Spark Plug Heat Range

I recently posted a question to the Triumph Mail List about the various heat ranges for spark plugs. Within an hour I had my answer from a number of folks that I'd like to share with everyone. I also found this cool site http://www.4secondsflat.com/Spark_plug_reading.html  that helps you to read plugs. I didn't know that there are marks left on your plugs to indicate the correctness of your timing.

From Andy Mace:

RN7YC; now Champion 332
RN9YC; now 415
RN11YC4; now 322 (also given for N10Y)
RN12YC; now 404
RN14YC; now 405

Andy referenced www.sparkplugs.com where I pulled the table below showing the Champion naming convention for their plugs. The higher the number, the hotter the plug.
The table can be found at (http://www.championsparkplugs.com/images/champion.jpg)

Jay Welch explained that NGK plugs go like this:

NGK BPR5ES = hot
NGK BPR6ES = stock
NGK BPR7ES = cool
NGK platinum plug = BPR6EVX

He also added that the Triumph 6 cylinder engine uses a 14mm with .750 reach.

Randall Young provided he usual thorough explanation:

For almost any given brand of plug, the letters determine all the plug physical dimensions, while the number is the heat range. Unfortunately they differ between brands as to whether a higher number is hotter or colder. For Champion, higher numbers are hotter. The Champion chart I have lists the following plugs, in order from hottest to coolest :

RN16YC5
RN14YC
R/N12YC
R/N11YC
R/N9YC
R/N7YC
R/N6YC
RN4YC

The trailing 'C' indicates Champions "Copper Plus" line of plugs, which replaced the 'standard' N9Y. The leading 'R' indicates an internal resistor, for EMI suppression (and where I've written R/N it means the plug is available both ways). Randall also shared a good site at NGK about plugs. http://www.ngksparkplugs.com/techinfo/spark_plugs/techtips.asp