Catalytic Converter Buying Guide


Catalytic converters are vital to both your vehicle and our planet’s precious atmosphere. But, no matter how essential these components may be — and trust us, they are — we understand that you may have some questions about them. What they are, where they go, what they’re designed to do… How can you tell which emissions regulations they meet? Should you go for a direct-fit converter or a universal one? These are all valid questions, and this guide aims to provide you with not only the history and purpose of these parts, but expert advice and pro tips on picking and installing the right cat converters for your vehicle.

WHAT DOES IT DO?First invented in the mid-1950s by mechanical engineer Eugène Houdry in response to unsettling smog studies done in Los Angeles, the catalytic converter reduces the toxicity of exhaust emissions. They work on both gas and diesel applications, and while most are legal in all 50 states, there may be some that won’t fly in California or other states adopting California emission standards.

Harmful substances like carbon monoxide, nitrogen oxides and hydrocarbons are “converted” — hence the name — into harmless ones. Carbon monoxide, a poisonous gas, is render into carbon dioxide; nitrogen oxides, which cause acid rain and smog, turns into nitrogen and oxygen; and hydrocarbon, responsible for respiratory problems, is changed into carbon dioxide and water.

You’ll be able to feel the day your cat converters go bad, too — an old or clogged component robs your vehicle of power and responsiveness. Moreover, if one of the cats goes bad, it’s recommended you replace them all at once, as you would your worn-out tires or brakes.

Structurally, a catalytic converter is basically a stainless steel box that attaches to the muffler. They contain ceramic beads or are honeycomb-coated with catalysts — usually alumina, ceria and other compounds combined with palladium, platinum, rhodium and even gold. They’re also packed with sensors, which regulate the fuel and air passing through your engine.

Most modern vehicles actually have more than one cat in their arsenal, which is why it’s important that you note the location or position of yours. There are driver’s side and passenger’s side cats, which is purely subjective to which way you’re standing or facing. Also, while they’re primarily used on cars, cat converters may also be applied to motorcycles, electrical generators, forklifts, mining machinery, cargo trucks, buses and trains.

FEDERAL OR CARB? Before you go all-in for the first converters you set eyes on, it’s important that you first identify what kind of emission system with which your vehicle came — one that adheres to either Federal or CARB regulations. To do this, just pop your hood and locate the emissions equipment sticker, which will either be directly on the underside of your hood or near the firewall area behind the engine. Federal standards are in-line with those set down by the Environmental Protection Agency (EPA), but California Air Resources Board (CARB) regulations are much stricter. They also require more precious metals and more rigorous testing, which is why they also cost more than EPA cats.

  • If your vehicle was originally sold in California, its emissions equipment will be CARB-compliant.
  • If it was originally sold in one of the other 49, it may or may not be CARB-approved. It depends on whether the state follows California emission standards. Check that state’s DMV site for more info.
  • If it’s CARB-compliant, your converter will be labeled as such with a certification stamp or label on the shell, which includes the CARB Executive Order approval number, part number, date of manufacturer and installation directions.

What is CARB, you ask, and why is this estimable body less relaxed than the EPA? A regulatory agency responsible for maintaining healthy air-quality, CARB has defended American citizens from toxic air conditions since its foundation in 1967 by then-California Gov. Ronald Reagan. It was formed as a response to Los Angeles’ severe smog problems and subsequently set high watermarks for controlling vehicle emissions-based pollution. And, although it’s governed in California, other states can follow CARB standards, as said above. Currently, the states which follow CARB regulations (as seen on the map above) are Arizona, California, Connecticut, Maine, Maryland, Massachusetts, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont, Washington, and even the District of Columbia.

DIRECT-FIT OR UNIVERSAL?Direct-fit converters bolt directly onto your vehicle. A favorite of seasoned DIYers who have already invested in the appropriate tools, they’re best-suited for vehicles with an OEM-style exhaust system, or one that’s still factory-fitted.

Universal converters are generally cheaper than their direct-fit counterparts, and are suitable for wide-ranging application. WARNING: The installation process is anything but easy, requiring the use of various tools to cut the pipes down to the appropriate length. Components and vehicle-specific parts come separately. Overall, it’s a more labor-intensive process and could wind up a waste of your time, effort and money, as the return rate on these products tends to be high. So, while we do, in fact, carry universal converters, we recommend you go with the direct-fit. If you’re dead-set on a universal option, though, you should probably have it done professionally.

WHAT IS MY EFN? And why is it relevant? Does your vehicle even have one? If it was manufactured post-1995, then it does. Simply put, the EFN (short for “Engine Family Number”) is a number given to your specific engine, which you need to know in order to buy the correct cat converter. You’ll also need to know the basic year, make, model and engine type, as well as the transmission type or sub-model, but for some reason, most people are unaware of what their EFN is and where they can find it. It identifies both the engine and your vehicle’s emissions.

Your vehicle’s EFN is located under the hood on the Vehicle Emissions Control Information (VECI) label. Depending on your make and model, the VECI label may be located in a number of locations. Typically, the label will be on the underside of your hood or on the fender well. The EFN is displayed on this label.

Steps to finding the EFN:

  1. Pop the hood and prop it open
  2. Look for your emissions sticker
  3. Locate the EFN number
  4. Write down the EFN and reference it when buying your catalytic converter