A Mustang's Catalytic Converters – The Basics
Catalytic converters have been equipped on all new cars in the United States since the 1975 model year to comply with U.S. Environmental Protection Agency regulations on automobile exhaust emissions. Their purpose is to convert the toxic byproducts of the internal combustion engine--exhaust gases--into less toxic substances by way of a catalyzed chemical reaction for release back into the atmosphere. Catalytic converters or “cats” look like small mufflers and are normally located directly after the exhaust manifolds (a.k.a. headers).
Mustang Catted Mid-Pipes – Street Use
As you may have guessed by now, a catted mid-pipe is one that includes catalytic converters. These are ideal for use on street vehicles that require the use of catalytic converters by law; you will need to check your own local and state ordinances for exact regulations.
In general, most aftermarket catted mid-pipes feature high flow catalytic converters that provide a significant increase in horsepower and torque over the restrictive stock factory cats, but still remain emission legal.
Mustang Off-Road Mid-Pipes – Track/Race Use
Off-road mid-pipes do not include catalytic converters and are intended for off-road use only by the manufacturer. By removing the restrictive factory catalytic converters from the exhaust, the vehicle is able to produce more horsepower and torque, making them perfect for race applications such as track and drag racing.
They are not for use on street vehicles that require the use of catalytic converters by law; you will need to check your own local and state ordinances for exact regulations.
Mustang Off-Road Mid-Pipe Accessories
Because an off-road mid-pipe eliminates the catalytic converters from the exhaust equation, the rear O2 sensors will read too much CO2 and throw a code with an annoying check engine light. There are two ways to turn off the light (this does not stop the code from generating; it only turns off the light): MIL Eliminators are the easiest way to solve this problem for the 1996 to 2004 Mustangs. MIL, which is short for Malfunction Indicator Light Eliminator, plugs in between the rear O2 sensor and the harness to block the codes generated by the rear O2 sensors. The other alternative is to use a handheld Tuner, is to load a custom tune and turn off the check engine light.
Avoid a catastrophe, make the right purchase
When making your mid-pipe purchase, you need to ask yourself a couple of questions. Do I live in an emission restrictive state and how will I be operating this vehicle? When in doubt, it’s always best to err on the side of caution and purchase the catted version. However, if you know your local laws permit cat-delete exhausts or you’ll be using this car for off-road use only, get rid of those restrictive stock factory cats for more power.