I replaced my factory plugs with NGK Iridium last Fall. What can I say, they work fine so far. Nothing good, or bad that I can tell, but I only have about 8k miles on them. However, I believe they still have a nickle ground so I would not use them in a 4.6L without making sure. No sense using a $9 plug if it isn't any better than a $0.99 one.