Seems that a pi swap is a fairly common/popular mod. I haven't posted much but have been lurking here for quite a while trying to glean as much info as I can. I think I get the jist of what a pi swap is, but what does the 'pi' stand for. I'm an ex military man and we had tons of acrynyms and abbrevaitions. But I like to know what they all stand for. Thanks in advance.
"The 03 is stronger because starting in 99 ford mage the sohc motors with the "power improved" setup, which entails different shaped ports in the heads, a little higher compression, different grind cams, and a manifold with different shaped ports, that's what makes the difference, and the reason people with pre-99's do the PI swap." -racin366
and also
"PI = Power Improved
nPI = non Power Improved
The nPI heads can be found on every 4.6L car from 92-98, although the pre OBD-II heads and engine design vary slightly from year to year.
The PI heads are little different because the 5.0 stayed in the SUVs for quite a while and I don't think it was until 2002 that they got the 4.6L SOHC, but when they did it was PI. I really couldn't tell you when the Panther bodies went PI, but I'm sure someone else can fill you in on that. The Mustang GT was PI from 99-04. There was two main PI castings, the Romeo and the Windsor. You can Identify them by the amount of valve cover bolts, among other things.
Of course, this is only speaking of 4.6L SOHC engines. If you have any questions about any other differences I would suggest the search function because this topic has been covered many times before." -Dave Mustang
So this is why the PI swap is done. Glad I have a 99 GT haha.
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99 mustang GT
Vortech V-1 Supercharger, 42lb injectors, Sean Hyland Blower Cams, JBA shorty headers, Mac O/r H pipe, Mac High Flow Cats, 373 gears, spec stage 3 clutch,75mm TB, Bullit Brake Upgrade, Bullit rims, 90mm MAF, Steeda Boost Pipe, Steeda Tuned, CNL Plenum, Steeda Springs, Tokico Gas Shocks
Awesome, good luck with the swap, be careful/meticulous when you install the cams, its pretty common to get them off a tooth and then it'll run like doodoo.
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That hunk of junk? Yeah, well I've made a few special modifications to that yellow 99 Gt, it makes the Kessel run in 12 parsecs and eats turbo japs and poops chevy's
PI swap in progress 
