- The piston is 87mm, that's 1mm larger sized compared to typical 86mm, and the fabric is light-weight and robust A4032 cast aluminum alloy. The desired clearance of 0.Still, the two are really comparable, as well as RB25 is de facto no slouch. You could think of the RB25 vs the RB26 as similar to the 1JZ vs 2JZ discussion. The RB25/1JZ are a littl