Car tuning tips and mods.

The catalyst (also referred to as a pollution or smog control) resides inside the exhaust. Its job is to create cleaner emissions by causing a reaction which reduces the CO2 and NO2 in the exhaust. Because they are constructed of a matrix they impede the flow of exhaust gases and have been blamed by many as power stealers. What options are out there that regain this robbed power?

Primarily there are 2 options to get faster flowing gases through the exhaust:-

The first and easiest is referred to as a de-cat. It is quite simply a pipe that sits where the catalyst should go and effectively the entire catalyst is removed.

What are the drawbacks of  a de-cat? It is illegal in most states and countries unless your car can still meet its stringent emissions requirements without one. Many people swap back the catalyst at the time of the annual test to obtain a roadworthyness certificate but the Police are increasingly using spot checks at the road side to catch people out.

Some engines will also have a probe further up the exhaust from the catalyst and if this reports ‘dirty’ exhaust fumes it will adjust the ignition timing typically running the engine lean. This will result in a loss of power and could even cause the ecu to go into a limp home mode.

The second and most professional option is a sports catalyst. These are manufactured to higher tolerances than the OEM ones and have much better flow characteristics. The drawbacks of the sports cats are usually the cost but in real terms they cost little more than a standard original brand catalyst.

When you put a car on a rolling road what sort of results can you expect to see? Car Tuning Tips took a Mitsubishi Evo IV onto a rolling road and the baseline power with the original catalyst was 295bhp.

With the decat pipe this increased to 305 bhp and then when the sports catalyst was introduced power reached 304 bhp. So we have to conclude that there is very little perfromance difference between a sports cat and a decat. The standard EVO catalyst is actually very good which is why we see little gain between them but on more humble engines power gains reach around 5-10% higher.

If your catalyst needs replacing we would strongly recommend that you source a suitable sports catalyst rather than going for an illegal decat option. If you are using the car off road then the decat would be the sensible and most cost effective option open to you.

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