Are High Flow Cats Illegal? Legality and Performance Insights

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Are High Flow Cats Illegal

The question of whether high flow catalytic converters, commonly known as high flow cats, are legal is a topic of interest for many car enthusiasts and drivers who consider upgrading their vehicle’s exhaust system. This article provides an overview of the legality and performance aspects of high flow cats.

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Legality of High Flow Cats

The legality of high flow cats varies depending on the region. In the United States, replacing the factory catalytic converter with a high flow cat that meets federal emissions standards is generally legal. These high flow cats are designed to conform to the regulations set by the Environmental Protection Agency (EPA) and must bear an EPA-approved label. However, not all high flow cats are legal in every state. For instance, in California, a catalytic converter will only be legal if it comes with a CARB (California Air Resources Board) sticker, which is not commonly found on all cats.

Performance Aspects

High flow cats are designed to improve the exhaust flow from the engine by creating larger openings and using less restrictive material. This can lead to increases in power and torque, as well as improved fuel economy. However, they don’t necessarily boost performance significantly unless other engine parts are upgraded as well. It’s important to note that while high flow cats can increase emission flow, they might not pass emissions tests in some regions due to increased emissions.

Installation and Use Considerations

When considering installing a high flow cat, it’s crucial to understand both the legal implications and the potential effects on vehicle performance. It’s recommended to check local emissions regulations and ensure that the high flow cat is compliant with these standards. Additionally, understanding the specific needs of your vehicle and the expected performance outcomes is essential in making an informed decision.


High flow cats offer a potential improvement in vehicle performance, but their legality varies by region. It’s important for vehicle owners to be aware of the specific laws and regulations in their area and to choose a product that is compliant with these standards. By doing so, drivers can enjoy the benefits of an upgraded exhaust system while staying within legal boundaries.

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