I bought a 2011 v6 mustang January of this year. It came with a few mods including cold air intake, 3.73 gears and axleback exhaust. It also came with a tsx tuner that uses the itsx app. At the time I knew very little about mods/tuning and just wanted a daily driver that looked nice. When i go into the app it doesn’t give me an option to retune, only switch between 87 and 93 octane tunes. I’m not sure if the car has a custom tune right now specifically for the mods I listed or if it’s on a preset tune.
My question is what would happen if i started adding more mods but didn’t retune? I want to add long tube headers but multiple sources say it’s bad to add mods after a tune and then not retune. Is this true? If so, how do I retune, or do i have to shell out $400 again for a new custom tune?