The ZZP header kit looks pretty good, Bit expensive, but its not impossible. I noticed some additional O2 options like a rear bung on the catless downpipe and one for a wideband gauge, would either of these options correct the O2 sensor issues or will i have to call in for the 200 cell? Also whats the difference between the 200 and 400 cell besides cost?
You'll also have the option of adding an extra bung for a wideband O2 sensor, which is basically just for tuning. Get it if you want, but it's optional.
The 200 cell cat is a less dense catalytic converter. This means that it allows more airflow, but also does less to clean the exhaust. Since it's so high flowing, it's actually out of spec for the Cobalt's computer, and thus throws a Check Engine Light. Luckily, this doesn't cause any problems, and doesn't put the car into "limp mode" but if you want to avoid it entirely without getting a tune, get the 400 cell cat. It's a bit more dense, so less airflow, slightly less horsepower gain, but it's within spec for the computer and won't throw a CEL.
If you get the catless downpipe, it will definitely throw a CEL, since that's completely getting rid of the emissions system. Also, that makes your vehicle no longer road legal. The 200 cell cat gives the most horsepower gain while remaining legal (unless you're in California, in which case you need the California cat). Since the CEL is related to the cat, none of those options will prevent it.
The only way to get the 200 cell cat is to email them just before and after you place your order. Be sure to ask nicely!
It would be about $30 cheaper if you wanted to buy the ZZP shorty header and 2.2L downpipe. These are essentially the same lengths as stock, although they're definitely more high flowing. The shorty and midlength headers add power in different RPM ranges, so do a bit of research and figure out where you want the power.
Edit: The K&N short ram kit is a bit pricey, Are there any other alternatives for SRI?
There's an Injen short ram intake, but I think it's more expensive. ZZP has a "high flow 2.2L intake tube" that is essentially a short ram intake. Get that and a drop in K&N filter and you'd essentially have a short ram intake with the stock airbox filter. If you do that, consider removing the "air silencer." There should be a thread somewhere on how to do it. If you don't want to remove the bumper, you can use a hacksaw to remove one of the plastic mounting arms.
You could also look around for a used K&N or Injen.
ZZP Midlength Header & Downpipe
ZZP Shorty Header
ZZP 2.5" Downpipe (Fits on Shorty or stock Header)
You could also get the 3" downpipe
, but if you're not Turbo/Supercharging, you don't need it.
ZZP High Flow Intake Tube
K&N Drop In Filter