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How about two cats on one exhaust?

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So I was talking with an independent (non stealership) auto mechanic about my 2000 Polo and told him what a lovely little car it was with a cute little 999cc engine and telling him how good it ran now that I've chucked away about half a ton of plastic and hoses from under the bonnet and he assured me that there's pretty much no chance this car would ever pass it's next MOT because it would fail on emissions even if the engine were brand new as the factory made it because the new MOT rules are basically designed to fail all cars more than an hour and a half old so you're forced to either buy a new car or do without.


After discussing the pitfalls of idiotic, incorrect and pointless emissions regulations like those foisted upon us by the drunken unelected fools of the EU I went away feeling pissed off that the first car I've bought in twenty-odd years was probably just money down the drain as I'd have to throw it away by next year's MOT even though it ran fine. But that got me thinking about some things.


Firstly, I know little of, and care even less about, the science and regulations of modern exhaust emissions but it occurred to me that if a slightly knackered catalytic converter not doing it's job well enough could fail the MOT when nothing else was even wrong with the car then in theory why couldn't you just fit two (or five or ten...) catalytic converters in the exhaust train of your car sequentially so that at MOT time all that came out of your exhaust was fairy giggles and bunny smiles? You could have two exhausts, one made of catalytic converters you fitted once a year for the MOT and a sensible one for real life.


Or how about running bioethanol instead of petrol for the MOT? An enine's an engine and it's not rocket science. They CAN be made to run on a wide range of burny fluids. I've even run a two stroke bike on white spirit and got a 50cc engine to fire up on vodka. In most older engines alcohol or propane will work without much alteration to the carbs, so has anybody tried running a fuel injection engine on something other than Morrison's best supermarket petrol? Just wondering. It strikes me that having cars run on petrol and then making the emissions rules so strict it renders them illegal is pointless and unnecessary.


So, two cats or not two cats? That is the question.


Or how about fitting an enormous bag like a hot air balloon clamped onto your exhaust during the MOT so there's no emissions whatsoever "when tested"?

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I'd stick it in for a test first and see what happens before making any rash decisions. The original cat is big for the size of the engine and has a proper catalyst in it, rather than a cheap nasty euro cat. Emissions standards aren't particularly high for a car that age, so I'd hazard a guess that  as long as its not burning oil or running rich, it will probably be alright. If you want to hedge your bets, just go for a blast so the cat gets hot on the way to the test. 

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I assume this is all in a jokey manner. The test equipment for fairy giggles is made by the same supplier as Irish border alternative technology so you'll be fine.



page 187


shows the criteria for your car model.



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I think:

  • Each cat in the line will have its effectiveness destroyed by free hydro-carbons.
  • You'll need bigger injectors to run on alcohol and stay within the ECU pulse width control window or custom map.
  • Ethanol is aggressive to rubber and absorbs water from atmosphere and you have no longer got a closed fuel tank and evaporative unit, so fuel system rust is likely.. 
  • The balloon would inflate to be larger than the test station. 

Run the car off the starter motor with batteries and sound system playing engine noises up to 2500rpm? 


However, to burst your Brexit and environmental bubble

7 hours ago, cavedweller said:

idiotic, incorrect and pointless emissions regulations … foisted upon us by the drunken unelected fools of the EU

here is some expert evidence 







“30.We want vehicle manufacturers to show that they can be part of the solution as well as the problem. The UK led the way in Europe in pushing for tough new type approval standards for cars and vans, including the ‘real world’ driving emissions tests that start to take effect from September this year, alongside tougher laboratory tests. We want to be absolutely sure that these new standards will deliver, and that we see a significant reduction in harmful emissions from new models of cars and vans.”


See rule 31 of the 0.2% of 4000+ EU rules the UK has been defeated on. 




European elections will  probably take place on the 23rd May. 

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Wow. That "DVSA  In Service Exhaust Emissions" thing is a longwinded waffle! I haven't read the whole thing yet (and probably won't) but unfortunately it sort of already begins to fall apart from the very beginning where it says in part 1.3 Test Procedure that " the tester will assess the smoke emitted from the tailpipe...", which basically means it still relies on the judgment of the person doing the testing to determine if the vapors coming out of the tail pipe are the wrong colour or scent. That's not very accurate or scientific, and probably not fair either. Lots of scope for error and just plain bad practice.


I've always been critical  of the MOT where it leaves anything to the discretion of the tester. It seemed to be an especially dodgy time in London in the 1990's. I've had bikes fail the MOT simply because the tester was in a bad mood and decided to use "discretion" an excuse. I even had a bike failed on rear wheel bearings (something you can't see and can only minimally assess under the circumstances) and the wheel bearings in question were less than a day old and got fully passed 20 minutes later by a more reputable tester at a different MOT station. The "discretion" part of the MOT just means that an MOT tester with an agenda, a bad attitude or just plain incompetence can fail a vehicle simply because they want to, and there's little use in filing any complaints because they just get ignored. It's been my experience that the whole MOT fiasco in the UK has always been a dodgy mess at best so in modern times giving any reason for failure over to the discretion of the tester seems totally unprofessional and unnecessarily chancy for the poor sod who owns the vehicle in question.


As far as the whole pollution question goes, there's no way my 20 year old 999cc car is worse for the environment than the string of newly manufactured Range Rover clones so many people buy on a regular basis nowadays. My car was made a couple of decades ago and no new manufacturing or transporting pollutants have come of it since then apart from the wheezy little exhaust of it's 999cc engine. You will never convince me that 20 years of this pathetic little Polo trundling the roads at 50mpg is a worse thing than buying a new monster car every couple of years that's MOT exempt and driven like a lunatic. I mean, have you SEEN what passes for a Mini or a Fiat 500 nowadays? And they're considered SMALL! Dear God, what have we come to when we're all encouraged to buy a fancy-pants, newly manufactured contraption with a six liter PETROL engine every couple of years in order to "save the planet"?


