Howdy - I've got the P0303 code and I want to replace the plugs to start the trouble shooting. The last owner installed a 17% pulley kit from MiniMania, along with cooler plugs and new wires.

Here is the issue - every website that sells a plug kit says they come with "cooler" plugs, but nobody specifies what that means.

So, on my 03 R53 with a 17% pulley, what am I looking for?

 

Cooler plugs = JCW plugs....that is one step cooler than stock s plugs.

 

JCW spark plug is NGK part number BKR7EQUP.

The heat range of a spark plug is the range in which the plug works well thermally. The heat rating of NGK spark plugs is indicated by a number; lower numbers indicate a hotter type and higher numbers indicate a colder type (such as 7 for the JCW). A colder plug has a shorter insulator nose thus a shorter distance between the firing tip of the insulator, and the point where insulator meets the metal shell. Therefore, the path for the dissipation of heat from the insulator nose to the cylinder head is shorter and the firing end stays colder. The insulator nose of a colder spark plug also has less surface area that is exposed to more of the ignited gases and is harder to heat to higher temperatures.