MINI Cooper R56 N12-engine decat

The R56  N12 MINI’s are known for their catalytic converters coming loose inside the housing attached to the exhaust manifold, and dropping down. Instead of replacing the complete exhaust manifold, the catalytic converter can be removed, or as generally referred to: decatted.

Poor performance and a lack of power are tell-tale signs of the cat coming loose and dropping down. To check if this is the case, the oxygen sensor after the cat is removed. If you are able to see the light grey catalytic converter when peeping inside the hole where the sensor would be, it’s time to decat.

The exhaust manifold is removed from the vehicle. Using a very thin grinding disc, a window is cut in the housing. The perished cat is removed through this opening, and the housing is welded closed again. As can be seen, the catalytic converter has started breaking up and burning away in some areas. It’s supposed to be perfectly squared up openings, all flush on top and open all the way through from front to back.

When decatting, software upgrades are required. This is basically recoding the software in order to prevent the engine management light from coming on. The oxygen sensors are refitted, so if the software is not upgraded, the original software will detect the cats have been removed and bring on the EML (engine management light). It’s important to remember that the cats’ job is to filter gasses emitted from the engine through the exhaust. With it removed, there is a possibility that a small amount of smoke would be more visible from the exhaust, but this is not always the case. If the engine is sound, this would not be a concern. However, as is the case with many high mileage engines, a bit of smoke may be visible. The sound from the exhaust is virtually the same as before. However, the performance improvement is notably different.