Removing the catalytic converter generally decreases fuel consumption, meaning it can improve fuel efficiency. This is because the catalytic converter restricts exhaust flow and creates backpressure, making the engine work harder and consume more fuel. Without the converter, exhaust gases exit more freely, which can result in the engine operating more efficiently and sometimes delivering up to 10% better fuel economy, especially in older vehicles[1][2][3].
However, the impact on fuel efficiency can vary. For most modern vehicles with a properly functioning catalytic converter, the improvement may be minimal, as these systems are designed to be efficient while meeting emissions standards[4]. In contrast, vehicles with older or clogged catalytic converters may see more noticeable improvements after removal.
It should be noted that removing the catalytic converter is illegal in many jurisdictions due to emissions regulations, and can lead to penalties. Furthermore, the environmental impact and potential warranty or inspection issues should also be considered before making such a modification[1][3].