If a "cat back" exhaust system includes all of the following EXCEPT?

A "cat back" exhaust system refers to the components of the exhaust system that run from the catalytic converter (often referred to as "cat") to the rear of the vehicle. Specifically, it typically includes parts like the intermediate pipe, muffler, and the exhaust tips.

The correct choice is the exhaust manifold because this component is situated at the front of the vehicle, connecting the engine's exhaust ports to the catalytic converter, and is not included in a "cat back" exhaust system. Instead, the exhaust manifold is part of the system that exists before the catalytic converter, which is not covered in this type of upgrade.

The other components, such as the new Y-pipe, intermediate pipe, and muffler, are integral parts that enhance the performance and sound of the exhaust system as they allow for better flow and less back pressure coming from the engine after the catalytic converter. Thus, the answer identifying the exhaust manifold as the exception is accurate within the context of a "cat back" exhaust system.