I am rebuilding the 5.4 out of my 99 F-150 and had the machine shop doing my work install Full-Torque spark plug inserts in all 8 locations. I have to switch to a full length threaded spark plug and am having a hard time finding someone, even at the dealership, who can recommend a spark plug that will have a temperature range close to what the stock plug had, but in a full length thread. Anybody with inserts have a recommendation on plugs? Just for kicks, here is a pic of my baby so far (headers attached for dramatic effect).

 

Those headers look like crap, don't embarrass yourself. You should take them off, go ahead and send them to me ,I will discard of them for you. ;-)

 

What do you mean full length threaded spark plug? Any of the new Motorcrafts should have threads all the way down, SP479.

Nice looking engine though!

 

As nice as that is of you, the best I could do is to send you my old manifolds, they look almost as bad.

Ahhhh....I see, and now I feel like a dumbass. My old plugs were only partially threaded, so I assumed that those were still standard. Thanks a bunch for your help.

 

No problem. I understand the confusion, those were the originals I would guess. Good idea with the inserts right away. Those and new gaskets should make that engine run for a long time.

 

I have rebuilt the motor from top to bottom and had it balanced as well as adding the goodies shown. I spun the #4 rod bearing and figured while I was there I might as well go all the way and prevent a spark plug catastrophe.
Thanks again for the help.

 

Ngk iridium ix are one of the best plugs I have ever used in the modulars.