I have an 05 cobalt with a 2.2 and i am going to have a pretty good turbo build soon. I am going with a zzp stage 3 changing rods and pistons and all that stuff. Will a magnaflow exhaust with a 2.25 in diameter be enough flow for this turbo setup.

 

no!
the least i would go is a 2.5" make sure its INNER DIAMETER.
if you're gonna have well over 250 horses though get 3"

 

2.25 would be good only if you were remaining N/A.

Since you doing all the internals, you can really crank up the boost and the power. I would also say go for 3", or atleast 2.75" at a minimum.