2000 NB California emission vehicle compared to 49 state same car?
 

Wife recently purchased a 2000 5 speed. It's a nice "deluxe" performance package, or whatever it was called at the time. It's also a California car. The exhaust manifold has a primary cat, and there appears to be a second cat on the mid pipe. Getting a DTC code 421, so I'm going to try to narrow down the culprit. However, if the problem is indeed with one of the cats, they are very expensive to replace.

If one were to change to a 49 state exhaust manifold, would there be any tuning issues, check engine lights, etc?

She is also interested in a streetable aftermarket exhaust; on that gives a better sound, a bit of pep, but keep the noise reasonable. Car will never have a power adder.

It's been 10 years since I tinkered with Miatas, so I have no idea what's out there anymore.

Ca car also has another o2 sensor after the first cat, so you will have a cel if you put a normal exhaust manifold or a 01-05 manifold.

I remember 2 O2 sensors on my non-Cali Miata; I assumed even a Cali car would have only 2.

Both the CA car and the Federal car have 2 oxygen sensors. The CA car has the front one in the exhaust manifold and the rear one in the downpipe. The Federal one has the front one in the downpipe (very close to where the CA rear one is, I think) and the rear one in the midpipe, behind the main cat.

Racing Beat used to sell a kit to relocate the rear oxygen sensor on a 99/00 CA car to the Federal car rear location. It's basically a bung (there isn't one on the CA midpipe, so you need to drill/weld) and a 4 foot wiring harness extension with the right connectors on it.

--Ian