Right now I have the Bosch 4 pronged things but I've read those are no good. Aside from Motorcraft and Autolite, NGK TR6 seems to be popular. Independent of cost, what's the best for our motors in terms of performance and reliability?

 

I roll with NGK TR55 but I am N/A and don't have many mods

 

I would think it would be safe to run a slightly colder plug...get as much spark and fire to that fuel as you can for efficiency and power.

 

I ended up going with the TR55IX's. One strange thing I noticed when installing them was how many threads there were in the heads. I had another 2004 Mach 1 prior to this one (F250 blew a stop sign ) and when I did plugs in that, I could swear it didn't take as many turns to fully seat them. I have no idea what the build date was, but did Ford change anything?

 

Motor Craft for me in my Mustangs lately.( not a Mach 1 but a 4v )

But I hear great things about NGK's TR55 in our Ponies for N\A .