the cat flows differently meow.
And don’t forget to replace intercooler hose that usually blows out stage 2 or is that different with 2.0’s??There will be less back pressure on the turbine, which will in turn make the turbo work more efficiently. I haven't really looked into exactly how the new ECUs are set up, but the biggest issue with previous years was that the increased efficiency would allow the engine to hit load levels that simply were not tuned in the stock map. Basically, once the car got up and going it would hit a point where the computer didn't know what to tell the engine to do anymore.. bad things would happen as a result.
Not to mention that even if you didn't need tuning to prevent engine damage, you wouldn't get much power increase from the new exhaust anyways. The modification allows for more aggressive tuning, which is where you get the performance increase.