An exhaust alone won't do much for power anyways, especially without a tune. It's illegal to run catless, and you'll actually lose power if the O2 codes aren't erased from the ECM/PCM. But if it's sound you want, go with what was stated above, best bang-for-the-buck I'm sure.
agreed sir. Catalytic Converters are not horsepower gobblers. The only reason to not have a cat converter is if your car is exempt from emissions (race setup only) and you pulled out the entire EVAP system.
For the 02 sensors, your car will be in limp home mode, in which a p0420 code will generate (catalyst efficiency). Your car defaults to open loop status, making your car dump more fuel and pull in more air. The only problem to this, is that your ECT (Engine Coolant temp sensor) will read a default below normal operating temperature, causing the engine efficiency not to be at its peak of performance and fuel efficiency.
This will also cause problems for your emissions, ever hear people say "that car is running rich" with a smell of fuel out the exhaust pipe? That is nothing more than excessive hydrocarbons (fuel) not being broken down in the cat converter or lack of a cat. This will eventually lead down to a mechanical misfire in the engine after time, your PCM relies on air/fuel control from the rear 02 sensor heavily on STFT and LTFT (short and long term fuel trim). Im not gonna explain that stuff cause there's a lot to it. So, if your car is running rich, your PCM is trying to increase more air to balance the ratio correctly, but no cat, no go. If you think a wideband would be a solution, dead wrong. Wideband is the front 02 before the cat (just a tip to remember in the future).
2009 Cobalt LS XFE U74
Mods: K&N Typhoon Intake, Option Cat-Back Exhaust, Cosmo Short shifter, Maxxim Ahead 17X7's, MPx shorty antenna, FE5 Strut/shocks, Tein S Techs, Moog endlinks, Moog spring seaters, ZZP shorty header, LSJ downpipe, LNF front grille
Last edited by 5t3alth; 10-20-2013 at 06:12 AM.