How an Exhaust Manifold Works

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Here's a look at whats inside an exhaust manifold and how it works on your car.

The exhaust manifold, or exhaust header, is responsible for removing exhaust gases from the engine cylinders and directing it toward the catalytic converter.

The exhaust stream is collected from each cylinder and flows into the collector, where the pipes join into one main pipe. It then flows past an air to fuel ratio sensor before connecting to the catalytic converter and then tail pipe.

The manifold has a double walled design after the collector to the catalytic converter to help with heat insulation. Often, a flexible exhaust pipe is located after the header to isolate engine vibration from the rest of the exhaust system.

The shape, diameter and length of each tube on the manifold is designed such that the scavenging effect, sound and performance of the engine is optimized.

The scavenging effect occurs when at the tail end of an exhaust pressure pulse where a low pressure zone is created. The low pressure zone helps to suck out remaining exhaust gases in the cylinder, and also bring in fresh air from the intake side at the moment in the combustion cycle when the intake and exhaust valves are open.

Aftermarket exhaust headers will make the pipes larger for a freer flowing exhaust. However, that decreases the velocity of the pressure pulses in the manifold, thus decreasing the scavenging effect. Therefore an ideal balance must be made when designing a header.

The exhaust manifold in this video was removed from a 2001 Toyota Corolla with the 1ZZ-FE VVT-i engine.