Gen 3 spark plug debate??!

[mustang88_cars]

I have read plenty of information in regardes to older Gen 3 coyotes coming with heat range 7 plugs from the factory then Ford changing to heat range 6 plugs after 2021 and making it a backwards to 2018 recommendation

So what’s the consensus? Use the heat range 6 SP-589 or the heat range 7 sp-548?

For context I purchased an 85 Mustang GT Gen 3 coyote swapped car with a CAI, IMRC lockouts, and BBK long tubes. It wasn’t tuned very well if at all. I got it tuned and just want to change the plugs for peace of mind after running the car on that crappy tune.

Obligatory pics

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[cbrtrx]

The 7's still work great for NA.

 

[Optimum Performance]

The 548's will work but the 589's are what is in G3 Coyotes due to the potential for higher combustion temperatures with DI and compression. Not really certain how different they are in actual heat range. Information is spotty.

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