2020 Rule Changes SECTION 1A:STOCK, ENGINE:1,PISTONS (Page 5) (12/4/2019)OEM or NHRA-accepted aftermarket replacements permitted provided such items comply with all requirements set forth in this section. Aftermarket pistons permitted, may be forged, billet or cast and must retain the OEM as-cast or as-forged head configuration. The manufacturer or ID number must remain unaltered and fully visible to determine the correct application. Intake side of head may be +/-2 degrees fromRead More