ngk tr6 are the wrong plug for ur car. they are one stage colder which would be great if you were running nitrous, but if your not then get the right plugs. just get a set of basic copper plugs for 2$ a piece at advance/auto zone. i personally am not a fan of autolite plugs. NGK makes descent plugs and they have a great warranty.
i actually have the NGK TR-6 plugs, because i had plans of using nitrous. Those plans have changed. Unless your spraying there is no need for a colder plug. The NGK V-power TR-55 is perfectly fine for our cars. They cost $2 each. The NGK TR-55GP is the platinum and is $3, pay $8 more and maybe feel better about yourself...
True that. The only thing better about the platinum ones is they last a little longer. But I don't believe they last as much longer as they cost more so I've always staid copper. If you go FI or Nitrous or something a step colder is good, but still don't NEED to get anything better than tr55's for less than about 500 hp.
I read reviews on a bunch of spark plugs a long time ago. They basically said tr55's are the best bang for your buck and performance wise, its still ahrd to get better even when you spend a LOT of money on them.
I run Autlite's AR series plugs. The copper plug is actually better for a performance vehicle because copper is a better conductor. The platinum plugs are designed for longevity. My old 01 GT with bolt-ons actually liked a colder plug. I used a AR 103 in that. The next step colder is a AR 94 and that's what I currently use in the Cobra.