- The piston is 87mm, that's 1mm larger sized in comparison to the standard 86mm, and the fabric is light-weight and robust A4032 solid aluminum alloy. The specified clearance of 0.It’s not unheard of for GT-R fanatics to sidetrack and discuss Z-tunes and 400Rs. Lovers on the brand are thoroughly knowledgeable of those constrained-operate GT-Rs a