2003-2013 Chevrolet Express 1500/2500/3500 Driver Side Exhaust Manifold Kit 674-522Product Overview: 1. Exhaust headers are a key upgrade for boosting engine performance by improving airflow. Unlike restrictive factory exhaust manifolds, performance headers give each cylinder its own dedicated exhaust path, reducing back pressure and improving exhaust flow. 2. By minimizing exhaust interference between cylinders, headers help increase horsepower and torque. When paired with a high performance cold air intake and a cat back exhaust