Mini Cooper S Brake Caliper Pistons
December 15, 2007 by donminimania
As far as cutting air slots in the caliper pistons, you don’t want to cut slots so deep that they could uncover the piston seal when the piston is pushed all the way in, that is the limit for the slot depth. The pistons in the picture above have four cuts, I would guess this gives about 25% reduction in surface area touching the pad. The slotting shown above looks shallow enough that those pistons could probably still be used with dust seals. This could be OK, but more slots will reduce the surface area further, and offer more paths for cooling air. I just mill flat-bottomed slots, my suggestion is 8 slots so you get around 50% reduction in area touching the pad. (From Mini Cooper Message Forum)
I took another look at Tarzwell’s Competition Mini book last night, he has more good ideas in his brakes chapter. Among other things, he suggests: air ducts
pack the piston with stove insulation, capped with a stainless lid
stainless sheet between piston and pad
reflective stainless heat shield between rotor and caliper
polish backing plate of brake pad
ceramic paint on caliper
machine grooves in caliper
open up caliper bridge to increase air flow to pads/pistons
