Did it on my 15 st3. If you’re not doing it before the cats, all you’re doing is making noise. With my cracks and pops tune and the cutout partially open it sounds good, but at wide open throttle it sounds like ass like any no cat no muffler exhaust does on a 4cyl. On a 6 which typically sound like ass from the factory, I had zero doubts a cutout will sound like dog shit and not make any gains on the dyno that aren’t within margin of error