Safe Speed Forums

I was having a bit of a whinge about catalytic converters the other day, basically the mid section of the exhaust on my Legacy (ie. the bit with the cat in) has rusted at the far end, right by the flange, and Subaru want something like £400 for a new one, this is on an 8 year old car.

Now ok, on the Legacy I don't mind paying that, but I also own a perfectly good 1991 Volvo that cost me £180 and has a cat in the exhaust too. If the exhaust rots on that thing, instead of costing me £50 for a bit of cheapo pipe it's going to cost me double what the car is worth and end up scrapping the damn thing, may as well buy a new rusty shed with a few years of life in it.

Surely that can't be good for the environment.

Then my GF chirps in by pointing out that all the heavy metals that exist in a cat will do far more damage to the environment once I throw it away than all the CO2 that my car would be chucking out without the thing fitted. Not to mention that energy is expended pushing the exhaust gasses through what is effectively a metal sponge, therefore increasing fuel consumption.

I've since discovered that my car actually has another cat in the downpipe, so in order to do my bit for the environment, I am replacing the centre section with a bit of fancy metal drainpipe from Hayward&Scott that's 1/3 the price.

What's the betting that the greenies wont see it that way though? (also if this is illegal or incorrect, please let me know and I wont do it. I still expect to pass emissions come MOT time)

I'm damned if I can remember where but I think I saw some analysis once that trounced the myth of keeping an old car for a long time being better for the environment than buying a new one. (obviously on a like-for-like) car type basis! Don't get me wrong, as my pride & joy is a 17 year old pre-cat 3 litre, I'd LOVE it not to be the case but those were the results! I've a feeling that 7 years (on average) was about the break-even point.

As far as the legality of removing the centre cat goes,you MIGHT get away with it. Technically, it would be illegal but nobody ever checks other than for the MOT which is a much less onerous test than the type approval test. The purpose of the small cat near the manifold is to act as a "starter cat" to get the gas temperature up quickly enough for the main cat to "light up" in time to pass the EC emissions test (which starts at 18 degrees C (I think). Your starter cat (if it's in good condition) might just be enough to clean up the gas to MOT levels without the main cat in place if you're lucky. If your car is new and smart-arsed enough to have a lambda sensor before AND after the main cat though (unlikely) it would put on a warning light if you took the cat out.

AS far as your rust is concerned, I'd have thought that any half-competent welder could sort that out for £50 for you. Obviously, the heat of the welding is unlikely to bother the cat!

I'm not sure the notion that the restriction imposed by the cats is a worthwhile argument. Older / cheaper designs use a ceramic substrate and they were a bit restrictive but most manufacturers used to just cut down on the silencing as some of that was now done by the cat, so there was no net increase in exhaust back-pressure. Newer & more expensive cats use a metal substrate which is much thinner and therefore has a bigger open area. We used to use these at a place where I worked and never saw a difference on the dyno with and without cats - although that didn't stop owners taking them out! Besides all that, your car would only experience a restriction at "full throttle + full revs" when the gas flow in the exhaust was highest. As that's not exactly "eco-driving" anyway, the whole argument is probably somewhat academic!

Cat cars are generally thirstier but that's because engines need to run richer to make the cats work. Overall, fuel consumption (and hence CO2 emissions) would be considerably lower than they are now without the cats but the politicians told us that it was best for us at the time because of all the acid rain and smog. It was "much better" to turn it all into "harmless" CO2. As it is, CO2 emissions and fuel consumption haven't changed as much as they could have done!

Finally, I'm not sure that heavy metal contamination of the landfill sites will be an issue. The metals are so expensive that lots of companies do a roaring trade reclaiming the precious (heavy) metals out of old cats! A slightly different argument is about the amout of energy and CO2 consumed in mining and processing those metals in the first place and the environmental damage it does in the process - but hey, that happens in countries that are full of poor people so as long as it's not on OUR doorstep, that's OK!

In my car, the cat I'm on about is in the downpipe after the primary turbo. I'm not sure if there's a starter cat in the manifold as well.

