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Fritz zozobrado
Going to assume you're talking about for a naturally aspirated (non supercharged/turbocharged car) with a tune. So, after upgrading to a catless header (like you have), you're not going to see much for gains with the other parts (especially for a DD car that is NA). So choice will come down to budget, pipe diameter, aesthetics, sound, materials and build quality.
Header - UEL Tomei - catless - Gain + 7 -10 WHP NA on 91-93 octane pump gas.
Overpipe - Any aftermarket - Gain + 1-2 WHP NA on 91-93 octane pump gas.
Frontpipe - Any aftermarket (If catless, then recommend resonated to cut down on noise/drone) - Gain + 5 WHP if catless on 91-93 octane pump gas.
Mid-pipe - Stock midpipe or the midpipe that comes with a catback exhaust system - Gain + 1 - 4 WHP NA on 91-93 octane pump gas.
Muffler - Any aftermarket
axleback if using stock midpipe
or any aftermarket
catback exhaust system. Also you may choose dual or single exit. Single exits are usually quite a bit lighter. - Gain + 1 - 4 WHP NA on 91-93 octane pump gas.
That's about it.
