Yes, I'm also confident that it's been discussed here on FTE. However since I've read threads in several different sections & lack perfect recall, the date when FORD introduced improved heads in Econoline eludes me.

Anybody think PI (Power Improved) heads, which have substantially more spark plug threads to combat blown plugs, were not installed beginning with '01 Econoline? What year then?

Thanks for offers trying to find far flung threads on this topic & good luck searching.