This modification includes the pipes, muffler, and sometimes the resonator. The term "cat-back" itself signifies that everything behind the vehicle’s catalytic converter is being upgraded or replaced. Milltek's Sport Catback Exhaust Systems are designed to compensate for the sound reducing qualities from the particulate filter and significantly improve the sound aesthetic of the exhaust system.
By running pipes from the catalytic converter to the muffler and from the muffler to the exhaust tip, cat back exhaust systems improve exhaust gas flow, providing small performance boosts. However, your performance gains may be limited if your catalytic converter restricts gas flow, as a catback exhaust system is installed ‘downstream’ of the converter. Header-back systems are increasingly rare, namely because of modern emissions systems. Since removing your vehicle’s factory emissions components is highly illegal, the previous two options are more common. However, header-back systems are still available for some older, pre-emissions applications. In these cases, header-back systems offer more performance and volume than cat-back or axle-back systems