Do you know what a catalytic converter is? There are so many catalytic converters on the market that it is dazzling, and which one to choose for installation? One or multiple? Direct-fit, universal, or a combination of both, or manifold? The following contents will detail the differences between the various catalytic converters.

What is a Catalytic Converter?

The catalytic converter, also called cat for short, is sometimes referred to simply as caton. It is placed on the engine and converts harmful nitrogen oxides and carbon monoxide into ubiquitous CO₂, N₂, and H₂O via heterogeneous catalysis. For more relevant information, please read our another blog on knowing what is a three way catalytic (TWC) converter and how it works.

One VS Multiple

In order to better curb exhaust emissions, the EPA has issued a new regulation for 'Cold Start' at warm ambient temperatures. As a result, it is crucial that the engine of a catalytic converter is ignited apace. For compliance with this regulation of Start Emissions, many vehicles pack the catalytic converter next to the exhaust ports, which can quickly reach the minimum temperature of ignition, and then start working. However, packing the full-size cat next to the engine exhaust ports is particularly difficult. To address this, a smaller cat is tightly coupled as close to the exhaust ports as possible, and another larger one (the main cat) is located underbody for easier placement.

In the past, many older models of vehicles had only one mounting location for the catalytic converter. Many automakers continue to try to increase compression, which in turn produces nitrogen oxides. Thus, to comply with progressively stricter emissions regulations, one of the approaches they took was to add more catalytic converters and make them interconnected. In simple words, more catalytic converters are used to accomplish fewer emissions of nitrogen oxides.

In fact, whether you choose one converter or multiple converters, please match the location provided by your vehicle.

Different Methods of Installation

There are several methods of cat installation, including Direct-fit, Weld-on, the combination of both connections, and manifold. Please ensure that your vehicle meets Federal EPA standards, or California requirements without being registered in California, New York, Colorado, and Maine. At the same time, check if the oxygen sensors are intact. If not, replace them as well.

Direct-fit Catalytic Converter

Direct-fit catalytic converters are equipped with well-designed flanges on both ends to facilitate installation: Only insert matched gaskets into the correct position, and screw all bolts tightly. The connection process only requires ordinary hand tools instead of cutting and/or welding.

Therefore, Direct-fit catalytic converters can be installed easily by yourself, as long as you confirm the matching model first.

Weld-on Catalytic Converter

In general, Weld-on catalytic converters are universal fitment, they are compatible with a number of vehicle models. As you make sure that the inlet and outlet pipes of the catalytic converter and exhaust system are of the same diameter, you can proceed with the Weld-on installation.

Before welding, please connect the inlet and outlet of the catalytic converter to the exhaust pipe and extension pipe of the engine exhaust system respectively. Even if the diameter match of tubes has been confirmed, the connection may be still difficult due to rusting of other parts in your vehicle. Then at this point, it is time to use a pipe expansion tool. Simply use the pipe expansion tool to expand or shrink one of the pipes that need to be welded until they can smoothly slide into each other, and then seal them with welding. This installation procedure is highly recommended for professionals to operate, so that the cat is able to play a maximum role.

Direct-fit & Weld-on Catalytic Converter

As a matter of fact, there are fewer models that use a combination of the two types of mounting, but they still exist. For the best alignment on specific vehicles, one end of the catalytic converter adopts a Direct-fit connection, and the other end is welded.

Manifold Catalytic Converter

Manifold catalytic converters are similar to Direct-fit catalytic converters in that they are also flanged in design and bolted Directly to the vehicle. Usually, catalytic converters are not required to replace the exhaust manifold. The exhaust manifold concentrates the exhaust gases from multiple pistons into the main exhaust pipe, which then conveys them to a catalytic converter placed further down this pipe for purification. But the installation of a manifold catalytic converter maybe require the removal and replacement of the entire manifold, and a professional installer who knows advanced mechanical knowledge is needed to do so.

Therefore, the manifold converter is usually more expensive than a Direct-fit or universal catalytic converter. In this case, why is a manifold catalytic converter needed? On the one hand, both manifold and catalytic converter are installed as a whole rather than separate welded parts, which can save space in the engine installation to a large extent. On the other hand, the location of the exhaust manifold allows for faster heating, helping to improve conversion efficiency during 'Cold Start' as soon as possible.

Summary

Which type of catalytic converter should be used?

Direct-fit catalytic converters are designed for specific vehicles. They have been machined during the manufacture so that they don’t require any further modifications and are installed Directly using flanges and bolts. Thus, you can easily replace them at home, even though the cost is higher compared to universal catalytic converters.

Universal catalytic converters, however, can be used on a range of makes and models as long as the diameter matches your vehicle, and the cost will be relatively affordable. However, the diameter of the pipe inlet or outlet may need to be fine-tuned before use, which is a bit difficult for novices or junior DIY mechanics to install and require the help of a more professional for replacement. That is, maybe you need to spend some money on labor costs.

The above two types dominate the three way catalytic converters. Even the manifold catalytic converter actually belongs to a Direct-fit type, with some minor differences. At Daysyore Auto Parts, we provide more information about catalytic converters for your convenience.