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Can anyone confirm if this spark plug heat range cross-reference chart I found seems accurate or not.
In my supercharged '79 I had been running NGK BR8ES plugs in my car and recently switched to Bosch. I thought the heat range for a Bosch plug in a standard 928 was a 7. Being supercharged, I went 1 range colder to a 6. Bosch #s get colder with the lower numbers whereas NGK plugs get colder as the number increases. With a Bosch 7 I though I was comparable to the previous NGK 8,but according to this chart, I'd need to be in a Bosch 4.
I don't think I've ever run this cold a plug in any of my cars.
If others (Eric, Dave, Carl, etc) have recommendations for my setup, I'm open to those as well