There are two types of smog-legal catalytic converters—49-state and 50-state legal. In case you’re wondering, that 50th state is California. Many 50-state legal converters have a CARB E.O number and can be used in any state that abides by CARB emissions standards. The California Air Resources Board (CARB) led the way with sweeping emissions reform and the rest of the USA is gradually following suit. A replacement part or accessory that meets these standards is issued an E.O number that is supplied on a sticker or attached metal tag. Also, there’s no point to installing a replacement catalytic converter if you can’t use it in your state, so know the emissions laws in your area and what type of cat you’re allowed to use.
When it comes to installation, 50-state legal catalytic converters have an edge over 49-state legal converters, since they generally come with pre-welded tubing and flanges. This lets you un-bolt the bad converter, bolt-up the new one and hit the road with minimal hassle. On the other end of the spectrum, 49-state converters are more affordable but often require additional welding to install.