taxi's blowing black smoke - whats that all about

ScottDougall

I have noticed a few times now that some taxi drivers - after they overtake you and if the might feel agreaved at you having been in their way that these taxi drivers have what seems like a new trick

I think they shift up a gear then rev then deliberately labour the engine producing thick black smoke from their exhaust...

now if you accept that they are doing this and that its something that is catching - then you can begin to imagine then talking together cant you - telling each other about this new trick and how to do it, how many time they have done it...

its a bit like the miss adjusted windscreen squirter thing - that also takes a bit of setting up and forethought

makes you feel a bit sad for them doesnt it - that they should try so hard to behave like a child...

has any one else come across the "taxi smoke screen" meme then - I would be interested to know !!

nwallace

Taxi's make me wonder, I struggle to believe they meet the Euro requirements for Diesel engines, put a modern saloon/hatch based taxi up next to the latest a London Taxi Co. TX4 or what ever is the latest, watch the exhaust and listen to the engine.

b0y1nterupted

they do it to warm your legs on cold mornings

counterculture

a taxi cut me off and done this smoke trick, i flipped him the bird, he slowed up, tried to box me in behind a parked car while shouting abuse through the window, only for a police car to pull out from a road behind me, and see the whole thing, minus me flipping the bird, pulled the taxi over and left me to get on my way. F*** em!!

the_hundredth_idiot

nwallace wrote:

Taxi's make me wonder, I struggle to believe they meet the Euro requirements for Diesel engines, put a modern saloon/hatch based taxi up next to the latest a London Taxi Co. TX4 or what ever is the latest, watch the exhaust and listen to the engine.

The latest TX4 has a 2.5 litre diesel engine which emits 233 g/km of CO2* yet produces only 75kW (which is about 100 bhp - i.e. about the same as a new 1.4 litre Ford Fiesta which emits 154 g/km). And that's the new, more "efficient" one - god knows what the older ones are like. :shock:

http://www.lti.co.uk/tx4/technical-specification/
http://www.config.ford.co.uk/fordconnec ... uelspc.htm

But black cabs are exempt from the congestion charge and encouraged to drive around London all day, creating both pollution and congestion. If you understand the rationale for that, you have a more warped and twisted mind than me. :evil:

(* That's for the automatic; the manual is only 211 g/km but I'm fairly sure virtually all black cabs are automatic - I know I'd get an automatic if I was driving around London all day.)

peach1

In Belfast we have the "smokey car hotline" - it's on speed dial on my mobile and they seem to always follow up the calls. I'm sure it causes enough aggravation to the driver - you're bound to have something similar.

soy_sauce

it not just the taxi, i got it from another drivers too.... well, don't know if they did it intentionally or not tho... :? thinking about getting one of those pollution mask, does anyone use them and are they any good?

biondino

They're useless, basically, and uncomfortable in my experience. Oddly I found the pollution annoyed me much more when I was riding a moped than a bike.

RyanB

In Belfast we have the "smokey car hotline" - it's on speed dial on my mobile and they seem to always follow up the calls

We have? ?

Whats the number? Theres a few people I'd love to report!

DavidTQ

The Hundredth Idiot wrote:

nwallace wrote:

Taxi's make me wonder, I struggle to believe they meet the Euro requirements for Diesel engines, put a modern saloon/hatch based taxi up next to the latest a London Taxi Co. TX4 or what ever is the latest, watch the exhaust and listen to the engine.

The latest TX4 has a 2.5 litre diesel engine which emits 233 g/km of CO2* yet produces only 75kW (which is about 100 bhp - i.e. about the same as a new 1.4 litre Ford Fiesta which emits 154 g/km). And that's the new, more "efficient" one - god knows what the older ones are like. :shock:

http://www.lti.co.uk/tx4/technical-specification/
http://www.config.ford.co.uk/fordconnec ... uelspc.htm

Apologies in advance for the car techy bit here. Im a barely reformed Rally Driver, Car based maths was a big part of the hobby.

BHP figures can give a very "Skewed" picture of engine power \ performance.

BHP calculation figures are caluclated by multiplying by the revs the torque the engine is delivering. Literally you take the torque of an engine in imperial ft/lbs multiply it by the revs then divide by 5252 and thats the horse power at a given revs. It doesnt take a genius to see that you can inflate the Bhp figure of an engine by simply taking where it makes its maximum ft/lbs of torque and moving it up the rev range. That is why BHP figures are virtually meaningless "pub talk". People love quoteing them, but they dont really mean a lot without a power graph and "real" torque figures

Basically two engines can have the same ft/lb (or nm) of pulling power but if one made it at 2000 revs and one at 6000 revs the 6000 revs car would have a FAR higher Bhp figure even though its actually no more "able" or "powerfull" it just has to spin more to get there.

