A cat-back system starts at the catalytic converter and replaces the pipes, mufflers, and tailpipes on your vehicle. It frees up some horsepower and can add torque to the motor as well. These systems are a common starting place for street-driven performance cars.
A header-back system starts at the headers or manifolds on the vehicle and replaces the entire exhaust system with new pipes, converters, mufflers, and tailpipes. Often these systems use larger diameter pipes and free-flowing mufflers to get a significant increase in power.
A full custom system offers the best increase in performance for your car. The system uses a larger diameter pipe and high-flow mufflers, and the pipes are bent to fit perfectly on your vehicle. Often the pipes are coated to reduce heat, and the bends are made on a machine that creates extremely smooth turns for the gases inside the exhaust system.