The exhaust system and components on the 2004.5–2007 5.9L Cummins manage the flow of exhaust gases from the engine to the tailpipe, reducing backpressure and improving performance. Key parts include the exhaust manifold, turbocharger, downpipe, catalytic converter (if equipped), muffler, and tailpipe. Upgrading to high-flow systems or aftermarket components can boost horsepower, enhance turbo spool-up, and deliver a more aggressive sound. Quality materials like stainless steel improve durability, especially in high-heat or harsh driving conditions.