I have the added bonus that there is no such cat in the downpipe from the secondary turbo, but that one only comes into play above 4000 RPM

I only have one lambda sensor, it's in the manifold and accessible through the front left wheelarch (handy since the damn thing is constantly failing) so no worries on that part.

Are you suggesting that after removing the cat, I could run a little leaner and therefore save fuel (and by extension the planet!)?


In any case, I was planning on doing an LPG conversion in the future, apparently you don't need a cat at all then, since the emissions are so low.

Is that actually in the C&U regulations for vehicles manufactured after a certain date? I thought the only legal requirement was to meet the specified maximum emissions for the model year in question.

My vehicle already breaks C&U regulations as it is fitted with (factory) HIDs but no self levelling or cleaning mechanism. (it does have a manual adjuster, which I check from time to time or when carrying heavy loads)

To import it, the previous owner replaced the factory HIDs with standard halogens which got it through the ESVA test, it then went on to fail it's MOT at the dealership I was buying it from because some muppet had bypassed the HID system and put halogens in! They had to put the HIDs back!

I've pretty much given up at this point, and come to the conclusion that C&U probably doesn't apply particularly well to this car, I also know for a fact that there is no emissions data for it, so I have to pass the "generic CAT test" emissions level, which even my GFs H reg Nissan 200SX with no cats at all and heavily modified is able to meet!

Most modern cars have at least two cats. One near to the exhaust manifold and one further downstream. The one nearest to the manifold is usually smaller and is called a “warm up” cat. It works almost as soon as the engine is running from cold. The one further downstream is the main cat. A car can pass an MOT without the warm up cat working (I can say from experience).

As far as the environment is concerned cats are a disaster. Not only because of the resources used in the manufacture but also because they INCREASE carbon dioxide emissions. There was a lot of development in lean burn technology in the UK which would have been significantly better than catalytic converters but the stupid politicians wanted to go the catalyst route and since catalysts cannot be used with lean burn the research was abandoned.

_________________
Speed camera policy Kills

Yep, remember that was one of the big "selling points" when they were introduced: "Look, they take carbon monoxide and change it into perfectly harmless carbon dioxide."

Now people in the same places who were saying that talk about CO2 as if it's the most noxious substance known to mankind.

C&U deals with anything that could be used on a public road so it contains quaint stuff about steam engines needing a tray to catch cinders & so on. The emissions regulations are quite extensive but they have a big table which lists all sorts of categories of vehicle and their dates of first use and then refers to one or other EC Directive on emissions. Now it doesn't actually require them to meet the Directive emissions levels once they are "in-service", but it obviously needs them to meet the "MOT" levels.

Regulation 61, paragraph 7 states:

"(7) Subject to Paragraphs (8), (9) and (10), no person shall use, or cause or permit to be used, on a road a motor vehicle to which an item in Table II applies if, in relation to the emission of the substances specified in Column (6) of the item, the vehicle does not comply with the requirements relating to conformity of production models specified in
Column (4) unless the following conditions are satisfied in respect to it–

(a) the failure to meet those requirements in relation to the emission of those substances does not result from an alteration to the propulsion unit or exhaust system of the vehicle,

(b) neither would those requirements be met in relation to the emission of those substances nor would such emissions be materially reduced if maintenance work of a kind which would fall within the scope of a normal periodic service of the vehicle were to be carried out on the vehicle, and

(c) the failure to meet those requirements in relation to such emissions does not result from any device designed to control the emission of carbon monoxide, hydrocarbons, oxides of nitrogen or particulates fitted to the vehicle being other than in good and efficient working order."

I'm not a lawyer but I think this is a spectacularly tedious legal way of saying you can't take your cats out if it might cause the vehicle not to meet the Directive requirements that a vehicle of its age and type were supposed to meet"!

That's why I was saying "technically illegal"! In reality, they only way they're ever going to check is with MOT equipment and even though the car might not meet the Directive requirements, it could possibly meet the MOT requirements with a warm engine!

