What is a Catalytic converter and how does it work?
A catalytic converter is a device used to reduce harmful emissions released from a car’s exhaust. It can be found between the extractors and muffler. Emissions from car’s exhaust consist of noxious gases such as carbon monoxide, hydrocarbons and nitrogen oxide. They are responsible for smog, myriad respiratory problems and damage to plant life.
Emissions pass through a Ceramic honeycomb catalyst structure (normally consisting of a metallic catalysts, platinum, rhodium or palladium) that causes a chemical reaction with the noxious gases, converting them into less harmful gases such as carbon dioxide, nitrogen and water vapors.
OEM Cat converters Vs Hi-Flow Cat Converters
OEM type Catalytic converters do a great job at controlling and reducing emissions; however they are restrictive by design (bottle neck inlet/ outlet and a very dense honey comb cell structure). Stock factory cat of Holden VY commodore SS (on one side) has been tested to show a flow rate of 250cfm. Xforce Metallic and Ceramic High flow cats has shown to flow as much as 550cfm for a 2.5″ ceramic cat (400cell), and 750cfm for a 3” metallic cat (200cell as tested). Replacing the factory item for an Xforce High flow racing cat can show a significant increase in Horsepower.
What type of cats you should use:
The two most common used aftermarket cats are: Ceramic substrate and metallic substrate catalytic converters.
- Ceramic cats in general have lower flow rate than metallic cats.
- Ceramic cats are more economical while metallic cats cost more.
- Ceramic cats are ideal for Modest Modifications
- Metallic cats are more durable than the ceramic cats, more shock resistance than the ceramic substrate.
- Metallic cats can support higher Exhaust gas flow speed and higher exhaust temperature,
- Metallic cats are ideal for highly modified cars
MIL/ CEL issues
Installing hi-flow racing cats could trigger the CEL(Check Engine Light) or MIL (Malfunction Indicator Light) on the dash usually occurring in later model cars. In Australia, late model cars (2005 onward) are required to have a second O2 sensor located immediately after the factory cat. This allows the ECU to detect any changes in emission condition, malfunction or inefficiency of the cat, unfortunately it also interprets the “hi-flow” characteristic of performance cats as inefficient emission control. If the diagnostic code is scanned by DTC scanner, the code will likely to be something like “P0420: catalyst efficiency below threshold”.
“CEL eliminators” are available on the market to help solve this common issue; however it should be noted that they can also produce mix results. A “CEL eliminator” is basically an O2 sensor bung adaptor, which is fitted between a factory O2 sensor bung (seating) and the O2 Sensor. Some have small sections of cat converter fitted inside the tube, some don’t. We found that none of the latter (the one without cats) works so far, while the former one (with cats) work on some cars, but not all of them. They act as “filters” for the exhaust gas before they reach the O2 sensor. After much testing we concluded that the results will depend on how good the small cats inside the adaptor are, and also the sensitivity of the sensor.
The best solution we feel to remedy this problem is an ECU tune including a “ECU Flash Tune”, which are available from many performance Workshops.
Hi-flow aftermarket cats have shown to produce significant power gain, especially for high-end performance applications. However this is at the cost of less emission control over the factory stock units, so it only suitable and is advisable for race and off road applications.
After installation of a hi-flow cat, there will be much less back pressure resulting in increased gas flow, and sound/noise level. The higher flowing the cat is, the higher the sound level will be. Typically the difference in sound level before and after a high flow cat can be from 2~4 dB for a hi-flow 100 or 200 cell metallic cat.
When planning a new exhaust system, the type of cats should be considered as an important factor that can affect the exhaust sound characteristics. As an example, if your aftermarket cat-back system is too quiet and you are plan to upgrade the system for more noise, you should always try the hi-flow cat first before chopping and changing the mufflers to a louder one (normally the smaller body size mufflers are louder than the large body ones.). This may save you a lot of money, time and hassle. The reverse can also be applied here for a quieting a system (at the cost of some power and flow)
Both ceramic and metallic cat converters could fail or “melt” under extreme high temperatures. An example is an engine that runs too rich. The excess amounts of un-burnt fuel can get dumped and trapped on the edge of the cat and continue to burn in a very high temperature for a long period of time, which could cause the cat substrate to melt.
The above example is often seen on a dyno runs with newly installed cat (especially with other power supporting modifications). So Extra precaution is required and a must when dyno running a car. Always make sure the air/fuel mixture is right or within reasonable range before a max power run. Maintaining a good engine tune is crucial for the longevity of the cat converters. It’s also important to note that many cat converter manufacturers do not cover warranty for failure due to incorrect engine conditions.
Important note: XFORCE hi-flow catalytic converters are designed for off road and racing use only.