Hi,
I have a buddy club pro spec exhaust on mine and a hks premium suction kit,took my car to power engineering last weekend and my car was down on power,269 bhp and 255ftlbs,they told me the ecu was over fueling and i would need to get a fuel pressure regulator,they expected a revised figure of 285bhp and 270ftlbs of tourqe,so there you go,performance mods stealing your power.
Hope this helps