Take a look at a power figure which doesnt get skewed into meaninglessness by rev range, the actual torque produced by the black cab is 240nm at just 1800 rpm that 1400 fiesta manages to turn out 125nm but because its put it out at a far higher rev range it "inflates" the BHP figure. IF the black cabs maximum torque were moved from its 1800rpm up to 6000 rpm (without actually changeing the engines real power at all) it would gain a somewhat more respectable 202hp at 6000rpm and have to be rev'd to heck to get there, however that wouldnt be the BHP figure in the brochure, because they would look further along the graph to see how far they could push the figure, because although peak torque might have been reached at 6000rpm the rev part of the calculation carries on going up so if this same engine carried on to produce 200 nm at 8000rpm (and this was the peak of the BHP calculated curve) this gives a figure of 223hp. Even though by 8000rpm it was producing less "power" than it was at 6000 rpm because the revs are higher the calculated (and thats all it is) figure is higher.

This is also the reason why BHP figures for cars seem to have been rising over the years as cars have moved to 16 valve engines, modern 16valve engines barely do anything until they get to 4000rpm, if you keep a 16 valve engine under 3000 rpm you'd hardly have any power at all. Because the'yre maximum torque is so high up the rev range they get higher BHP figures. All it actually means is that they are having to spin faster to get to it.

Purely off the top of my head but could this moving of the power band up the rev range be a part of the cause of the rise in driver impatience? Drivers feel they "have" to put their foot down in order to make progress because their engines feel gutless at low revs?

The taxi's engine is far better suited to driving in busy traffic smoothly and reliably. It makes all its torque way down the rev range meaning it can pull away and make progress without having to rev the living daylights out of it. This also has the benefits of lowering mechanical wear and tear on the engine. The London taxi has to haul around nearly 2 tons of metal. The engine no doubt sacrifices some efficiency to the altar of reliability \ over engineering, But the comparison of co2 vs bhp out was not a fair one.

Apologies again for the techy post, Rallying is a FAR more Geeky hobby than youd think especially for the privateers who have to build their own cars.

I remember doubting an old engine builder when he first told me that hp figures were "bull" as they were all I had heard about when talking about "fast" cars. But the guy had a hell of a reputation so we used him. I still remember being very dissapointed with the rolling road BHP figures on that first engine although not at all dissapointed with the way it drove, it all changed when I drove a few more cars with the same base engine and 30% more bhp on paper but FAR less power on the track Later I got more into the maths and came to understand far more about how it all works.

also of importance to a cars "performance" is the spread of the power, how big a rev range is covered by high torque output. But this post is long enough as it is...

Here ends the geeky car post...

peach1

RyanB wrote:

In Belfast we have the "smokey car hotline" - it's on speed dial on my mobile and they seem to always follow up the calls

We have? ?

Whats the number? Theres a few people I'd love to report!

90270420

Roastie

DavidTQ wrote:

Apologies in advance for the car techy bit here. Im a barely reformed Rally Driver, Car based maths was a big part of the hobby.

a) Thanks for saving me for revealing my car anorak tendencies.
b) Don't feel alone, I have more tools in my toolbox for fettling my race and rally cars than bicycles - tho' I am working onredressing this balance.

the_hundredth_idiot

Cheers, DavidTQ - I think I followed most of that.

I did unfairly pick the Fiesta for comparison on bhp terms, I'll accept that. And, even without the techie argument around power output, London taxis are clearly designed to be durable rather than fast.

But, my main point was around the amount of CO2 these London taxis pump out. If (accepting that it's an if) cars which produce large amounts of CO2 emissions are a bad thing (look at the VED high emissions cars have to pay and the proposals for the Congestion Charge) then why are London taxis seens as a good thing (exempt from CC) when they produce such high levels of CO2 emissions?

And London taxis don't feel particularly powerful - I used to live in north London and some of the older taxis really struggled to make it up Archway Road.

DavidTQ

The Hundredth Idiot wrote:

Cheers, DavidTQ - I think I followed most of that.

I did unfairly pick the Fiesta for comparison on bhp terms, I'll accept that. And, even without the techie argument around power output, London taxis are clearly designed to be durable rather than fast.

But, my main point was around the amount of CO2 these London taxis pump out. If (accepting that it's an if) cars which produce large amounts of CO2 emissions are a bad thing (look at the VED high emissions cars have to pay and the proposals for the Congestion Charge) then why are London taxis seens as a good thing (exempt from CC) when they produce such high levels of CO2 emissions?

And London taxis don't feel particularly powerful - I used to live in north London and some of the older taxis really struggled to make it up Archway Road.

Some of the "older" taxis are running the perkins diesel which I believe have some antiquated origins.

I have to say though that on the "green" front I dont see as taxis are any more "green" than a private car. Any gains made by the engine being kept "warm" (diesel engines can actually be less efficient on short journeys than their petrol equivalents) will be negated by extra journeys to pick up point and from drop off point. That said I dont often use taxi's either so cant claim to be an expert on all aspects of the taxi trade. Their may be a hidden factor that isnt immedeatly apparant to me.

I would guess (and I dont live in London and have never paid the congestion charge so I wouldnt know)the main reason for taxi exemption would be on a job protection basis, although surely any courier \ delivery company would want similiar exemptions.