RRD M50/S50/M52/S52 Forged Racing Pistons, 138mm Honda RodM5X lightweight NA pistons utilizing the Honda B18C connecting rod! The Honda B18c rod has the exact same big end diameter and width as an S52, but are 138mm long and use a 21mm wrist pin like a euro S50 or s54. By utilizing the 21mm pin and longer rod, we can reduce the reciprocating mass of the piston pin by reducing the mass of the pin and lowering the compression height. This reduces inertial load. By using the Honda rods we get a much wider