Catalytic converters

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How they work

Short version:
It takes the O (oxygen) from the NO (nitrogen oxide) and puts it on the CO (carbon monoxide) to give CO2 (carbon dioxide) and N2 (nitrogen gas). CO is harmful, NO causes acid rain etc. CO2 and N2 are not harmful. It also breaks the HC (hydrocarbons, unburnt fuel) down to make H20 and CO2. HC causes smog etc. The substance in the cat is NOT cat fur (contrary to popular belief) it is some sort of ceramic mesh coated in a Platinum/Palladium alloy. The definition of a catalyst is a chemical that assists a reaction but doesn't get used up in the reaction. Kind of like women and spending money.

Long version:


Catalytic converters were fitted to minis from the early '90s. They were standard fit from the 1990 Rover Cooper introduced July 1990 and an optional extra on 998s from chassis 426525 in June 1989.

The MoT checks the exhaust emissions level, not the presence of the cat, so you can remove the cat from carb'd minis and still get through the emissions. A special link pipe is available (costs about 17UKP, made by Maniflow) to replace the cat.

Some fuel injected minis (>1995) have to pass stricter emissions and it is very difficult to pass these without the cat, so removing the cat is not advised. However, it is based on the VIN number and/or engine number.

"If the 4th & 6th character of the VIN are 'X' & 'N' respectively and the 8th character of the VIN is 'Y' then if the VIN serial no. (last 6 digits) is 060880 (from memory:) your car will have to undergo the CAT test, otherwise it's tested just like any non-CAT Mini - i.e. 3.5% CO and 1200 ppm HC - a doddle for the SPi :)"

Note that this information is only valid in the UK, and you are advised to check the law in your country/area before removing the cat. Most friendly MOT stations have a book which tells them which VINs do and don't need a cat.

Is a CAT Required (UK Regluations)

Minis from 1995 (introduction of injection) MUST have a catalytic converter fitted to pass the MOT, and must be under 0.5% CO and 200ppm HC.

Cars registered before then (uk 1994 M reg or before) do not have to have a cat fitted, and must be under 3.5% CO and 200ppm HC.

For cars right on the borderline (eg: an M reg 1994 mini 35 LE) you need to look at the chassis number. A typical number is "SAXXNYADBBD090825". The important bits are the 2nd "X" and the 1st "D". Those denote that the car is cat exempt. If you do not have the X and D then you will need the cat to pass.

Broad Summary:

1990s cat/inj : 0.5% 200ppm

1990s no cat : 3.5% 1200ppm

1980s : 4% 1200ppm

Article by Scott Beavis following CAT woes with "Bilbo"

Emissions for Passenger cars:

First used before 1/8/1975 - Visual test only. Failure for excess idle
speed, dense blue or black smoke for 5 seconds at idle or during
acceleration up to 2500rpm or half engine max speed whichever lowest.

First used between 1/8/75 and 31/7/86 - meter test CO <=4.5%, HC<=1200ppm.

First used between 1/8/86 and 31/7/92 - meter test CO<=3.5%, HC<=1200ppm.

First used between 1/8/92 and 31/7/94 - advanced emission test (CAT) if its
running on petrol when presented, to the vehicle specific limits usually
around CO<=0.3%, HC<=200ppm and Lambda 0.97 - 1.03.

Remember from 1st August 2001 a basic emission test will be carried out initially.

above from




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