Does a catalytic converter reduce power?

In most modern cars, a healthy catalytic converter has little to no noticeable impact on engine power; any loss is typically marginal (often within 0–2% at peak output) and outweighed by emissions benefits. Significant power loss usually appears only when a converter is clogged or in very high-output builds where exhaust flow far exceeds stock design. Here’s how and why the effect varies by vehicle and condition.

What a catalytic converter does—and why its impact on power is small today

A catalytic converter uses a ceramic or metallic honeycomb coated with precious metals (platinum, palladium, rhodium) to convert harmful exhaust gases into less toxic compounds. That honeycomb does add some restriction to the exhaust stream, creating a small pressure drop. However, modern “high-flow” three-way catalysts are engineered to minimize that restriction with optimized cell density, thin walls, and larger cross-sections, making their effect on performance negligible for stock vehicles. Engine calibrations are also designed with the converter in place, so drivability and power curves assume its presence.

How much power can it cost in the real world?

The impact depends on engine type, output level, converter condition, and calibration. On a stock naturally aspirated engine, differences are often within dyno measurement noise. Turbocharged setups can be more sensitive to post-turbine backpressure, but modern high-flow converters typically keep the penalty very small when the system is sized correctly.

Below are common scenarios and the typical effect enthusiasts and testers observe.

• Stock naturally aspirated engines: Usually 0–2% peak power difference versus a straight pipe, often imperceptible in normal driving.
• Stock turbocharged engines: Small high-rpm restriction can appear (roughly 1–3% before any recalibration). With an appropriately sized high-flow catalytic converter and a proper tune, the difference is often below 1–2% and may be hard to detect.
• High-output or heavily modified builds: As flow rises far above stock, the converter can become a bottleneck. A larger, motorsport-grade “high-flow” unit typically recovers most of the loss; catless systems may show modest additional gains (often a few percent), especially at high boost—at the expense of legality and emissions.
• Failing or clogged converters: Power can drop dramatically, with poor acceleration and high exhaust backpressure; this is a fault condition, not a normal characteristic of functioning catalysts.

In short, healthy modern catalysts are designed to be invisible to the driver on stock vehicles, while failures or extreme power levels are where notable differences emerge.

When a catalytic converter actually hurts performance

Meaningful power loss usually points to a converter that’s damaged, contaminated, or clogged. Causes include misfires, oil or coolant consumption, lead or silicon contamination, and thermal meltdown from unburned fuel. Early diagnosis prevents further engine and exhaust damage.

Watch for these common signs of a restricted or failing catalytic converter.

• Sluggish acceleration, especially at higher rpm or sustained loads, and a tendency to “fall flat” as revs climb.
• Excessive exhaust backpressure readings or a noticeable drop in manifold vacuum at higher rpm.
• Overheating or glowing red converter housing after hard driving; sulfur/rotten-egg smells from the exhaust.
• Check engine lights such as P0420/P0430 (catalyst efficiency below threshold). Note these codes don’t always mean a clog; they can indicate chemical inefficiency or sensor issues.
• Poor fuel economy or misfire history (which can quickly damage the substrate).

If these symptoms appear, confirm with backpressure tests, temperature comparisons, or a borescope inspection, and address root causes like misfires or oil consumption alongside any converter replacement.

High-flow and motorsport options

For builds aiming to increase power while staying clean, “high-flow” catalytic converters use lower cell densities and larger cores to reduce pressure drop. In many cases, a well-matched high-flow, emissions-compliant converter retains legality and delivers performance within a whisper of catless systems, especially once the ECU is calibrated for the hardware.

Below are practical ways to preserve performance without sacrificing compliance.

• Select an OEM-quality or certified performance converter sized for your power goals (e.g., CARB EO-certified in the U.S. where required).
• Match exhaust diameter and downpipe design to anticipated flow, particularly on turbo engines to minimize post-turbine backpressure.
• Get a proper ECU calibration after hardware changes so fueling, boost control, and timing account for the converter’s characteristics.
• Maintain the engine to prevent catalyst poisoning: fix misfires promptly, address oil/coolant consumption, and use the correct fuel and oils.
• Ensure oxygen sensors are healthy; bad sensors can trigger false catalyst codes or poor fueling that harms the converter.

Done correctly, these steps keep emissions systems intact while preserving, and often improving, drivability and consistent power delivery.

Legal and environmental considerations

Removing or tampering with catalytic converters is illegal for street use in many jurisdictions, including under the U.S. Clean Air Act, and can result in substantial fines and inspection failures. Beyond legality, converters are the primary barrier between engine-out emissions and the air we breathe; removing them dramatically increases pollutants like CO, NOx, and HC. For track-only vehicles, consult series rules—many modern race classes now permit or require high-flow catalysts to reduce environmental impact with minimal performance tradeoff.

FAQs

Does removing a catalytic converter improve fuel economy?

