![Grapje/Razz :P](./images/smilies/icon_razz.gif)
http://www.ngksparkplugs.com/techinfo/s ... 0&country=
"........ it says plugs have two functions - to ignite the
air/fuel mixture and to COOL the combustion chamber. One
grade cooler ( 7 instead of 6 ) will mean 70 to 100 degrees
drop in combustion temperture!!!! "