What Is the Difference Between Plug RCJ6Y & RCJ8Y?

by Cassandra Tribe
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Champion makes a wide range of spark plugs, including the RCJ6Y and the RCJ8Y types. Knowing which plug to use in a particular engine can be difficult, as the plugs are very similar. The only difference between plug RCJ6Y and RCJ8Y lies in their heat ranges. Understanding the similarities between them, however, can help determine if choosing the hotter or colder plug is necessary, as the two types are nearly interchangeable.


The first three letters of the plug code, "RCJ," indicate the type of resistor and shell design of the plugs. Both the RCJ6Y and the RCJ8Y use a standard resistor type and have a 14 mm thread, 3/8-inch reach and a hex nut that will either have a 3/4- or 13/16-inch size.

Firing End

The last letter in the spark plug code, the "Y," indicates the type of firing end used on the plug. The firing end is the end that the connected to the spark wire. Both of these plugs have a standard projected core nose.


Both plugs are meant for small engine applications. The standard firing end design of the plugs allow them to be used with many different types and models of small engines.

Heat range

The sole difference between the two plugs lies in their heat range capabilities, indicated by the numbers 6 and 8 in their code. Both the 6 and the 8 spark plugs are considered to be high-heat range plugs, with the 8 being the hotter plug. The heat range refers to the speed at which the plug can transfer heat or spark from the nose to the combustion chamber. The hotter plug will be better in an engine with a higher combustion rate temperature. The combustion temperature of the engine will be listed in the specifications of the engine or vehicle.

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