The heat range of a Champion spark plug is indicated within the individual part number. The number in the middle of the letters used to designate the specific spark plug gives the heat range. For instance, if a Champion spark plug's number is RCJ6Y, the heat range is 6.
With Champion spark plugs, a higher number in the middle of the part designation designates a hotter spark plug. Most spark plug manufacturers indicate a spark plug's heat range within the part number; Bosch, Denso and NGK also place the heat range designation within the middle of the part number. Other spark plug manufacturers place the heat range at the end of the part number.