Originally Posted by foleysfriend
What is the difference in the two plugs when it comes down to performance and does it effect idle quality to go to a colder plug or type of octane you can run
Colder plug = higher compression & the attendant need for higher octane fuel
Hotter plug = stock compression, stock engine, or worn out engine
If the plug reads "hot" for your combination, you'll need at least a range cooler. (The temperature of the plug is how fast if transfers heat from the tip)
As far as idle quality, colder isn't a problem as long as it isn't loading up and fouling out..... that would be a problem, as you can probably imagine.
Octane requirement is mainly a function of compression.
It's always safest to be too cold and foul plugs, than to have the plugs be
too hot and have pre-ignition/detonation issues.