cuprajake

iTrader: (11)

Be interesting to see the percentage in fuel price increase.

Re tax.

A customer has a dodge viper srt 10 truck. 8.0 litre and a corvette 6.2l both are under £250 a yr tax. !

f1_fan

iTrader: (9)

You sold your worsening image? Well your current one ain't too good either.

stevebt

iTrader: (8)

Only fair due to what he will be paying the fuel them Gotta love the Dodge truck

chocolate_o_brian

iTrader: (22)

Cheaper to chop it out and tweak the map isn't it?

A work mate just did it on his 07 plate derv Golf.

AndyC_772

iTrader: (2)

Fuel economy and CO2 emissions are just two different ways to measure one and the same thing. They're inextricably linked; all the carbon atoms that come out of a vehicle's tailpipe originally entered the vehicle via the fuel filler.

The relationship between the two depends on the fuel, not the vehicle. If you burn X amount of petrol to travel a mile, then the amount of CO2 produced is simply the amount of CO2 which is (always) released when X amount of petrol is burned.

Have a look here - there's a chart at the bottom of the page which shows the relationship between mpg and CO2/km for petrol and diesel.

hodgy0_2

But Fuel economy has a concept of time/distance

co2 emissions do not, and are measured at a standstill

Matteeboy

I give you the M135i - most are getting low 20s to the gallon yet it's only 178g/km.

There is a rough link but there are definitely some cars good on mpg with poor CO2 emissions and vice versa.

AndyC_772

iTrader: (2)

Eh?

Fuel economy and CO2 emissions are both measures of quantity per unit distance. Time doesn't enter into the calculation.

There's quite a comprehensive discussion of the topic here - but the important thing to note is that the complete combustion of a litre of fuel produces a certain amount of CO2, so provided the car isn't chucking out significant amounts of CO and unburned hydrocarbons, mpg and g/km are just measures of the same thing.

They may, of course, be measured at different times and under different conditions for the purposes of tax and other non-scientific purposes, which will lead to a discrepancy - but that's just needlessly confusing.

hodgy0_2

co2 emissions tell you a lot about the efficiency of an engines combustion process, but not much about fuel economy

AndyC_772

iTrader: (2)

It tells you something about the *completeness* of combustion, ie. what proportion of the fuel that's burned ends up as carbon dioxide, but that's close to 100% in any modern engine. Unburned fuel results in CO and HC emissions which are oxidised by the catalytic converter, and levels are of course, very tightly limited by law.

That's not the same thing as efficiency, which is a measure of how much of the energy from the fuel is converted to useful mechanical work, as opposed to being lost as waste heat.

hodgy0_2

This is my point

I suppose you could be getting at this as well. Does the mpg rating of a car correspond to the amount of CO2 produced? The answer to that is maybe. the actual Liters / mile depends on multiple factors. Like driving conditions (hills for example), whether or not you're using your air conditioner, the quality of your air filter, etc. A car rated for 21 mpg may actually only get 15 mpg while a car rated for 17 mpg may get 22 mpg...

A fuel efficient engine, with the corresponding low co2 emissions will not give very good fuel economy if used to power an Abrams main battle tank

AndyC_772

iTrader: (2)

Sure, if you drive a vehicle under different conditions, it'll use a different amount of fuel to travel a given distance - but then it'll also emit a different amount of CO2.

You can't create or destroy carbon atoms. All the carbon that goes into the car through the fuel filler has to go somewhere, and that 'somewhere' is out the tail pipe.

BTW a small engine in a large vehicle does actually give good economy, because the throttle will be more open more of the time - and that's good for the thermodynamic efficiency of the engine. It's precisely why small engined cars tend to be more economical than large engined cars, despite the fact that at large engine has a greater ratio of volume to surface area in the cylinders, with correspondingly reduced heat loss.

hodgy0_2

i absolutly agree with that, but I suppsoe my point was the concept of fuel economy is not solely and "in / out" equation

and surely "time" has a part to play in the whole fuel economy discussion because without "getting anwhere" which is measured in feet/sec or miles per hour the fuel economy debate is pointless

out of interest the CO2 fugures that are quoted are they measured whilst the car is moving (or simulated on rollers) or are they just a simple equation based on "we put this much fuel in and this much comes out the back" with the engine running at a set rpm

markjmd

iTrader: (11)

They're measured using blatantly rigged and manipulated tests, with no sly little trick for gaining any small increase in fuel efficiency considered too dirty:

.... which all add up to a nearly 25% gap between manufacturer-quoted and real-world MPG figures for cars on sale now, compared with only around a 10% gap 15 years ago.

How they can get away with it, given the amount of EU rules and tax incentives there are now on fuel-economy standards for car manufacturers, is pretty astonishing.

dunx

iTrader: (3)

WOW do they really selectively only ingest the carbon free constituents of the air we breathe ?

LOL

dun