copper or iridium plugs for KB?

[Bundmar]

Which Spark Plugs to use with my KB 9PSI Intercooled, Kenne bell says should use the NGK Iridium plugs, but a local shop is saying to go with the Copper plugs from motorcraft.
which should I go with?

 

[Kilgore Trout]

I would go with what KB says...

 

[tl75keith]

NGK-TR6 gapped at 35.

 

[tooblue02]

Autolight Ar-94's

 

[misterb]

Which Spark Plugs to use with my KB 9PSI Intercooled, Kenne bell says should use the NGK Iridium plugs, but a local shop is saying to go with the Copper plugs from motorcraft.
which should I go with?

The stock heat range (for Denso) is IT-16, one step colder is IT-20

The stock heat range (for NGK) is TR55-IX, one step colder is TR6-IX

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