Mahle Motorsport Piston Set for BMW S54 engine. 87.50mm Bore, 91mm Stroke, 139mm Rod, 21mm Pin. Choose 12.5:1 or 9:1 CR for N/A or Forced induction applications. CR calculated at 0.25mm below deck and 0.69mm head gasket thickness. PowerPak Plus 2618 Alloy & Hard Anodized Top Ring Groove For Extreme Duty Applications.