you can tell by how the plug looks also If i recall correctly. when I had my '89 Vette and was tuning the plugs I was using a Scanner that counted "knock counts". I ended up going with a NGK V groove 2 steps colder.. probly could have gone colder, but stopped testing there. You wanna go as cold as you can until it fouls up, then 1 hotter. you wanna be 1 heat range from fouling. but for most daily driven applications 1 or 2 steps colder is fine.

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