read my post in this thread....
zerothread/288641
sedans get more hp (supposedly) from the stillen cold air intake and z-tube combo than the pop charger.
the spacer - not that noticable but cheap and easy to install. just get it with the cai and z-tube and install them all together.
stillen exhaust gen 2 - AWESOME! pricey but, by far, the most hp gain.
unorthodox racing pulley - NICE!!!! changes the way the car drives immensely.
ground wire kit - eh. the ecu wires help it shift and (supposedly) adds hp.