I just recently replaced my plugs on my procharged Z. I already had 1 heat range cooler plugs from Nissan/NGK from when I was running N2O..Well anyway my plugs were BLACK..I am running real rich..Better than lean I guess..And I was suprised to see the part numbers were the same as the plugs I already had in there but the tips looked different on the ones I had...The new ones had a flat electrode as the old ones had a pointed electrode..Strange..Anyway after the winter I will go and get leaned out a bit..BUT not to much!!!

 

Hmm, are the new ones perhaps copper? The standard copper plugs do have a much larger (flatter) center electrode, and platinum is a much smaller 'point'. The NGK part numbers are the same except the platinum has 'P' prefix if I recall.

 

Thats probably what it was...But the old ones were nissan oem parts Made by NGK...@$11.67 a peice from Nissan..