I'm looking to change the plugs in my fiancee's FX, and we tend to run a combination of 87 and 89 octane fuels through it. She hasn't experienced any knocking or anything else, but I was still thinking about running a hotter plug just to aid in ignition. I am looking for either NGK or Denso Platinum or Iridium plugs in a hotter setting (if this is right for my thinking). Can someone help me out with part numbers? TIA!

OEM is the way to go...NGK plug...if the hotter plug is what you are looking for them the OEM part number is 22401-5M014 or here is the NGK number as well PLFR4A-11. They are platinum plugs and are 105,000 mile, and already pregapped. I got some from infinitipartsonline, $9.74 each.