cat removal and the law?

[cambiker71]

In fifteen years or so of MOT testing i've yet to find a car without a cat (that had one fitted originally) that is anywhere near the test limits to pass, either at idle speed or the raised engine speed specified for the test, when a good cat is refitted then the emissions are drastically reduced to well below the pass limits in my experience.
VOSA do the roadside checks, i've not seen one carried out but apparently they can do roadside emissions checks too and could issue prohibition notices.

[cambiker71]

blondini said:

p1esk said:

I was recently talking to an experienced motor engineer who runs a small repair shop and does MOT tests. He reckoned that if our 406 HDi needed a new exhaust system, and I were to fit one without a cat, it would still pass an MOT emissions test. Now I don't know whether he's right or wrong, but certainly the idea is quite appealing on cost grounds alone, apart from any possible gains in performance or fuel economy.

Best wishes all,
Dave.

He's right because the only mot emissions check on diesels is for visible smoke. Those emissions which would be reduced by cats are not tested.

It's a measured check rather than visible smoke, I have no idea what exactly is measured or what the measurements mean but the limits can be found by searching this link which is an online version of our testers manual.

http://www.motinfo.gov.uk/htdocs/index.htm

[Robert060379]

I was told that if you are pulled over for whatever reason and the officers look and see a "de-Cat'" pipe then the car can be ordered to have a IVA or M.O.T test within two weeks. "Section 59" is it causes any undue distress.

[Fish981]

jith said:

p1esk said:

I was recently talking to an experienced motor engineer who runs a small repair shop and does MOT tests. He reckoned that if our 406 HDi needed a new exhaust system, and I were to fit one without a cat, it would still pass an MOT emissions test. Now I don't know whether he's right or wrong, but certainly the idea is quite appealing on cost grounds alone, apart from any possible gains in performance or fuel economy.

Best wishes all,
Dave.

Well Dave, here is another experienced motor engineer telling you exactly the same thing. This issue comes up here fairly regularly and is always completely misunderstood.

Obviously.

jith said:

Any vehicle that is fitted with a cat runs a fuel system known as close looped;

Unless it's a diesel, like the 406 HDi you're quoting.

jith said:

With regard to the MOT test; this is carried out at idle speed

Wrong again, it's also carried out between 2.5k and 3k. On a petrol car anyway.

jith said:

at which time the exhaust gas flow is so low that the cat virtually does no work.

Rubbish.

jith said:

For the police to check emissions at the roadside they would have to have a CO meter, and I have never seen this in any police vehicle nor heard of it. It would be more likely that VOSA inspectors would do this. I would also be unsure as to what they would charge you with.

For a first offence you'd probably get a vehicle rectification notice.

[nikaiyo2]

Quite a lot of import cars can run without cats, anything built until Aug1995 (iirc) that does not have an EXACT match in the VOSA handbook is tested to the Pre- Cat limits.

So R32 skylines, all non Turbo R32-33 Skylines, Mr2 Turbos Galanza's, should imagine a lot of US imports, pretty much anything that was NOT sold new in the UK by the manufacturer.

HTH

[Mr2Mike]

naffa said:

The way a cats removal affects a cars fuelling and performance can depend whether the cat is infront of or behind the lambda sensor.

If there is only one lambda sensor it will ALWAYS be in front of the cat, closed loop fuel control could not possibly work if it was after the cat. On OBDII equipped cars there will be a sensor before and after the cat, the later one purely to monitor the effectiveness of the cat itself rather than to control fueling.

[Mill Wheel]

Cats are responsible for increased greenhouse gasses, according to Wikipedia, getting rid of carbon monoxide, at the expense of nitrous oxide and carbon dioxide released back into the atmosphere!

Didn't Volvo introduce a catalytic radiator at one point which cleaned up Carbon Monoxide from the air passed through the radiator?

[jith]

Fish981 said:

jith said:

p1esk said:

I was recently talking to an experienced motor engineer who runs a small repair shop and does MOT tests. He reckoned that if our 406 HDi needed a new exhaust system, and I were to fit one without a cat, it would still pass an MOT emissions test. Now I don't know whether he's right or wrong, but certainly the idea is quite appealing on cost grounds alone, apart from any possible gains in performance or fuel economy.

Best wishes all,
Dave.

Well Dave, here is another experienced motor engineer telling you exactly the same thing. This issue comes up here fairly regularly and is always completely misunderstood.

Obviously.

jith said:

Any vehicle that is fitted with a cat runs a fuel system known as close looped;

Unless it's a diesel, like the 406 HDi you're quoting.

jith said:

With regard to the MOT test; this is carried out at idle speed

Wrong again, it's also carried out between 2.5k and 3k. On a petrol car anyway.

jith said:

at which time the exhaust gas flow is so low that the cat virtually does no work.

