just wondering what everyone uses. stock AC-delco or NGK. and parts numbers for both.. im leaning more towards NGK, bro just installed some in his ws6 and it runs wonderful.. just wondering if it is bad to run 1step colder plugs on a stock tune? mine is stock tuned atm but geting tuned in the near furture. im at 50k miles and i doubt my plugs were ever changed by the previous owner ( a girl!) or let alone if she was using the proper 91 octane or crappy octane gas.

 

Well it seems you cant go wrong with either my ngk's (stock) lasted a solid 83000 miles. I replaced them with the Acdelcos 41-106.

 

The stock AC Delco plugs are made by NGK fyi.