Im reading what PEOPLE do to their cars, not Sport Compact car and Import Tuner. EvoXforums has an abundance of information. Taking the cat out screws with the A/F parameters, with or without the AMS CEL delete, thus the NEED for a retune/reflash.
However, it can be boosted safely to 25 psi as long as there is more air in and out. I’ve been reading and reading and reading. I’m doing this right guys.