Does a splitfire make a big enough difference to change to one? If so does anyone know where I can get one for a 95 Explorer or 00 Trail Boss?

 

NGK has a good explanation of the function, purpose, capabilities and limitations of "multiple-ground" (e.g., "Splitfire") plugs in the FAQ section of their website (NGK makes "multiple-ground" plugs also).

Tree Farmer

 

I'll agree with that Tree Farmer, it pretty much tells it like it is. Very informative site.