high temperature pads. I have driven the XP10s on the street. They perform very well, even cold and my only negative observation is that they are a bit noisy (as in “squeals”). I have run the XP8s in the rear for multiple summers (I leave them in during track season and only change the fronts) and they made a great street pad. A bit dusty, though, but not as bad as the stock MINI pads. The Carbotech pads are also not as agressive on rotor wear as some other pads (Hawk, for one). I would suggest running the Carbotech XP8 all the way around. I know that the conventional wisdom is that the rears don’t do any braking, but, really they do and a good pad in the rear will take some of the load off the fronts (that is, the fronts won’t heat up as much). Glock pads are very similar and their equivalent would probably do just as well.

It will be interesting as to what you come up with... although right now, over heated pads shouldn’t be an issue with the sub-zero temps coming up...

What is your though as to what the GP2 master cylinder will do for you? I know it is different from the one use on the S and JCW, but not familiar with how it is different.

When I first got into taking my MINI to the track, my friends who had a lot of track experience at that time pushed on me to get the Carbotech XP10s (glad they did as the Hawk HPS pads I tried only lasted 2 sessions). They were also familiar with the 1521s and, according to what they had read/heard, Carbotech had been getting complaints about the bite with those pads. “Unofficial” they suggested to people to use the AX-6 (the autocross pad) for the street. I used the 1521s as Carbotech is adamant about not mixing their pad materials with other brands of brake pad materials.

Noise will always be an issue with higher temperature capable pads. The higher the temperature capability, the more likely a pad is to squeal when it is cold. This is the main reason that all of the race pads say “not for the street”. The HP+ is a boarderline capable race pad and it will squeal. Some pad are worse than others. The 1521 is a less capable pad than the HP+. I would recommend the XP8 if you are going to try the Carbotechs.

let us know how you make out...

Thanks for the info about the GP master cylinder.

With the piston in the master cylinder being larger, it will move more fluid from the master cylinder to the caliper for the same amount of pedal travel, which will cause the reaction at the caliper to be more immediate, as you said. The Wilwood setup does the this same thing but by putting smaller pistons in the calipers. I find that modulation is still very good, and it makes heal and toe a bit easier to perform as there is less brake pedal movement to deal with. What I don’t remember is how much of change there was when I changed to the Wilwoods. I also don’t recall it being a real radical change either. I can say I am pleased with it. If the GP master cylinder makes a similar change to the “feel”, then I would think it would be a good move to put it in.

Xp8 are streetable, but they are hard on discs, so worth a measure now and at 10k for your "review"

Carbotech XP10s.

The Carbotech brake pads are very rotor friendly, for a race brake pad. My experience with the XP10s on the street is that they work well, a bit noisy and dusty. In general, people match those with XP8s on the rears.