I guess in theory, yes! In practice, I don't know how you'd weaken the mixture off without re-mapping it and it would be a brave chap who tried that higher up the power output because I'd imagine horrible things might happen to pistons and valve gear if you werent careful!

I run my Tomcat with a de-cat tube in place and keep the cat in oil-paper for MOT's. My ECU remaps itself to a leaner burn with the cat off, as the level of hydrocarbons rises in the exhaust gas. As a result, I use less fuel and get more power running catless.

_________________
Aquila



Licat volare si super tergum aquila volat...

The point is you do not throw it away. You have it recycled, thus the heavy metals are recovered. That's the theory...

_________________
www.thatsnews.org.uk / www.thatsnews.blogspot.com / http://thatsmotoring.blogspot.com/

Worth about £25 to a scrap metal merchant...

_________________
Aquila



Licat volare si super tergum aquila volat...

That's odd! Do you have 2 lambda sensors, one either side of the cat? I'm not familiar with the Tomcat but I thought most UK cars of that era only had one sensor and it was BEFORE the cat - in which case, I can't see how the sensor would "know" that the cat had been removed!

Surely the lamda sensor measures the amount of oxygen in the exhaust, so removing the cat in a 1 sensor system should make little difference.
In any case, the co2 in the exhaust increases in a cat-equipped car. You should also note that roadside exhaust measuring is being rolled-out soon...

Talk about convoluted wording! I had to read that slowly about four times, but I think I'm coming to a similar conclusion. Modifying the exhaust is clearly legal if the emissions still fall below the specific type approval levels. I guess the question comes as to whether those type-approval limits are stricter than those imposed by the MoT inspection.

As you say, I think in practice nobody is likely to question it so long as emissions are within the MoT limits.

It's like the lighting regulations (with which I'm far more familiar) and the daft rule that on post-1986 cars all bulbs used in external lamps must have a BS/Euro approval mark. Technically that makes most of the external lights on my '87 Ford illegal, but who the heck is ever going to ask to look at the bulbs? (Besides, technically they fall foul of the C&U lighting regs. on about four or five other more obvious counts anyway.)

What happens is that removal of the cat increases air flow through the engine. The lambda sensor is part of a closed loop control system that compensates for the increased gas flow through the engine. It is not 100% as there is usualy part of the engine map that is not closed loop such as during rapid engine speed changes, the airflow meter has to work alone in this case so you could get some leaning out with the increased air flow.

Back in the day of the BRSCC Fiesta Challenge race series they had to run cats. The usual trick was to run the engine with a spark plug lead off during a practice session. The fuel from the cylinder would burn in the cat and erode the core. It was good for another 10 hp if done right.

_________________
Speed camera policy Kills

I doubt very much if that is correct. Shame that you can't remember as I'd really like to read it.

My understanding of the two lambda sensor systems is that they're an american requirement on all OBD II card (96 onwards?) and that the second one is only there to turn on the CEL if your emissions are bad (or more commonly, because the second lambda sensor has failed). American emissions testing stations rely on the output of this sensor and just use an OBD II reader to "check" emissions.

Therefore it's common practice to unplug the second lambda sensor and jam a resister into the connector rather than fixing it.

In any case, looks like my plans are legal, so long as the emissions aren't too bad, if it fails, I'll just have to put the old exhaust back on (after a trip to the welders) and ebay my new one.

Oh yes!!!! ...and then some!



Aye, the equipment used for the type approval tests is so complex (and expensive) that I don't suppose anyone would ever be caught, and the MOT / Roadside Check stuff will be nowhere near sophisticated enough to check in sufficient detail.

I'm struggling to get my head round that one still!
I can see how taking the "brick" out of an old style ceramic cat on a poorly designed system could allow the engine to flow more gas - assuming the cat was the bottleneck. But I could only see how this could happen under full throttle-full speed conditions when gas flow is highest and under those conditions surely the engine would be running "open loop" anyway?