Can someone explain the real world difference in engine operation using the different heat range spark plugs. How and when would you know which heat range your particular engine is wanting?

real world, if you put a bpr8 in a stock Z engine it will foul badly, because combustion isn't hot enough to get the plug hot enough to self clean.
if you put a bpr6 is a high compression tuned engine, the tip of the plug will melt because combustion is too hot.
the right plug for the engine is one that doesn't foul and doesn't melt.

4 hours ago, torynich said:

 How and when would you know which heat range your particular engine is wanting?

AS jonbill describes, it's not what your engine wants but what will survive and stay clean in the engine.  The engine will run exactly the same until the plug fouls or burns up.

So it sounds to me like the answer to the question is "Use the coldest plug you can that stays clean."

Would that be accurate?

So it sounds to me like the answer to the question is "Use the coldest plug you can that stays clean."
Would that be accurate?

yes, or the hottest plug you can that doesn't melt.

Or the medium plug that’s just right


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Got it!    

Thanks everyone ?

Kinda reminds me of Goldilocks and the three bears..

This porridge is too hot!" she exclaimed.

So, she tasted the porridge from the second bowl.

"This porridge is too cold," she said.

So, she tasted the last bowl of porridge.

"Ahhh, this porridge is just right," she said happily and she ate it all up.


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Then she went over to the three little pigs house, blew it down, and ate grandma.  I remember those stories...