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I tune the engine on BKR7, then install a fresh clean set and drive the vehicle 5k miles or so to review the plug condition in it's final tuned state. Then always switch to Iridium, usually heat range 7 , BKR7EIX for example. This for 2jz, sr20, or even LS application, pump gas, up to around 125hp/cyl, try to keep the gap open .021" to .025", doing this for around 20 years hundreds of cars
In LS application I use the TR6 or TR7 NGK plug for tuning as above (part# 4177 = TR6)
Then switch to iridium version of that plug with stock coils for up to 1200rwhp using stock engine 05-07 L33 5.3L for example, gap .019" to .023" , D585 coils , Heat range 7 or 8
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