Starting from the engine you have the headers. These four pipes collect from each cylinder the exhaust fumes and channel them down into one pipe. The first thing after the header is the Catalytic converter. The catalytic converter "convert's" harmful pollutants into less harmful emissions, now these are regulated by an oxygen (o2) sensor that is connected to your cars ECU. Catback exhaust's usually start after the "cat" and head back, hence the name. Next in the middle of the piping is the resonator. The resonator is like a muffler that acts too minimize cabin drone. After the resonator you have the muffler then the tip. A muffler is designed solely to reduce "sound" in an exhaust system. It "mostly" doesn't stop any pollution, carbon dioxide, etc. (like the catalytic converter.) Removing the muffler will just make your car louder, case in point. It doesn't affect any "exhaust valves", doesn't tamper with the ECU, and will not cause rod knock in your motor.
