I have a stock 04 WRX and am replacing the spark plugs in the next few days. I have been given 3 different options for plugs; regular NGK's, platinum NGK's, or Denso Iridium's. the Denso's i bought say 0.4mm. Can you gap iridium plugs or are the pre set? .4mm seems a little big of a gap to me and I'm debating on just having the platinum's ordered instead.
the first plugs I bought were the NGK's for the 2.5 non turbo...would those have hurt my engine?