Ok, I see. The life of the spark plug itself is going to be the main factor here, if I use these plugs (6702) I'll just be back under the hood sooner than later. From a little more reading into the subject it seems like they will deliver the same performance just have a shorter life span.

@ Can't Know - what do you mean by conversion number?

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500