[AtomicLabMonkey]

Originally Posted by cody

I can tell you that it's against federal law to tamper with any of your cats. I think after your car has somthing like 60K miles, you can replace the cats with new ones if they've gone bad.

From Dynomax's website:

In August 1986, the U.S. Environmental Protection Agency (EPA) issued new proposed guidelines for the construction, efficiency, and installation of aftermarket converters. The EPA guidelines state that replacement converters may be installed only in the following situations:

1. The vehicle is missing a converter.
2. The state or local inspection program has determined that the existing converter needs replacement.
3. The vehicle has exceeded the age or mileage conditions of the original equipment catalytic converter. Consult vehicle owner’s manual or emissions warranty manual for specific details on your vehicle. Additionally, a legitimate need for replacement has been established and documented.

The installer must include the customer’s name, address, and the make, model, year, and mileage of the vehicle on the service invoice, along with a stated reason for replacement. Where a state or local government has determined that a converter is damaged or needs replacement, the service or repair facility must retain a copy of the written statement or order by a proper government representative which indicated that the converter should be replaced and attach it to the invoice. Where the replacement need has not been verified by a proper state or local government representative, the customer and a representative of the service or repair facility must sign a statement verifying that replacement is justified. That statement is included in every Walker converter carton. Furthermore, the EPA has issued the following installation requirements:

1. The converter be installed in one of the three situations outlined above.
2. The converter be installed in the same location as the original converter.
3. The converter be the same type as the original converter (i.e. oxidation, three-way, or three-way plus oxidation).
4. The converter be the proper one for the vehicle application as determined and specified by the manufacturer.
5. The converter be connected properly to any existing air injection components on the vehicle.
6. The converter be installed with any other required converters for a particular application.
7. The converter be accompanied by a warranty information card to be filled out by the installer.
8. Federal law prohibits removal or replacement of properly functioning O.E. catalytic converters.
9. Not for installation or use on 1996 and newer vehicles.