muffler bypass - pointless!

No change in sound. Mine is a 96. John

Aren't cats under Federal jurisdiction?

No idea. Maybe it depends on the year of manufacture. I know that here we have safety inspections and we're allowed to switch to larger exhausts minus the cats

Yes, it's a federal requirement. State doesn't have a requirement, because the feds already do. Removal or modification of the cat carries a $10K fine.

Incorrect statement Sir. Cats are required by Federal law on ALL vehicles produced after the mid '70s or these about (IIRC). Just because a certain state, AZ (in places here) for example, do not conduct emissions testing, does not allow one to "legally" remove or otherwise alter your cats.

Emissions regulations vary considerably from jurisdiction to jurisdiction, as do what engines are regulated. In North America any spark ignition engine of over 19 kW (25 hp) power output built later than January 1, 2004 probably has a three-way catalytic converter installed. Diesel engine regulations are similarly varied, with some jurisdictions focusing on NOx (Nitric Oxide and Nitrogen Dioxide) emissions and others focusing on particulate (soot) emissions.

Diesel Engines For compression ignition (i.e., Diesel) engines, the most commonly used catalytic converter is the diesel oxidation catalyst. The catalyst uses excess O2 (oxygen) in the exhaust gas stream to oxidize CO (Carbon Monoxide) to CO2 (Carbon Dioxide) and HC (hydrocarbons) to H2O (water) and CO2. These converters often reach 90% effectiveness, virtually eliminating diesel odor and helping to reduce visible particulates (soot), however they are incapable of reducing NOx as chemical reactions always occur in the simplest possible way, and the existing O2 in the exhaust gas stream would react first.

To reduce NOx on a compression ignition engine it is necessary to change the exhaust gas - two main technologies are used for this - selective catalytic reduction (SCR) and NOx (NOx) traps (or NOx Adsorbers).

Another issue for diesel engines is particulate (soot). This can be controlled by a soot trap or diesel particulate filter (DPF), as catalytic converters are unable to affect elemental carbon (however they will remove up to 90% of the soluble organic fraction). A clogging soot filter creates a lot of back pressure decreasing engine performance. However, once clogged, the filter goes through a regeneration cycle where diesel fuel is injected directly into the exhaust stream and the soot is burned off. After the soot has been burned off the regeneration cycle stops and injection of diesel fuel stops. This regeneration cycle will not affect performance of the engine.

All major diesel engine manufacturers in the USA (Ford, Caterpillar, Cummins, Volvo, MMC) starting January 1, 2007 are required to have a catalytic converter and a soot filter inline, as per a new DoT legislation.[citation needed]