That's exactly right! The part of the plug that determines heat range is the ceramic center. It doesn't stick out any further on a hotter plug, but it is deeper on the inside of the end of the plug (the ceramic firing end), and leaves more surface exposed to combustion gasses, it dissapates heat slower therefore the firing end heats up quicker. On say 1 heat range colder plug, the open end is more shallow, so there is less surface exposed to combustion gasses and dissapates heat much quicker into the head (and engines cooling system), so the firing end does not heat up quickly. A single heat range colder plug can reduce combustion chamber temps approx. 158*~212*. You are also right about the plug gap, on nitrous apps. .035" is what I always use. Here is a good link on reading plugs, very very good info and some may be surprised to find out what plug section is read for jetting, or timing, or even heat range. http://www.dragstuff.com/techarticle...ead-plugs.html

 

hog is absolutely, 100% right. Couldn't have said it any better myself, honestly.