My two cents, and a few points.
I gather from the USA forums that BMW tend to have much larger than normal cats to reduce restriction problems.
The lifespan of a cat is not much over 100000Km, much less here in SA.
My 540i cats died, removed them and the power gain was quite significant. I did not expect this from the above.
Fuel in SA is real sulphur contaminated crap. Every cat equiped car I drive behind stinks of sulphur dioxide. (Rotten egg smell, and a highly toxic gas. Basically the lousy fuel killing the cat by contaminating it with sulphur) Catalytic converters are very clever devices, but are very susceptible to contamination by lead, LRP, silicone, antifreze and any non perfect fuel. I would take a guess that in SA if your car has more than 80000Km on, the odds are your cat is probably past it's usefull life anyway.
LRP kills cats (Only a tank or two of LRP with MMT contaminates the cat with Manganese rendering it useless forever)
Cats cannot be cleaned by taking the car for a hard drive at high speed, this is a total myth. If it's dirty it's dirty forever.
On an OBD II car (post 98) a bad cat will give a check engine light and the owner will probably try to replace a post cat O2 sensor for nothing instead.
You can remove cats on an OBDII car, but you will need an O2 sensor fooler. OBDII cars have a second O2 sensor after the cat that monitors the quality of the gas coming out of the cat to check whether it's working.
Cats can be removed easily on an OBD I car (pre 98 with no check engine light) with no problems.
The only way to tell a blocked cat is to measure the pressure upstream.
Using unleaded without a cat emits more poison into the atmosphere than the old leaded fuel.
I do not like cats at all, it is a concept that has merit in places like California and parts of Europe, here in SA we have too few cars to fully justify their use. I think cats are just a big $ making and window dressing scheme here.
opcorn:
