Replacing only Y-Pipe (keeping cats)
 

Forgive my ignorance, this is my first import, I'm used to older-isn Mustangs where you had headers, a mid-pipe and a cat-back.

So on here you've got headers to mid-pipe, to y-pipe, to cat-back?

Again, just getting use to the differences and not sure what the "y-pipe" is.

On topic, I've got AAM non-resonated short tails. Love the tone but a tad too quiet for my tastes. I'm really not a fan of most of the test pipes I've heard (Art Pipes sound great but out of my budget). Got curious about replacing the Y-Pipe and leaving the catalytic section there, is this a reasonable thing to do and sound-wise what are we looking at.

I can't get a view underneath very well which is also why I'm trying to see if the Y is before or after the catalytic section, a test-pipe seems like a nightmare to install with that one bolt that's impossible to reach, how's the Y-Pipe install?

Appreciate any input. dumb question but still learning about these cars.

I can’t speak to the sound you’ll get but replacing the Y pipe is something that can be done on jack stands with hand tools in under an hour.
I don’t think the y pipe is nearly as restrictive as the cats. Have you considered high flow cats or maybe resonated test pipes?
I have the non resonated test pipes and with the stock exhaust they were a lot louder but very raspy.
Now with an added full CBE the rasp is nowhere near as noticeable but you can definitely tell the car is breathing a lot better.
Hope this helps.