I was in the same situation. Well technically, I still am. I have completely stock exhaust so I know where you're coming from. My girlfriend has stock mufflers and an O/R X pipe and it's pretty loud (although from my experience, x pipes are normally louder than h pipes). I was thinking of doing the same thing but instead doing it with my stock H pipe. But I wouldn't recommend it.
First of all, you never know when your state will start emissions testing, unless your state already does emissions testing. It's nice to have the stock H pipe around for when you need it, doesn't matter the occasion. Because of this reason, I would just buy an offroad X or H pipe, they're cheap and you get to keep your stock H around for when you need it. In New Orleans, there's no emissions testing but they do in Baton Rouge and in a couple of years, it'll spread here. Luckily I have a Mississippi license plate but still, you never know when your state or city/town will start emissions testing. And when that happens, you'll say "oh ****." It could be tomorrow, next month, next year, or even a decade away, but you always want to stay prepared.
Second of all, hollowing or removing the cats with the stock mufflers will sound alright and a bit louder, but it will not sound as good as a set of aftermarket mufflers and an aftermarket midpipe. Because I have stock exhaust, my girlfriend's O/R X and stock mufflers sounds better, but only because it's louder. In reality, my stock exhaust is actually better sounding overall. Hers may be louder, more throaty, and better sounding at low rpms, but when she goes WOT, it's loud but sounds NOWHERE as good as mine at WOT. Maybe it's because hers is more raspy than mine at WOT, but I've also heard the hollowed out stock H pipe and stock mufflers combo, and in my opinion, I'm really not impressed whatsoever. Louder, but doesn't sound as good to me like the stock setup, I can easily tell that all he did was hollow out the cats. He said he didn't like it like he thought he would (he said it sounded like a ****** old Chevy Truck, although maybe he was exaggerating a bit), but just wanted more sound and after a while he said he was regretting it. Like I said, a set of aftermarket mufflers (the mufflers make a huge difference) and an aftermarket midpipe will sound SO much better and it's worth the money, trust me. There's a reason why people save for their exhaust rather than just hollow out the cats or punch holes in the mufflers, it's because it's worth it.
I can always tell when a car (like a Mustang or Camaro) has hollowed/gutted cats with stock mufflers or an aftermarket exhaust system, that's how much of a difference in sound they have. The hollowed cats and stock mufflers I hear on most cars or trucks (not saying ours, but just in general) sound like crap to me. The free route just isn't worth it. Somehow, even a cheap aftermarket offroad H pipe sounds better to me than the stock cats hollowed. Don't know why.
If you want cheap and loud, go for a muffler delete like the Pypes Pype Bombs or the SLP Loudmouth. About the same price as the higher end x pipes (around $300 or so on AM) and sounds much better because it was meant to work with the stock H. And you keep your cats while still being loud so it's a win win. Unless you're like me and have an awkward gasoline smelling obsession. Then you might not be so happy. Some people complain about the smell of an offroad midpipe, but I LOVE the way it smells.
Just gotta be careful to protect the brain cells.
Okay, I'm getting off topic. Just save up your money and get an aftermarket midpipe and axle back (or catback). I'm actually at my summer job right now, saving up specifically for my exhaust setup.
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