find out what size it is, then go to a cobalt forum, manual, or in some other way find out what kind of boost your engine can hold with stock internals (assuming your not built)
likely no one is here going to be able to tell you the capabilities of your car, unless they have one and have experimented themselves.
well the inside of my motor is all stock forged from the factory. theres a company in MI making 523 corrected whp with a stage 4 clutch and bigger valves.
im looking to make like 400+whp Mike at innovative told me that turbo is good for 2xx whp, my K04 is making roughly 320-340 whp ok. so im just gonna stick with it.