Here is a detailed description of the exact caliper. The pictures that you see on the BMW and the 350Z both have a 6 piston on the front. The BMW has a 4 piston the rear. The 4piston rear caliper is exactly the same as the front 6 piston externally except internally it has smaller piston diameters to retain the all important balance we have been speaking of. Trust me BTW, it IS radial mounted
"This specially configured Superlite SL6R narrow body caliper features an increased bridge radius to allow proper pad alignment and bridge clearance for use with 13.00" to 14.00" diameter rotors. A special body design is used with 16 mm pads to provide the narrowest possible profile for tight clearance applications. Radial mounting simplifies adaptation and provides two planes of adjustment for accurate alignment over the disc. These calipers integrate "Big Brake" style with Wilwood's latest technology to generate big stopping power over a broad range of custom, high performance, and off road vehicle applications. The SL6R is well matched to the fluid output capabilities of many OE master cylinders and serves as the base caliper for Wilwood's 14.00" rotor front "Big Brake" conversion kits.
A key to the superior performance of the SL6R comes from the extremely durable and efficient body design. It is the product of computer generated solid modeling and FEA stress analysis technology. A reinforced radial transition from the piston bore housings to the closed end bridges has produced the strongest Superlite caliper bodies ever built. Additional strength and resistance to deflection comes from the four high-strength steel end bridge bolts. A fifth center bridge bolt provides even more overall strength and easy access to the pads without the need to remove the caliper from the mount.
SL6 calipers are assembled with one-piece stainless steel pistons and high temperature, square faced bore seals. Stainless pistons are used for their slow heat transfer properties and high resistance to corrosion. Slow heat transfer reduces the potential for heat related pedal fade and increases the service life of the fluid and seals. The high temperature square faced bore seals have the largest possible sealing area and provide controlled piston retraction on release. The differential bore six-piston configuration distributes the clamping load over the length of the pad to promote even wear in the highest temperature environments. This is especially beneficial to vehicles that often realize high temperatures during hard braking.
In addition, each SL6R is equipped with SRS bridge plates. SRS plates eliminiate all bridge wear caused by pad gauging and extend the service life of the caliper. The spring-loaded action of the SRS plates also eliminates pad rattle and dampens the harmonic vibrations that contribute to pad squeal. Two piece bleed screws and dampened fluid tubes are recess mounted to shield them from track debris and other potential damage sources. A full range of PolyMatrix pad compounds is available to match the brake response and heat range of any competition or sports driving application."
