cat removal and the law?
Discussion
Cars designed to run with cat's wont ever pass an MOT without one firstly. Its also pretty obvious by the smell when you are behind a car without the cats fitted due to the stink of the hydrocarbons,(or as any copper with a nose could tell you) so I would not want to argue in court that I knowing made my car an MOT failure by removing the cat's (just my opinion). Removing the cat's only reduces the back pressure slightly, and the car will still run the catalyst fueling patterns thats designed around emmisions, not performance, so basically taking the cats out on there own has a very limited effect to performance. You could just get a high flow catalysts instead, and forget all the bother of worrying about each MOT.
Boosted LS1 said:
My saab usually passes the mot with the cat removed and it's definately quicker and more responsive minus the cat.
Any turbo-charged car is likely to see a noticeable improvement from removing the cat, simply due to the reduction in back pressure on the turbo.Later Evos run extremely cleanly (around 2 ppm against a limit of 200 ppm) with a cat in place, I wonder if someone has managed to get through the test without one?
As for sports cats, they're all well and good, but they also cost several hundred pounds, a decat pipe costs between £30 and £60 for a lot of cars.
blitzracing said:
Cars designed to run with cat's wont ever pass an MOT without one firstly. Its also pretty obvious by the smell when you are behind a car without the cats fitted due to the stink of the hydrocarbons,(or as any copper with a nose could tell you) so I would not want to argue in court that I knowing made my car an MOT failure by removing the cat's (just my opinion). Removing the cat's only reduces the back pressure slightly, and the car will still run the catalyst fueling patterns thats designed around emmisions, not performance, so basically taking the cats out on there own has a very limited effect to performance. You could just get a high flow catalysts instead, and forget all the bother of worrying about each MOT.
Several inacurracies in your statement.Cars designed to run cats can pass the MOT withpout having a cat fitted, theres nore to emission output than a cat.
What smells worse hydrocarbons or the 'bad egg' smell you get from a catalyst car? And hydrocarbons aren't that discernible.
The way a cats removal affects a cars fuelling and performance can depend whether the cat is infront of or behind the lambda sensor.
High flow cats cost mega bucks and if with a de-cat the car will pass an mot thats ok. Remember an mot is only good for the exact time the car was tested.
youngsyr said:
Later Evos run extremely cleanly (around 2 ppm against a limit of 200 ppm) with a cat in place, I wonder if someone has managed to get through the test without one?
I know of a couple of modified Japanese turbo cars that have a switchable "lean" fuel map in the aftermarket ECU for "economy" according to the owners. This also passes the MOT emissions test without a catalyst according to the same owners.I would not comment on how often this map is selected in normal use.
Bucket O Frogs said:
Is Blitzracing a councillor or the plod??
Sounds like the kind of ill informed BS that would come spilling out of the mouth of a brain washed retard
Now now!Sounds like the kind of ill informed BS that would come spilling out of the mouth of a brain washed retard
You are getting him mixed up with SCP employees!I'd guess he just applied limited experience of the subject to a broad spectrum of non conformists who have found otherwise!
It used to be common for young drivers to take out cats in an attempt to improve performance around my nephew's locale, with varying degrees of success. He in turn benefited from selling the redundant cats on ebay!
As a means of reducing pollution, I'm led to believe that cats are not as good value as other methods adopted by major manufacturers, who would be glad to see the back of them in their newer models... is that true?
Both Volvo and Honda made engines capable of passing US tests without cats, prior to 2006 apparently.
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.
Best wishes all,
Dave.
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.Best wishes all,
Dave.
Any vehicle that is fitted with a cat runs a fuel system known as close looped; that is, the exhaust gases are constantly measured as near the engine as possible by a lambda sensor. The signal from the lambda is utilised by the ECU (electronic control unit), to constantly adjust the fuel to air ratio and keep it within set limits according to engine temperature.
It is the fuel control system that determines the emissions, NOT the cat. The cat cannot control or influence control of the emissions, it simply cleans up the residue after combustion.
With regard to the MOT test; this is carried out at idle speed at which time the exhaust gas flow is so low that the cat virtually does no work. If you have a vehicle that has high emissions at idle without the cat, you have a fuelling problem.
Now some of the Japanese cars I have seen depend on the cat at idle to clean up the exhaust output: this is bad design, and will drastically reduce the life of the cat.
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.
I keep my exhaust with a cat in the shed, it only gets put on to the car for MOT's, never had a problem when the police have looked at it, once i explain that yes i have my MOT, and my cat is at home and can be fitted easily they ignore it. It is always worth remembering that an MOT is almost completely worthless by midnight.
And for the record my car wouldn't pass an emissions test at idle, it fails by a tiny amount, and only just passes with the cat on thats the mapping it is a Jap Turbo it runs rich. But it still fails by much less than my old housemates car, eurobox with a cat fitted, failed by last year.
And for the record my car wouldn't pass an emissions test at idle, it fails by a tiny amount, and only just passes with the cat on thats the mapping it is a Jap Turbo it runs rich. But it still fails by much less than my old housemates car, eurobox with a cat fitted, failed by last year.
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.Best wishes all,
Dave.
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