I'd gladly have an electric engine my 2000 Polo, but I bet there's no way I could get away with it legally building it myself and at the moment it's a frightfully expensive thing to convert a car to be electric so little people like me who won't or can't buy a brand new MOT exempt vehicle every year still have to use dinky little old secondhand petrol engines, and anyway I doubt my 2000 Polo is the cause of very many penguin deaths. And what have those penguins ever done for ME anyway? Bloody foreign layabouts...



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has a complaint process. No idea whether it is effective.

I got failed for weld repairs underfloor one time, completed the previous year to pass MOT at another garage with no corrosion since.

Checked with the tester who admitted he was not a welder and the repair was structurally intact but ugly. 

He also did not know about old Polo dangly shocks. Told car mates like the Fendubbers crew. Never went there again. Site is now just a car wash.

Covered the "ugly" seam with underseal, which had been removed in the prep work for a clean join mostly from above.


Absolutely, the pollution cost of manufacture and disposal can match lifetime emissions of well maintained car.


That's what I keep telling myself.


720 grams of CO2 per £1 of new purchase cost. Even for electric vehicle using Lithium and Cobalt.

I agree, lighter and simpler and efficiently made is less impact I imagine.


If your Polo was born in 2000 and hasn't celebrated its birthday yet is it not really an 18 year old car or a 19 year old car?

Never mind. It's only maths, I'm going to try some rounding up too.


So 31.7 million cars in use in the United Kingdom in 2016 divided by 36,000 projected deaths due to air pollution is 880 cars per death.

People not penguins. But not enough to reduce the impact of people, that needs more extreme heatwaves, droughts, storms and deeper and longer floods

which is the tipping point consequence - about 11 years away I hear.


To simplify my working I'll momentarily neglect the manufacturing emissions which have happened and

assume nitrogen dioxide to carbon dioxide ratio is similar for all cars, then

let's say a year 2000 1 litre Polo at 50mpg is 131 grams per kilometre CO2 and a RangeRover 2 litre is 72 g/km


then the single Polo is causing 1.8 times more death than the single RangeRover 2 litre.

But a RangeRover 4.4 litre V8 is 389 g/km causes 2.9 times more death than the Polo.


There are about 5500 v8 RangeRovers registered (I'm including SORNed bear with me)


splitting over the 880 cars per death is 6.2 deaths. (Feynman joked that babies come in lumps so must be counted in whole numbers).

Times by 2.9 for the worse than a Polo factor = 18 deaths due to v8 RangeRovers.

Times by 6 for manufacturing emissions versus the Polo is 108 deaths in one year due to those 5500 v8 RangeRovers.

(assuming all countries use the same Earth atmosphere - a difficult concept for some climate change deniers).


Only 35,892 deaths to attribute to other car types and models and engine sizes including "RangeRover clones".

Need a clue here. What 6 litre petrol? 


Seen the Landwind X7 ? It's got a 2 litre Mitsubishi turbo petrol engine.



Vw Polos outnumber RangeRovers but trying to work out how many from the open data here killed a LibreOffice Excel clone



For the moment using the 880 joint death liability number I'll assume my ancient Polo (or yours) causes

0.0006 to 0.0011 deaths per year due to air quality pollution currently - the lower bound of those two values allowing for amortised manufacturing emissions.



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I hit a pheasant the other day, does that, by mathematical derivation cover the deaths my car will cause for the next 1000 years? 


In which case, can I get cheaper road tax? 

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Good question.

I am also at the 1 death per thousand years forecast calculation for people by pollution but not by impact.


Yeah, suicidal pheasants throwing themselves under approaching cars, know exactly that experience. It's worse when they travel in pairs

or a family. Proper DeathRace2000 scenario. 


Clearly unrelated because from experience, for animal deaths by impact its about 1 every 7 years for me - a pigeon (took out a wing mirror), a pheasant, a rabbit, a cat

(ran under the low car - saw it in rear view mirror not running straight, went and found the poor injured thing and carried it, with help from a neighbour, dead, to the owning family who had recently moved to the busy road).

And I keep seeing dead badgers at side of road.


Does not reduce probability that you will hit a person or pet or deer in future if the event is beyond your control.

Insurance might go up - any excuse to say you are a higher risk. 


Where are all the insects?

Used to splat hundreds on the windscreen.

There's no change in  car aerodynamics (only had the front air dam for a few years) . Can see them in the garden so it's not too cold or early..


Doubt you'll get road or fuel tax discount. Hearty meal for someone or carrion birds that can no longer be shot.


Some shoot owner will charge you for depriving them. 

Though your neck of the world I imagine it was wild not released, which creates artificially more birds than the environment can support making it okay to shoot them.




… but my moral quandary with that statistical forecast calculation is this.


Are there 999 other drivers like me making it a human death every year?

That death could be my grandchild.


That means I do need to keep emissions under control and regulations and tests are not pointless or incorrect.

Edited by dvderlm
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Badgerland thinks 52% killed in road accident, but yeah, they never look like something smashed into them at 60mph. 



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Unless it was the farmer, in the field. Always laying nice and neat in the gutter


They are a big problem in farming so not gonna hate on them for it

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But Cambridgeshire doesn't have dairy farms with cattle, it's salad, rapeseed, carrots, wheat and sugar beet.



Badger baiting collateral damage?



There are poultry farms though and fruit trees (no fruit on them now). I suppose farm tracks could be undermined, but why not just bury the carcass in a field if you are a farmer

who killed a badger illegally..


Edited by dvderlm
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