My car developed an exhaust leak, and after looking at it, it's in the front catalytic converter pipe. The 2010-13 Mazda 3 uses a one-piece exhaust manifold/cat pipe that goes all the way down to the mid-pipe.
Mine seems to have rotted right after the flex pipe. Thanks, New England. 
So far, there's no CEL, which is baffling, but I should replace it soon.
Here's the problem: The part itself is not available locally, and since my car has California Emissions, it's extra hard to find. And since it has cats, most places cut the part I need off and just sell the manifold. From the dealer, it's a staggering $900 plus tax. I have no idea what's different between the Federal and California Emissions pipes, but they look 100% identical.
Take a look for yourself.
Federal:
California:
Could I theoretically replace the one on my car with a Federal Emissions one without the car freaking out, or am I screwed?
It could be the stamp/label that is the difference. I think they have to pay California a fee for each one sold with California certification. So they only certify as many as needed and charge accordingly.
It's also possible the cat itself is slightly different.
It looks like the CA emissions one has an extra sensor (O2? EGT?) pre-cat.
There appear to be a variety of aftermarket options on ebay for $200-400
The bung appears to be there on the Federal variant you zoom in, just no sensor installed.
I think the tune is different (at least it is with the MS3 while being identical with emissions parts) beyond that I'm not much help.
Alfadriver or Keith would be the expert here.
To answer a few questions:
-Both the Fed and CA pipes have two O2 sensors: one at the manifold and one past the flex joint. To me, they look exactly the same.
-I've found aftermarket ones, but they are all for Fed Emissions cars. There's an OBX header and pipe, but it has zero O2 bungs so it's useless. There's also a Magnaflow one, but all the pics are of CAD drawings and it costs $700 and is for Fed only. There are zero aftermarket CA Emissions options.
If this was a MS3, there are a million options for reasonable money. It's annoying.
Couldn't you have a shop weld in a set of O2 bungs in the appropriate locations on the bungless (heh heh) aftermarket part?
02Pilot
SuperDork
11/21/18 8:46 p.m.
If it were me I'd be inclined to just get the Fed-compliant one and go with it. I doubt the ECU will know the difference as long as it gets the proper sensor inputs, and I've never heard of anyone looking for a CARB tag anywhere outside of CA. Hell, let it rust in place for a few months and no one in the NE will guess it's anything but factory.
