Here is a list of "stock" plugs that work in the srt6, just increase the number on the heat range to order a colder plug

http://sparkplugs.com/results_app.as...1&AAIA=1431386

this should help you see how to pick a hotter or colder plug:



the higher the number the colder the plug, if your stock plug was pfr6a-11a and you wanted 2 steps colder then you would get a pfr8a-11a