Test pipes is just piping welded to the headers(or bolted if you weld flanges to the pipes like i did) to delete the cats. HFC are still legal but still restrict some power as to where test pipes restrict none. Kinda smelly though on my car since its got test pipes. Smog check is not really a big deal where i live. Thats really the main difference.

Buy a different car. There isn't much worth the money for performance parts for this car. Its a fun car but not one to start slapping parts on. Save your money.

So you want more performance. First get a better exhaust setup headers and all. Allowing more exhaust gasses to flow increases horsepower and torque. Intakes if you get a good one will free up a few ponies (maybe 5 or 6 if you're lucky) but, an intake isn't just about more horsepower. They allow more air to flow into your engine with less travel and less restrictions while freeing up a few ponies although you'll never feel 5 or 6 horses. If you have an automatic, get a transgo shift kit, it will do a world of good for your tranny but, if you have a 6mt, get a stage 2 or stage 3 clutch with a light weight flywheel and one piece aluminum drive shaft (carbon fiber isn't necessary). A nice set of lowering springs and swaybars will help you corner like nobody's business but, replace the stock struts and shocks with Tokico. Everybody will say get coilovers but, unless you're going to the track than a good set of lowering springs will work wonders. A quaife rearend differential will help put the power to the ground better and a finned rear diff cover will help keep the temperature down. If you haven't done so already. Switch to synthetics in everything. Oil, transmission, and rear differential. A Koyo radiator will help bring the engine temperature down and a strut tower brace will help stiffen the front end.

A set of intake and exhaust cams will help free up quite a few more ponies along with a tune. Building the motor with stronger pistons, cams, valve springs and retainers, a port and polish of the heads, and stronger connecting rods will give a monster of an engine. Forced induction will also put your power way over the top. A short shift kit will help as well along with a better grounding kit. Light weight pullies will free up more ponies too. A nice set of 20's will fill the wheel wells nicely. A big break kit will help shorten those stopping distances along with brake fluid that has a higher boiling point, along with stainless steel brake lines. A finned oil pan will help keep oil temps down and aid with cooling the oil.

^opinion < facts

^ more facts than you know

Whats the HP gain difference from HFC to Test pipes being on the sedan I have a 07 sedan.

Also what is the sound difference?