To make power out of a 4afe.
How much u got?
cheaper mods include cold air intake, better flowing exhaust (not like the fe head can allow good flow anyway at higher revs).
Bit more $$$ and you could afford a very rungi turbo setup, nitrious.
and when you get a bit more $$$ you could replace everything to parts willing for boost (forgies etc), and a rather large turbo off the side, along with a new ecu

.
my suggestion for bang for buck. Nos.