Rubbish.

jith said:

For the police to check emissions at the roadside they would have to have a CO meter, and I have never seen this in any police vehicle nor heard of it. It would be more likely that VOSA inspectors would do this. I would also be unsure as to what they would charge you with.

For a first offence you'd probably get a vehicle rectification notice.

What is it about this site that attracts every foul-mouthed, ignorant, pedantic "expert"?

I write on many sites and give my advice free and with a good heart and never have this kind of crap to deal with.

I don't know who the hell you are and care even less, but you could do us all a favour and crawl back into your hole. But before you do, and for your information.

I have almost 40 years experience as a qualified motor engineer. This includes project design work on all kinds of vehicles. I am fully aware of the functions of all catalyst systems and also the MOT regulations.

I was not specifically referring to Dave's car, but was talking in general terms. Anyone with half a brain would be able to see this. The MOT test is carried out at normal idle speed and then at approximately 2500 RPM, a FAST idle. It is NOT carried out under any significant load, or on a rolling road, or in gear. In other words, it does not give a detailed picture of the state of the fuelling system.

This is a link to another post on the same subject on the Classic Car forum:-

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Read it and learn something.

I am in the process of restarting my classic and performance car business and I will be advertising on this site. You will then know exactly who I am and where you can contact me. If you want to discuss any points of a technical nature you are welcome to visit my workshop and do so face to face; I suggest you know exactly what you are talking about before you do.

[Pigeon]

Mill Wheel said:

Cats are responsible for increased greenhouse gasses, according to Wikipedia, getting rid of carbon monoxide, at the expense of nitrous oxide and carbon dioxide released back into the atmosphere!

Not nitrous oxide, one of the functions of the cat is to get rid of oxides of nitrogen. Said oxides are produced in the cylinder as an unwanted byproduct of the combustion process, as the heat of combustion causes some of the nitrogen in the air to react with oxygen. The problem is worse with lean mixtures as there is more "spare" oxygen around.

Cats do oxidise carbon monoxide and hydrocarbons to carbon dioxide, but it's doubtful if that can really be counted as "increasing greenhouse gas emissions" since the CO and HC are only there as a result of "imperfections" in the combustion process, and represent wasted energy; in an "ideal" engine they would not be there, but life's not like that

Cats do however increase CO2 emissions in a more "genuine" way by making the engine less efficient. For one thing they cause a restriction in the exhaust which increases pumping losses and interferes with exhaust tuning. For another they require that the engine be run at the stoichiometric point which is not ideal for efficiency; the most economical operation is achieved by running the engine slightly lean at part load.

Mill Wheel said:

Didn't Volvo introduce a catalytic radiator at one point which cleaned up Carbon Monoxide from the air passed through the radiator?

I do remember hearing about some proposal like that, not sure who it was from though - my vague memory is it wasn't a manufacturer - and I'm not sure it ever made it into production... strikes me as being something that a manufacturer would be unlikely to introduce unless compelled by legislation, since it increases the cost of the car without providing any noticeable benefit to the average buyer of said car.

There was of course Saab's publicity stunt with their Trionic engine management system where they fed the exhaust of an old Saab two-stroke into the intake of a modern Trionic-equipped car; initially the emissions shot up, but once the electronics had worked out what was going on they returned to normal.

jith said:

This is a link to another post on the same subject on the Classic Car forum:-

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Read it and learn something.

I was just about to link to that myself

The basic emission characteristics of an engine are determined by the efficiency of the combustion process, which is influenced by such things as combustion chamber design, crevice volume, charge turbulence, and precision of control of fuelling and ignition timing. Cats merely compensate for inaccuracies which prevent combustion from being fully optimised. They were originally introduced when the vast majority of cars had carburettors and points ignition, giving pretty imprecise control, and design of the combustion chamber and related matters still involved a lot of "suck it and see" and whether or not the resulting design gave thoroughly complete combustion or just "good enough" involved a lot of chance.

At the time they became a legal requirement in the UK it was still the case that most cars used fairly simple ignition and fuelling systems, which weren't capable of the performance of modern ones, and combustion chamber designs which were mostly still pretty old - such naturally good performers and such good management systems as jith refers to in the linked post being the exception rather than the rule. Since then such factors as the increasing availability of sophisticated computer simulations of engine behaviour and the combustion process, plus the legislative pressure to make use of their capabilities, have resulted in much better combustion chamber designs, and engine management systems also have become much more capable. The result is that there are now a lot of engines around which are perfectly capable of meeting the MoT requirements without the cat (as long as they haven't been buggered around with) and are only fitted with cats because the regulations haven't caught up with the advances in technology.

[RB Will]

Last time I had my Impreza MOTd. I tried it without the cat. It passed all of the criteria but was 0.2% too high with the CO2 so close but no cigar.

