The 8 Best Catalytic Converters

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This wiki has been updated 25 times since it was first published in January of 2017. Most states require vehicles to undergo regular emissions testing, and a high pollution output or a check engine light are the most common ways that cars fail. But you don't have to spend hundreds to bring your exhaust system into compliance. As long as you don't live in California, New York, or Maine, there's a wide selection of universal-fit catalytic converters to help you do so. When users buy our independently chosen editorial choices, we may earn commissions to help fund the Wiki.

1. MagnaFlow 91005

2. Walker 93251

3. FlowMaster Universal

Editor's Notes

February 19, 2021:

As long as you don't live in one of the three states that currently have increased emissions requirements as compared to the federal level, the most important part of choosing a catalytic converter is whether it actually fits on your exhaust system, but there are some idiosyncrasies that make some models more effective than others. The MagnaFlow Heavy Metal and MagnaFlow CARB Compliant, for example, promise to remove more pollutants than most others, and although they're not compatible with vehicles that demand a catalytic O2 sensor, with modifications, they can be. Alternatively, the

AutoSaver88 410250 does have a sensor port, and claims to allow above-average airflow, ideal for cars with turbochargers or old and restrictive exhaust manifolds and piping. The AutoSaver88 High Flow offers even better volume, and its compact length and relatively sleek appearance make it suitable even for show cars.

Outside of specialized applications, the MagnaFlow 91005, Walker 93251, and FlowMaster Universal are all good choices for everyday cars in most states. In particular, the Walker has the compact size, sensor port, and heat shield needed to safely and effectively fit in most underbodies and provide environmental protection.

May 16, 2019:

First of all, we can't recommend any universal models in particular to most residents of California, New York, or Maine. All three of these states adhere to the relatively stringent CARB regulations (developed in CA) which surpass those set by the EPA. The only exception is the CARB-compliant universal pre-OBDII unit from Walker. It should work with most vehicles from before 1995. Walker also makes a fantastic 47-state option, but again, it's not legal in those three more demanding states.

With that in mind, there's nothing stopping vehicle owners in other states from using a California-certified unit like MagnaFlow's CARB-compliant converter. It costs a lot, but it's likely to last longer and reduce emissions more than the average universal model. Their 91005 is one of the most popular aftermarket choices, and their Heavy Metal version claims to do an even better job extracting harmful chemicals from exhaust. If you're looking for performance, look no further than FlowMaster, as they're very well-known among street modders and track-car builders for all of their high-flow exhaust parts. Finally, AutoSaver88 is a brand that few people may have heard of, but their product is pretty expansive, and most users seem quite satisfied with them. Most of their offerings are available with or without oxygen sensor ports.

Before you finalize your purchase, make absolutely certain that your choice is compatible with your vehicle. Also be aware that a universal-fit model will almost always require some cutting and welding, and sometimes some pipe bending. These may be tasks you're comfortable with, but it's likely that most people will want to pay a professional to install one of these. Don't worry, though; including the cost of labor, you'll still have saved money by purchasing an aftermarket catalytic converter in the first place.

Special Honors

MagnaFlow Exhaust Residents of New York, California, and Maine will need to purchase a unit that specifically matches their vehicle. Unfortunately, these tend to be very expensive, but they are better for the environment and tend to last considerably longer than universal or generic models. MagnaFlow is an excellent manufacturer of all exhaust products, catalytic converters included. Those in need of a CARB-compliant unit should head over to their website and enter their vehicle's information in order to find the right part.

4. AutoSaver88 High Flow

5. Walker CalCat

6. MagnaFlow CARB Compliant

7. MagnaFlow Heavy Metal

8. AutoSaver88 410250

A Catalyst For A Friendlier Environment

In another, this same invention is a rather dirty piece of hardware due to the harmful chemicals present in its exhaust when it's operating.

Most of us can relate to the experience of being stuck in bumper-to-bumper traffic during rush hour and seeing all that gross haze and air pollution emanating from the exhaust pipes found in a sea of automobiles. In one sense, the internal combustion engine is a marvel invention that has helped people get from one place to another with ease and efficiency. In another, this same invention is a rather dirty piece of hardware due to the harmful chemicals present in its exhaust when it's operating. Fortunately, many cars today are fitted with a device specifically-dedicated to reducing those harmful emissions by converting the poisonous chemicals into more environmentally-friendly gases that won't make you choke on the highway. This device is the catalytic converter.

