What spark plugs should I use?
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I get asked this all the time
and after seeing so many heads with plugs in them arrive at the shop
and knowing what the combo was here are my recommendations: If you drive a taxi cab or are idling in traffic for hours and hours and hours then the stock plugs are perfect. Since 99% of you reading this don't do the above I use one heat range colder in a stock engine even, and that is the Autolite 103, NGK TR6, or the Autolite AR93 which is the racing version of the 103 (cut back larger ground electrode). These plugs will work for stock to street/strip NA motors and mild blower motors. Under boost you may need to lower the gap down, but otherwise I would leave the gap as is. Most people damage the plugs playing with the gap so much and unless you are getting spark blow out under boost I have never seen a different gap make more power on these motors. Radical NA, heavy nitrous (150 shot or larger) I would run the next colder plug which is an Autolite AR92. This is different from the NGK BR7EF in that it is colder but also keeps the electrode protruding into the chamber. If you overheat the AR92 then at that point I would go to the NGK BR7EF plug. You want to run the coldest plug possible that does not foul, and with the high energy ignition capability of the stock system combined with the closed loop fueling it will take quite a bit to foul colder plugs. Start colder, and then go hotter if you have a radical combo. IMPORTANT NOTE!! If you have full thread Timeserts installed in your heads you have no choice but to run the colder plugs like the 103, TR6, etc. The stock plugs are only half threaded and will never reach the chamber with the Timeserts.!
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