one cylinder running colder than the rest.....

[Chevy454]

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Tom,
I doubt the plug heat rating will affect the combustion temp. It will affect how long it lasts before melting or fouling. I think that changing a plug heat rating in a cylinder is just a compensation for the heat of that cylinder; not a method of changing the heat in that cylinder.
JMO
Verne

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Verne: a spark plug is doing exactly that, ie, helping regulate chamber (combustion) temperature by dispersing (or not) heat...the amount dissipated has to do with insulator length. I can't remember the exact numbers off the top of my head, but the % of cylinder temp that is transfered via the spark plug is surprisingly (alarmingly!) high...over twice the amount cooled by the charge, I believe?

Stagger jetting and plenum design/alteration can help cover up the distribution problem, but I'm gonna bet Eric has some great info/numbers on this subject...