That is strange. Also went to the Denso site, and their 5018 QJ16HR-U Nickel Spark Plug shows up for the Special. Went to Amazon, tried DENSO Iridium Spark Plugs IK16 # 5303, and it shows a fit for the car.
Sure enough, checking the specs for both Denso plugs, they are the same, the gap the only difference in specs,.32 for 5018, .44 for the Iridium. Same heat range(16), threads, reach, ect.
Wonder why Denso does not have their Iridium plug pop up for the 3.5 Special on their website?
Some have said some engines do better with a Platinum plug, or even copper. Isn't Iridium a harder material than all of them? I'm sure not a spark plug expert, but get the hardest, smallest electrode in the preferred heat range?
The NGK 7781 Platinum plugs also have identical specs, except the gap at .050. Their NGK heat range shows up as a 5 for the 7781.
Last edited by Dave2004; 01-21-2014 at 09:20 AM.