CATS

As far as I know you do not have a choice. Only pre 93 cars have the option to remove cats altogether as the emission levels are different in the MOT test. I removed the cats on my 91 850 when I installed a custom stainless system. The sound is terrific but I never noticed any discernible improvement in power levels. Personally, having now lived with this system for a few years I would have preferred to have replaced with a stock system but cost was an issue. The entire stainless system, guaranteed for life was less supplied, fitted incVat than the supply only of the two rear boxes from the dealer. At the time it was a no brainer. The original boxes rotted through at 8K presumably through lack of use.

Worth giving your local MOT station a call.

Regards

No car, not even a new one, has to have a cat fitted to pass the UK MOT test. This is a popular misconception.
However, before you all go out and throw yours into the nearest heavy metal recycling bin, there is, of course, a catch.
The emissions test for a car new enough to have a cat fitted will be much, much stricter than for a pre-93 car without a cat requirement.
You will definitely struggle to get your car through this emissions test without a cat.
I don't know if it's possible to do it, someone else can answer that bit, but be warned.

Hope this helps!

You're right same rules apply here in Holland.

Peter

but the emmissions test is part of the mot, is it not

Yes, I think all you have to do is make sure you pass the test. Cats are one way. Can't think of another though.

Just had a chat with my friendly MOT man. The problem lies with the preprogrammed information in the computer. As soon as your car details are entered it comes up as either a Cat test or Non Cat test and the emission levels are pre-set. To his knowledge there is absolutely no way to bypass this procedure. However, there is apparently the possibility of a relaxation for modified vehicles whereby a test can be done 'as presented' in which case a Non Cat test can be carried out. On the back of the VOSA form there is a number that can be called to check your status. It was suggested that an explanation of the problem with the Ministry might get you a relaxation. It sounds like a bit of a long shot and it is likely that a compelling argument will be needed.

Hope this helps, good luck

The “As presented” scenario sounds very interesting.
If anyone manages to get a post ’93 car, minus cats, through an MOT using this route could they please let us know.
My cats and exhaust have done 100k – still ok, but can’t have much longer, surely? – and a non-cat bespoke replacement system could be very tempting in terms of cost.

I have removed cats on less exotic cars (pre-93) and the ECU simply adjusted itself to suit.
MOT’s were no problem. Performance increase could me measured, but not felt – so marginal.
Ah – those were the days! Not so good for the environment though I suppose.

I actually think the whole cat issue is overstated. The emissions from my non cat 850 are so low they barely represent 1% of the allowable limit. Also, cats apparently don't work until the system reaches a working temperature so half of those people on the school run, shopping trips and short commutes don't make any difference anyway!!

Hi all,

I was wondering what the reason is for the cats to go bad. Do they get clogged with dirt? That is, all the the stuf that is not supposed to go into the air. If so, can the cats be cleaned and reused?
Just a small thought.

Peter

Most cats are made of a fine ceramic honeycomb matrix covered in noble metals like platinum, which act as catalysts for chemical reactions. The total surface area is roughly equivalent of a football pitch. If not from normal wear, they can fail for the following reasons:

1.) because of old age the metal canister rusts and disintegrates (some are stainless)
2.) wrong fuels, oils or additives are used in the engine which contaminate the catalyst.
3.) incorrect ingnition (pinking) which can shatter the ceramic core.
4.) Driving through water with hot exhaust can cause thermal stresses and cracks.
5.) manufacturing defects (some MB cats have failed in less than 5k miles)
6.) mechanical shock from a knock or bump, causing ceramic core to break.
7.) engine running too rich with too much unburned fuel can make the catalyst burn out. Too may failed starts can be bad due to flooding the engine and then the cats.

Typical life is around 60kmiles, as they will eventually get coated and contaminated, losing their effectiveness. On older cars like the 8 series, the cat is far down the exhaust, but common practice now is to place the cats near the exhaust manifolds so that they warm up and activate quicker. This produces sharper thermal stresses and thats why these used to fail more commonly in the early days.

The exhaust is a resonant system and with a broken ceramic cat, particularly with those near the exhaust manifolds, there is a danger of the engine sucking in ceramic dust and particles, which is obviously a bad thing. So, you should not drive with broken cats.

If the can rattles when tapped with a rubber mallet or with the engine running, you hear a rattling sound as if the can is filled with loose nuts and bolts, it's a sign that the core is damaged.

The catalyst is not a particulate filter; it's a surface for chemical reactions to complete the burning process of unburned fuel and gasses. Such that unburned hydrocarbons are oxidised and CO is convertered to CO2 and NOx is reduced. (Any soot or dust that clogs it up will prevent it working)

CO sensors before and after the catalyst give information to the fuel managment system (engine ECU) to control the amount of fuel injected to reduce CO (to get Lambda=1).

Arnie,

Thanks for that. I'm still learning every day

Peter

Excellent details above.
Catalyst life is indeed hard to predict.
I've known cats that lasted from 5,000 miles way up to 150,000 miles.
Low mileage (particularly due to short journeys) cars can be very prone to condensation, corrosion, expansion/contraction loads and fuel/oil contamination due to engine not running at full temp.
There are cases of cats on test beds (constant running) that have lasted more than long enough to have taken you on several trips to the moon and back.

All of which is no comfort if yours are scrap!
Hope a solution can be found.

You could always chop out the old ones and weld in a pair of universal one's. They will do exactly the same job for a fraction of the price.

have you looked here? :-

http://www.larinisystems.com/catalogue.php

I wish i had seen those prior to my replacements