6 is the stock heat range. 7 is one colder and from what I heard is better to use with turbo. If n/a then go one range hotter - 5s. That is what I run and works great. NAPA part number is 6953 for NGK V-powers.
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1999 Eclipse RS
ET: 16.1 @86.241 | Speedworld Motorplex, Phoenix, AZ