i got a 08 taffy white 4dr si bought a few months ago and bought hfp lip kit and other outside looks but know i wanna go with performance. my question is which exaust system,headers and intake would give me da most performance?
Best performance mod is suspension, brakes, wheels and tires. The word 'performance' is not equivocal to speed.
For speed, exhaust and header are the best places to start; the exhaust system will always be needing an upgrade whether your ride stays naturally-aspirated (NA), or forced induction: supercharged or turbo charged (FI). A port-matched and polished intake manifold would be an expensive but good option for NA, as well as lighter weight pulleys. Other engine mods (like cams) are limited by a lack of tuning (i.e., electronic control; fuel, timing, ignition, and cam angle adjustments for optimum engine performance.)
It's been debated here whether an intake provides gains over a throttle body spacer or plenum for more air volume before compression. Evidence points that a spacer may be best over an intake.