Since I see lots of reference to "one step colder" with no reference to part numbers, I wanted to point out that on the BMS website it's all relative to the stock N54 plugs.
So the: "NGK 5992 1-Step Colder Spark Plug" is actually the same heat range as the stock N55 ZR5TPP33S plug.
One step colder would be the NGK 97506 N20 replacement ones.
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