Do Catalytic Converters Really Rob Your Car of Power?


Catalytic converters are emission control devices that were first developed in the 1950s by Eugene Houdry to reduce air pollution from vehicle exhaust. They were mandated for use in U.S. passenger vehicles starting in 1975 as part of the Clean Air Act Amendments to meet increasingly strict emissions standards.

Catalytic converters work by using a catalyst to facilitate chemical reactions that convert harmful exhaust pollutants like carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful emissions like carbon dioxide, water, and nitrogen. This helps reduce the emissions from internal combustion engines that contribute to air pollution and smog.

By installing a catalytic converter, vehicles can meet the tailpipe regulations for air quality set by regulatory agencies. They have become a crucial emissions control component for most gasoline-powered vehicles around the world.

How Catalytic Converters Work

Catalytic converters use a chemical process to reduce the amount of harmful emissions from a vehicle’s exhaust. Inside the converter is a honeycomb-like structure coated with precious metals like platinum, palladium and rhodium that serve as catalysts. As exhaust gases pass through, the catalysts facilitate chemical reactions that convert pollutants like hydrocarbons, carbon monoxide and nitrogen oxides into less harmful compounds like nitrogen, carbon dioxide and water vapor (Source 1).

Specifically, the catalysts oxidize carbon monoxide and hydrocarbons, turning them into carbon dioxide and water. They also reduce nitrogen oxides into nitrogen and oxygen. According to Harvard researchers, catalytic converters can eliminate up to 98% of pollutants from engine exhaust (Source 2). This chemical process enables catalytic converters to dramatically reduce the emissions coming from a vehicle’s tailpipe.

Effect on Engine Performance

Catalytic converters create backpressure that can reduce an engine’s power output. As exhaust gases pass through the converter, they encounter resistance from the honeycomb structure and catalyzing materials inside. This resistance restricts the flow of exhaust gases out of the engine, creating backpressure in the exhaust system.

Higher backpressure makes it more difficult for the engine to expel spent exhaust gases after every combustion cycle. The engine has to work harder to push the gases out against the added resistance of the converter. This extra work can result in less power sent to the wheels.1

Significant converter blockage due to failure or damage can greatly increase backpressure levels. This leads to more exhaust remaining in the combustion chamber after each cycle, negatively impacting engine performance. Symptoms may include loss of power, especially at high RPMs, as well as rough idle and acceleration issues.2

Design Improvements

Catalytic converters have undergone design changes over the years to improve performance and reduce backpressure. Early catalytic converters used a two-way design that focused on oxidizing hydrocarbons and carbon monoxide into carbon dioxide and water. These converters caused significant backpressure that reduced engine power.

Modern three-way catalytic converters integrate reduction and oxidation functions to also reduce nitrogen oxide emissions. Improved catalysts and substrate designs help reduce flow restriction while still filtering emissions effectively. Cell density, or the number of small channels in the substrate, has increased which improves flow rate. Thin, tightly spaced walls between the channels maximize surface area exposure to exhaust gases without impeding flow.

High-flow metallic or ceramic substrates are now commonly used which are more porous and cause less backpressure compared to earlier ceramic only designs ( Also, some performance converters are now being designed with larger substrates that increase flow. These improvements allow modern catalytic converters to filter emissions efficiently while minimizing power loss.

High Flow Converters

Aftermarket high flow catalytic converters are designed to optimize exhaust flow and minimize restrictions, rather than focusing solely on emissions reduction like OEM converters. According to Discount Converter, “High flow converters have less dense catalyst substrates with larger exhaust channels inside the core. This allows for free flowing exhaust gases to pass through with less back pressure and restriction.”

By reducing backpressure, high flow converters can help improve peak power and torque. As Euro Sport Tuning explains, “The less restricted the exhaust gases are, the more efficiently the engine can expel them, allowing it to function optimally.” However, high flow converters may allow more emissions to pass through than standard OEM converters.

