What are the best kind of spark plugs for a 1989 F150 with a 5.8L V-8?

 

factory plugs for anything are pretty much the best you can get. but motorcraft, autolites and from what i here champions work good on these engines.

 

Stick with Motorcraft or Autolite in Ford engines as a general rule.
I've tried Champions in both 302 and 351 Windsor engines (both injected and older carbed ones) and found that they usually run better with Autolites or OEM Motorcrafts.

I know a couple guys that run NGKs in the old Windsors and they run just fine, but have never tried em myself.

 

Any quality plug will work in the older engines. I have Autolites in my 351c and they work great. I wont use Champions myself wouldnt put them in my lawnmower but there are guys who love them..