Spark Plug Heat Range Question

[fargineyesore]

I've added a pipe and port and polished the engine on my 99 Explorer. Can I still run the stock plug or should I go to a cooler plug?

 

[doobest]

You can check your o2 count, and pull a plug after a run and check it. Is you knok sensor recording a ping and setting back your timming? I would install a plug 1 heat range cooler and gap it 5 thow less than factory, this would mainly be do to the alcohal in our fuel now, the older ones like yous cant compisate enough for that.