On my old scoob I had a miltek exhaust all through on it. on the downpipe (decat) it had a little plate welded on that said this is not for road use. Would that make it illegal?

[youngsyr]

RB Will said:

Last time I had my Impreza MOTd. I tried it without the cat. It passed all of the criteria but was 0.2% too high with the CO2 so close but no cigar.

On my old scoob I had a miltek exhaust all through on it. on the downpipe (decat) it had a little plate welded on that said this is not for road use. Would that make it illegal?

Can't see why it would, I believe that's mainly there to protect the supplier/manufacturer as I believe they can get in to trouble if they sell unroadworthy parts to customers and market them as being roadworthy (or do not explicitly state that they aren't).

Edited by youngsyr on Wednesday 7th April 12:11

[Marf]

youngsyr said:

RB Will said:

Last time I had my Impreza MOTd. I tried it without the cat. It passed all of the criteria but was 0.2% too high with the CO2 so close but no cigar.

On my old scoob I had a miltek exhaust all through on it. on the downpipe (decat) it had a little plate welded on that said this is not for road use. Would that make it illegal?

Can't see why it would, I believe that's mainly there to protect the supplier/manufacturer as I believe they can get in to trouble if they sell unroadworthy parts to customers and market them as being roadworthy (or do not explicitly state that they aren't).

Edited by youngsyr on Wednesday 7th April 12:11

"Not for road use" is something usually printed on/attached to modifications sold into the US market.

[road_rager]

for what it's worth........ my Forester Turbo passed it's last MOT ok with the CAT removed

[youngsyr]

Marf said:

youngsyr said:

RB Will said:

Last time I had my Impreza MOTd. I tried it without the cat. It passed all of the criteria but was 0.2% too high with the CO2 so close but no cigar.

On my old scoob I had a miltek exhaust all through on it. on the downpipe (decat) it had a little plate welded on that said this is not for road use. Would that make it illegal?

Can't see why it would, I believe that's mainly there to protect the supplier/manufacturer as I believe they can get in to trouble if they sell unroadworthy parts to customers and market them as being roadworthy (or do not explicitly state that they aren't).

Edited by youngsyr on Wednesday 7th April 12:11

"Not for road use" is something usually printed on/attached to modifications sold into the US market.

I'm aware of that, but Milltek is an English company and don't have much of a presence, if any, in the US.

I seem to recall discussing this with someone a couple of years back and the conclusion was that a garage could get into trouble for fitting parts that would make a car unroadworthy to a road car when they knew it would be driven on the road immediately after leaving their premises.

If that's the case, I would imagine it would extend to parts fabricators selling the parts destined for road cars via mailorder (such as Milltek).

Perhaps a legal bod could clarify?

[Fish981]

jith said:

What is it about this site that attracts every foul-mouthed, ignorant, pedantic "expert"?

I write on many sites and give my advice free and with a good heart and never have this kind of crap to deal with.

Really? You do surprise me. Still, you get what you pay for.

[jith]

Fish981 said:

jith said:

What is it about this site that attracts every foul-mouthed, ignorant, pedantic "expert"?

I write on many sites and give my advice free and with a good heart and never have this kind of crap to deal with.

Really? You do surprise me. Still, you get what you pay for.

That's true. Tell me what street corner you are on tonight and I'll make sure I avoid it.

[Quaint]

Just to fan the flames a little...

My 928 was registered in May 1991 and although it was originally fitted with cats it has passed the last 3 MOTs without them, and been comfortably inside the emissions limits for pre-August-1992 cars. As stated above, the fuelling system is controlled by an O2 sensor in the exhaust and this (when operating in closed-loop, which is any time other than wide-open throttle) keeps the engine burning very clean.

For cars first registered after August 1992, the emissions limits are much reduced. My car would be under the hydrocarbons limit but over the CO limit, when running with no cats. For cars registered after this date, my understanding is that passing the MOT emissions test is virtually impossible without cats. Happy to be corrected if this is bks.

[drew.h]

Alfatim said:

Whats the situation with removing CATs and the law? I know one needs to be fitted for MOT but what happens when, as many 'may' do, the CAT is replaced with a de-cat pipe?

Are roadside checks done? Is it against the law?

I was worried about this as well. The advice I got was not to worry. If it did fail a roadside test put it down to a lambda problem that you will get fixed. Keep the cat for MOTs though.

[rigga]

Quinny said:

I took my 1994 Griffith 500 for its MOT today... No pre cats and no main cat..

Nothing, just a straight through manifold into a silencer and then out the back

Passed with ease

CO Max 3.50% Mine 0.86%

HC Max 1200ppm Mine 492ppm

No funny business.... Fully legit MOT

Interesting... mines due in the next couple of weeks,still got the dustbin fitted,but i may invest in a decat version if it may be ok without the faff of refitting every year.

[rigga]

Quinny said:

Depressing fact based info

Bugger !