I'm gonna suggest a different direction. While an exhaust and cold air intake (CAI) will help ya out a good deal. I'd suggest a good set of tires and a bigger/stiffer rear sway bay. Something like a 19 MM bar. I like my ALTA, but I'm also liking the new NM stuff, though it's pricey.
Our little cars make pretty good power, but suspension mods make you FEEL the car work more than go fast mods do. Just my opinion.
+1!
First mod: ditch the run flats and get something sticky in 205/50/r16. (get an emergency kit from slime or conti just in case).
Second mod: do the front camber mod (pull the locating screw/pin and push the front struts inward to their limit.
Third mod: 19mm swaybar. I personally like the H-Sport for the greaseable bushings (use Teflon tape on the bar also).
Assuming the 07 in question is an MCS due to heat shield question. I would only drop coin on a shield if my scoop were to melt. If it is an MCS an inter-cooler (I like the Forge) will make some real/measurable power. Next might be an ECU tune. I'd be careful about the Alta AccessPort, some love it, some hate it. I drove an MCSa with an AP tune and it was a peaky, laggy mess, the auto shift point tuning was terrible but I hear they have been working hard to sort it out. The gas mileage was noticeably worse.
In my opinion intakes and exhaust are more about sound than power but you will find those that swear by them. For a free sound upgrade take your boot lid out to hear your stock exhaust more. Also consider doing the noisemaker delete to get a more subtle, smoother intake note.
The stock brakes on an S are actually pretty good - have you changed out your fluid?
The JCW kit is worth a consideration, the badges by themselves add power!
Always be leery of "ModGoggles" and approach all recommendations with healthy skepticism. YMMV.
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