As we all know the CAT is a very restrictive part of the cars breathing system and in the past a way of freeing some locked horse power was to replace the Cat with a small section of pipe (DE-Cat) Most modern cars would still pass the emissions test and no harm done except a little louder. Now worryingly the police state we live in have decided they will outlaw a Decat on the MOT. So i guess this is looked for during the inspection.

My question is if i buy a used CAT from popular online auction can i strip the internals and weld in a straight through pipe with new flanges which externally aesthetically match the old CAT. In otherwords once fitted the from the outside even a trained MOT inspector wouldn't be able to spot the difference. However inside would be a nice clean smooth bore same diameter as the exhaust pipe. I know technically this is still and MOT Failure in principle but in practice surely a visual inspection and an emissions test would be satisfied and no harm done?

If so then i work for a Steel welding company and could get this done a piece of ****. Anyone in the know please confirm if they can see any obvious reasons this would not work. If nothing is preventing this then i will crack on with it and post some pictures of the finished article and get a before and after dyno result.

Without some form of carbon scrubbing material in the exhaust (100-200 cell, high-flow sport cat), it is unlikely you will pass the emissions part of the MOT test.

Without some form of carbon scrubbing material in the exhaust (100-200 cell, high-flow sport cat), it is unlikely you will pass the emissions part of the MOT test.

Whats the reason for this? are they way more stringent these days, I have passed previously with 1.8 Clio 16v (x2), 2.0 Clio Williams, and Cliosport 2.0 MK1 and Cliosport 2.0 MK2 all Decatted. Admittedly that was all pre 2004 so in the last 10 years the tollerance may have come down.

P.S. Thanks for your input. what would be the carbon scrubbing material typically?

That's a fantastic questions for the Ministry of Transport

Regarding carbon scrubbing materials: http://en.wikipedia....lytic_converter

The catalytic converter consists of several components:

• The catalyst core, or substrate. For automotive catalytic converters, the core is usually a ceramic monolith with a honeycomb structure. Metallic foil monoliths made of FeCrAl are used in some applications. This is partially a cost issue. Ceramic cores are inexpensive when manufactured in large quantities. Metallic cores are less expensive to build in small production runs, and are used in sportscars where low back pressure and reliability under continuous high load is required. Either material is designed to provide a high surface area to support the catalyst washcoat, and therefore is often called a "catalyst support".^{[citation needed]} The cordierite ceramic substrate used in most catalytic converters was invented by Rodney Bagley, Irwin Lachman and Ronald Lewis at Corning Glass, for which they were inducted into the National Inventors Hall of Fame in 2002.^{[citation needed]}
  
• The washcoat. A washcoat is a carrier for the catalytic materials and is used to disperse the materials over a high surface area. Aluminum oxide, titanium dioxide, silicon dioxide, or a mixture of silica and alumina can be used. The catalytic materials are suspended in the washcoat prior to applying to the core. Washcoat materials are selected to form a rough, irregular surface, which greatly increases the surface area compared to the smooth surface of the bare substrate. This in turn maximizes the catalytically active surface available to react with the engine exhaust. The coat must retain its surface area and prevent sintering of the catalytic metal particles even at high temperatures (1000 °C).^[15]
  
• The catalyst itself is most often a precious metal. Platinum is the most active catalyst and is widely used, but is not suitable for all applications because of unwanted additional reactions (see below) and high cost. Palladium andrhodium are two other precious metals used. Rhodium is used as a reduction catalyst, palladium is used as an oxidation catalyst, and platinum is used both for reduction and oxidation. Cerium, iron, manganese and nickel are also used, although each has its own limitations. Nickel is not legal for use in the European Union (because of its reaction with carbon monoxide into nickel tetracarbonyl). Copper can be used everywhere except North America,^{[clarification needed]} where its use is illegal because of the formation of dioxin.
  

Thanks for this, Interesting read.

You might want to delete this entire thread if you do it mind.....

posting pics of the evidence is probably not a good idea!

can u guys recommend an exhaust that sounds alittle bit... more fruity without breaking mot regs or the ear drums of people within the car?

Edited 28 January, 201313 yr by Craigt191