The automobile engine is like an air pump; the more air that flows through it, the more horsepower it produces. A free-flowing air intake and exhaust system will produce more horsepower because of the efficient flow of air into and out of the engine. Fuel requires air to burn and thus to produce mechanical energy. The more air that is available for combustion will improve the efficiency of the motor, increasing gas mileage and power. The exhaust system removes the gaseous by-products of internal combustion.

The exhaust manifold is a pipe that conducts the gases from the combustion chambers to the exhaust pipe. The exhaust manifold contains a port for each exhaust port in the cylinder head, and the manifold fits against the exhaust port area on the cylinder head. Gaskets are used to prevent leakage of gases between the manifold and cylinder heads. The exhaust passages from each port in the manifold join into a common single passage before reaching the manifold flange. The exhaust pipe is connected to the exhaust manifold flange.

The exhaust pipe is connected from the exhaust manifold to the catalytic converter. Unleaded gasoline must always be used in engines with catalytic converters. If leaded gasoline were to be used, lead in the gasoline coats the catalyst and renders it ineffective. Under this condition, tail pipe emissions become elevated. An engine that is improperly tuned would also cause severe overheating of the catalytic converter.

After the catalytic converter, gasses pass into the muffler. The reverse-flow muffler is the most common design. This design changes the direction of exhaust flow inside the muffler. Exhaust gases are directed to a third chamber, forced forward into the first chamber, from where they travel the length of the muffler and are then exhausted into the tailpipe.

Some mufflers are a straight through design in which the exhaust gases passes through a single perforated pipe into a outside chamber packed with metal, packed glass, fiberglass, or other sound absorbing material. This type of muffler is thus freer flowing and designed for the purpose of reducing back-pressure and produces slightly more noise than a reverse flow muffler.

The tail pipe basically carries the flow of exhaust from the muffler to the rear of the vehicle. Tail pipes have bends to fit around the chassis and other components. The tail pipe usually extends under the rear bumper, with the end of this pipe is cut at an angle to deflect the exhaust downward.

There are several different exhaust systems that can increase engine horsepower and performance. These called performance systems, using modified manifolds, or muffler/exhaust systems to reduce back pressure and increase engine airflow.