Why does the engine noise increase after removing the three-way catalytic converter?

[LaLeo]

Removing the three-way catalytic converter results in increased engine noise because the converter, typically made of honeycomb ceramics or metal mesh, serves a certain level of noise reduction function. Function of the three-way catalytic converter: With increasingly stringent environmental protection requirements, more and more vehicles are equipped with exhaust catalytic converters and oxygen sensors. These devices convert harmful gases such as CO, HC, and NOx in vehicle exhaust into harmless carbon dioxide, water, and nitrogen through oxidation and reduction reactions. Since this catalytic converter can simultaneously transform various major harmful substances in the exhaust into harmless substances, it is called a three-way converter. Hazards of a damaged three-way catalytic converter: A damaged three-way catalytic converter does not affect the normal operation of the vehicle, but it can lead to difficulties in combustion, reduced driving power, engine backfiring, increased fuel consumption, incomplete combustion, carbon deposits in cylinders and spark plugs, and other phenomena. Over time, these issues can negatively impact the vehicle.

[OIsabelle]

I've been driving for over a decade and have encountered similar issues. Removing the catalytic converter does indeed make the engine sound louder, because the honeycomb ceramic structure inside the catalytic converter originally absorbed some exhaust sound waves, acting like a muffler layer for the exhaust pipe. Once removed, the exhaust flows unimpeded, allowing the sound to blast out directly. Moreover, removing the catalytic converter alters the exhaust backpressure, causing exhaust pulses to become chaotic at low RPMs. When I modified my car, I noticed particularly obvious noise below 2000 RPM, accompanied by metallic rattling sounds. What's worse, the exhaust fumes become extremely pungent, making it impossible to pass emissions testing. I strongly recommend reinstalling the proper OEM part as soon as possible.