Overall, high flow catalytic converters aim to strike a balance between lowering emissions and reducing restrictive exhaust backpressure for performance gains. But their legality varies by location, and they may not be emissions compliant in all areas.

Fuel Economy

Catalytic converters can have a negative impact on fuel economy due to the increased backpressure they create in the exhaust system. As exhaust gases pass through the catalytic converter, they encounter resistance which restricts flow. This backpressure forces the engine to work harder to expel exhaust gases, increasing fuel consumption.

Most sources estimate that catalytic converters reduce fuel economy by 2-3%. For example, a car that normally gets 25 mpg may only achieve 24-24.5 mpg after installing a catalytic converter ( While not a huge decrease, it can add up over time, especially for vehicles that drive long distances frequently.

Some drivers try to improve fuel economy by removing the catalytic converter. However, this is illegal in many jurisdictions due to increased emissions. Improperly removing or tampering with emissions equipment can also void a vehicle’s warranty.

Aftermarket Upgrades

For modified engines, especially those with forced induction or nitrous systems, the stock catalytic converter can create a bottleneck that restricts exhaust flow and hurts power. Aftermarket converters with higher flow are a popular upgrade to remove this restriction.

Options like the Magnaflow 10416 Manifold Catalytic Converter (1) offer minimal backpressure and increased flow for tuned engines. Companies like MagnaFlow engineer their performance cats specifically for modified vehicles to maintain emissions compliance while maximizing power.

Larger 3-inch or 3.5-inch inlet/outlet diameters greatly improve exhaust velocity compared to the stock 2.25-2.5 inch cats. Stainless steel or aluminized steel construction is also more durable than factory converters.

For the biggest power gains, high-flow catalytic converters with larger piping, free-flowing internals, and 200-400 cell per inch (CPSI) density substrates are recommended. Properly sized units avoid airflow restrictions while still filtering enough emissions for street legality.

Racing Use

Catalytic converters are often removed from racing vehicles to maximize performance, as they can create exhaust backpressure and reduce power output. High performance racing engines are tuned for maximum power, not emissions control. According to Ace Race Parts, racing series in Europe require catalytic converters for noise reduction, but racers can use high flow racing converters that reduce backpressure.

Many forms of motorsport racing allow the removal of catalytic converters to gain power, including drag racing, rally racing, and some circle track racing series. However, some sanctioning bodies like NASCAR require approved catalytic converters to control emissions and noise. Aftermarket high flow converters are available that meet racing regulations while minimizing power loss.

Legal Restrictions

Catalytic converters are required by federal law in the United States for all gasoline engines produced after 1975. The Clean Air Act mandated their use to help reduce air pollution from vehicle emissions. Removing a catalytic converter from a vehicle intended for street use is illegal under this federal law.

Additionally, many states have their own laws regarding catalytic converters. California, for example, requires CARB-approved catalytic converters on vehicles model year 2001 or newer. It is illegal in California to remove or replace a catalytic converter with a non-CARB approved one. Other states like Colorado also prohibit removing catalytic converters from vehicles more than five years old where the original converter warranty has expired.

Violating catalytic converter laws can result in substantial fines. Mechanics or individuals who remove converters could face penalties up to $25,000 per violation. Before modifying any vehicle’s emissions equipment, it’s important to check both federal and state laws.


In summary, catalytic converters do have some negative effects on engine performance, but the impacts have lessened over time as converter technology and engine design has improved. The small power loss from backpressure is offset by more complete combustion and exhaust scavenging provided by the converters. For most drivers, the minor performance effects are outweighed by the emissions reduction benefits. However, high performance enthusiasts and racers frequently replace converters with less restrictive aftermarket units to maximize power output. Overall, catalytic converters remain an essential emissions control technology for street-legal vehicles despite having a slight detrimental impact on peak engine performance. As long as emissions regulations remain in place, engineers will continue working to minimize the tradeoffs between power, efficiency, and emissions reduction.

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