A high flow catalytic converter is usually the next step in increasing exhaust system performance after installing an aftermarket system, particularly a “cat-back” system. The term cat-back is where the catalytic converter (or cat, for short) is the next link in the chain as the exhaust system is traced back towards the motor. The catalytic converter can also be one of the main “choke points” or obstructions in the exhaust system, so replacing it can yield a definite increase in horsepower and overall performance.
To explain why a high-flow cat is more efficient, first it’s important to understand what the catalytic converter does and how.
The catalytic converter is part of the vehicle’s emissions control systems. Waste gasses from the motor contain harmful smog chemicals such as hydrocarbons, carbon monoxide and nitrogen oxides. It is the catalytic converter’s job to reduce these harmful emissions as much as possible in order to protect the air we breathe.
The way that the catalytic converter functions is simple. It forces the exhaust gasses to come in contact with a chemical catalyst, in this case the metals platinum or palladium. The catalyst causes the gasses to quickly degrade into less harmful substances, like carbon dioxide and water.
To ensure that the exhaust does come into contact with the catalyst, the catalytic converter contains a ceramic honeycomb coated with the catalyst metal which gases must flow through in order to continue along the exhaust path.
A high flow converter doesn’t function much differently than a stock unit. The point is that it must accomplish the same task as the stock unit but in a faster way. Performance modifications to the exhaust system always focus on increasing flow capability to allow the engine to breathe more easily so that it can make more power. The more quickly the catalytic converter can do its job, the higher its flow capability is.
High flow units typically use honeycomb designs. The flow rate can be increased either by increasing the overall cross section of the honeycomb (which allows the converter to contain more passages where the chemical reaction can take place) or widening the passages (which allows exhaust gasses to flow more freely). Designs with larger cross sections have to be engineered to fit within the alloted space on specific vehicles and designs with larger passages have to contain more catalyst metal in order to quicken the catalytic reaction. Either way, it’s important that the high flow cat not sacrifice effectiveness for greater efficiency or the environmental efficacy will be moot.
For this reason, you should always make sure that any catalytic converter you buy is from a reputable source and that it complies with the emissions laws in your state. Consult with an emissions repair shop in your area to make sure that you select a setup that is both legal and effective. Remember, it’s fun to go fast but protecting the environment is paramount responsibility.