Usually not. Modern ECUs target stoichiometric air-fuel ratios in closed-loop operation and optimize efficiency with the converter in place. Cat removal can trigger check-engine lights and protective strategies that hurt economy and drivability.

Will a high-flow catalytic converter trigger a check-engine light?

It can if it’s not sufficiently efficient for the vehicle’s calibration. Using an approved, properly sized unit (and, if needed, an appropriate tune) minimizes P0420/P0430 codes. “Spacers” or sensor tricks are typically illegal for road use.

How long do catalytic converters last?

Many last 10–15 years or 100,000–150,000 miles or more. Lifespan depends on engine health, fuel quality, and driving patterns; persistent misfires or oil burning can shorten it dramatically.

Bottom line

A modern, healthy catalytic converter has a minimal effect on power in stock vehicles, often within the margin of testing error. Noticeable losses point to faults (like clogging) or extreme performance demands. For most drivers—and many enthusiasts—an appropriately sized, emissions-compliant high-flow converter delivers clean air with virtually no sacrifice in real-world performance.

Do catalytic converters reduce engine performance?

Backpressure: Catalytic converters, due to their design and placement within the exhaust system, can introduce some backpressure, which can affect engine performance and, consequently, fuel efficiency. Backpressure is the resistance to the flow of exhaust gases caused by the converter.

Does removing a catalytic converter increase power?

Yes, removing a catalytic converter can increase power because it reduces exhaust backpressure, allowing the engine to “breathe” more freely, though the actual power gain varies and may be negated by negative consequences like poor engine control, a lit “check engine” light, and adverse effects on air quality. The engine’s computer may also attempt to compensate for the change, leading to even worse performance or fuel issues. 
Why Power May Increase

• Reduced Backpressure: Opens in new tabA catalytic converter restricts exhaust flow, and removing it allows exhaust gases to exit the engine faster, increasing horsepower. 
• Engine Efficiency: Opens in new tabAn engine functions as an air pump, and less resistance from the exhaust system means the engine can operate more efficiently and effectively. 

Why Power Might Not Increase (or could decrease)

• Engine Control Issues: Modern vehicles have engine control units (ECUs) that monitor and manage engine performance, including emissions components like the catalytic converter. 
• False Sensor Data: If a catalytic converter is removed, the oxygen sensors will send incorrect data to the ECU. 
• Poor Performance: The ECU’s response to these false readings can lead to a fuel mixture that is too rich or too lean, causing the engine to run poorly and potentially lose power. 
• Check Engine Light: A missing or compromised catalytic converter will trigger the “check engine” warning light. 

Other Consequences

• Increased Pollution: Catalytic converters are essential for reducing harmful emissions, so removing them will significantly increase your vehicle’s pollution. 
• Legal Issues: Tampering with or removing a catalytic converter is illegal in many places. 
• Engine Damage: An improperly controlled engine can overheat, knock, or suffer premature wear and tear. 

Can a catalytic converter cause loss of power?

Loss of Power: A clogged catalytic converter can restrict the engine’s ability to expel exhaust gases, resulting in a decrease in engine power and performance. Stalling: If the exhaust flow is severely restricted, the engine may stall or shut off, especially at low speeds or when idling.

Will removing a catalytic converter hurt the engine?

Removing a catalytic converter can hurt your car by triggering a check engine light, causing performance issues, and potentially causing damage to other engine or exhaust components over time due to increased exhaust temperatures and incorrect sensor data. Modern vehicles use oxygen sensors to monitor the catalytic converter, and without it, the engine’s computer can malfunction, leading to a poor air-fuel mixture, reduced fuel efficiency, and a rougher-running engine.
 
Effects on Engine Performance

• Engine Light and Error Codes: The car’s computer (ECM) is designed to work with the catalytic converter and will trigger a check engine light when it’s missing. 
• Incorrect Air/Fuel Mixture: The oxygen sensors read the exhaust gases, and without a functioning converter, the rear oxygen sensor sends faulty data to the ECM. The ECM may then dump excessive fuel into the engine, causing it to run rich, which negatively impacts engine performance. 
• Rough Running: The engine may run rougher, stutter, or even stall, especially at low speeds or during acceleration. 
• Reduced Power: You may experience a drop in engine power and poorer fuel economy. 

Potential for Damage

• Increased Exhaust Temperatures: The catalytic converter helps dissipate heat. Removing it can increase exhaust temperatures, potentially causing damage to other components in the exhaust system. 
• Damage from Improper Operation: Continuously running with a faulty air-fuel mixture can lead to damage to other components over time. 

Why It’s Not Recommended 

• Illegal: Removing or bypassing a catalytic converter is illegal and can lead to fines and tickets due to Environmental Protection Agency (EPA) regulations.
• Environmental Harm: The primary purpose of a catalytic converter is to reduce harmful pollutants from exhaust gases.
• Increased Noise: Catalytic converters also act as a partial muffler, so removing one will result in a significantly louder exhaust noise.