While many pollutant gases consist of potentially problematic molecules, these molecules are made up of simpler and relatively harmless atoms. It is the job of a catalytic converter to help break these molecules down into smaller components and rearrange the atoms into less harmful substances once they leave a car's engine. Bolted to the underside of a car and located between the engine and tailpipe, a catalytic converter is a large, stainless steel box acting as an emission control device that's responsible for converting toxic pollutants, like carbon monoxide and nitrogen oxide, into less harmful gases before they're released into the atmosphere. The catalytic converter has several components that include a ribbed stainless steel body, ensuring durability and minimal distortion or expansion; substrates (also known as catalysts), acting as the backbone of the unit by driving the conversion process; a cushioning mat, responsible for holding the substrates in proper alignment and creating a seal between the substrates and body; body and pipe heat shields, designed to deflect excess heat away from a vehicle's undercarriage; and oxygen sensors, which monitor the converter's oxygen storage efficiency. The converter also has both an input and output pipe. The input pipe is connected directly to the engine and takes in the heated, polluted gases coming from the engine's cylinders. The output pipe is connected to a vehicle's exhaust pipe where the converted gas and water ultimately exit. But it's primarily the use of catalysts that allow the converter to do its magic.

Built to increase the speed of pollution removal from inside the converter and made from platinum or a similar metal like palladium or rhodium, the catalysts coat an internal, honeycomb-like ceramic core through which pollutant gases flow when they leave the engine. This honeycomb structure maximizes the degree of physical contact between gases and catalysts, allowing the gases to be converted as quickly as possible. A catalytic converter usually has two catalysts. One of them is responsible for breaking up nitrogen oxides into harmless nitrogen and oxygen gases through a chemical process known as reduction (i.e. removal of oxygen). The other catalyst works through an opposite chemical process called oxidation, which converts carbon monoxide into carbon dioxide through the addition of oxygen. A second oxidation reaction converts unused hydrocarbons from a vehicle's exhaust into carbon dioxide and water.

Catalytic converters are available in both two and three-way designs. Typically used in most diesel engines, two-way converters only perform the tasks of the two oxidation processes described above, while three-way converters have the additional advantage of performing both oxidation and reduction, resulting in superior emission control for most gasoline-powered engines.

Ensuring Safety And Compliance

Regardless of the type of vehicle you may be driving, there are several practical considerations to keep in mind when selecting the appropriate catalytic converter.

The first thing you'll want to do is narrow your search to those converters that actually fit your vehicle's make and model. You can often shop for a converter on a website that gives you access to this type of information before making a hasty decision.

The first thing you'll want to do is narrow your search to those converters that actually fit your vehicle's make and model.

Next, you'll need to identify the emissions level for your vehicle. Most emissions-compliant vehicles are equipped with a Vehicle Emissions Control Information label in their engine compartments that shows a factory OBDII emissions certification.

Depending on the certification, you must identify the proper converter grade you'll need. Three of the most common converter grades include standard, heavy metal, and OEM. For pre-OBD II vehicles (made in 1995 and before) and vehicles registered outside of the states of California, the standard grade is recommended. OEM grade is recommended for cars meeting the emissions standards set forth by the California Air Resources Board.

Once you've identified the proper converter grade, the final decision to make is whether you prefer a direct-fit or universal-fit unit. Direct-fit converters are designed for installation without any additional modifications, whereas universal-fit converters may require additional cutting, welding, and fabrication before installing them.

A Brief History Of Catalytic Converters

Up until the 1940s and early 1950s, a steady decline in air quality within major cities throughout the world sparked the need for some type of solution to the growing pollution problem. It was French chemical engineer Eugene Houdry who was credited with the development of the first catalytic converter in 1950, later having filed a patent for the device by 1954. Previously, Houdry had also invented catalytic cracking, the industrial process by which the many large and complex organic chemicals in petroleum could be separated into dozens of useful products, including gasoline. However, catalytic converters were essentially poisoned by the lead additives used in gasoline to improve a car's performance.

By 1973, the United States Environmental Protection Agency released a report detailing the health dangers of lead, resulting in the gradual removal of the harmful metal from gasoline. It was after this time that practical catalytic converters were engineered, including three-way converters.

Modern catalytic converters are designed to meet current emission safety standards with a primary goal of preventing excessive air pollution that would otherwise contribute to smog and decreased air quality, particularly in major metropolitan areas.

Christopher Thomas
Last updated by Christopher Thomas

Building PCs, remodeling, and cooking since he was young, quasi-renowned trumpeter Christopher Thomas traveled the USA performing at and organizing shows from an early age. His work experiences led him to open a catering company, eventually becoming a sous chef in several fine LA restaurants. He enjoys all sorts of barely necessary gadgets, specialty computing, cutting-edge video games, and modern social policy. He has given talks on debunking pseudoscience, the Dunning-Kruger effect, culinary technique, and traveling. After two decades of product and market research, Chris has a keen sense of what people want to know and how to explain it clearly. He delights in parsing complex subjects for anyone who will listen -- because teaching is the best way to ensure that you understand things yourself.

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