RAC Cars News


New Report Slams Smaller Engines

By raccars Published

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Apparently, the idea that larger engines are greedier than smaller versions could be a myth, according to a report by data analysing firm, Emissions Analytics. Discrepancies in the testing methods used to compile official mpg data could have given big cars, such as 4x4s, an unjustly bad reputation.

Five hundred cars, half each of petrol and diesel, were tested by driving for three hours on public roads in Britain, resulting in an mpg figure 18% lower than manufacturers' official figures. Emissions Analytics believes that the real world testing situation reflects a more realistic use of fuel by accelerating harder and travelling faster, as opposed to the laboratory conditions used by manufacturers. The difference in the amount of fuel used between the two different tests was more marked for smaller cars, as these are exercised harder by the extra acceleration.

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Vehicles with engines of one litre or below came with official manufacturer mpg figures averaging 60.3mpg, but, in real world testing conditions, returned an average 38.6mpg - 36% lower. However, vehicles with engines between one and two litres in size posted official mpg data of 59.1mpg average but managed 46.7mpg in real world, only 21% below manufacturers figures. In effect, this meant the larger engines accomplished higher mileage than smaller cars for the same amount of fuel. The trend continues as engine sizes increase, with cars in the two to three litre size engine bracket testing at 45mpg, only 15% lower than their official average of 52.9mpg.

Fuel economy was worse for high performance engines but real world testing produced results closer to the official figures given by manufacturers.

Overall, one to three litre engines proved to be the most economical in real world testing with results of 45-46mpg on average. Buying cars with two to three litre engines, only 15% less efficient than advertised, could be less disappointing than smaller engines that produce far lower mileage than expected.

The laboratory testing process used by manufacturers to measure mpg data is regularly criticised by motoring organisations for failing to reflect the rate of acceleration and higher speeds used when driving on public roads. Emissions Analytics believes this is encouraging consumers to buy certain vehicles, believing they are more economical and environmentally friendly than they actually are. With some two million new cars sold annually in the UK, small cars are the most popular class - largely because they are supposed to be more efficient.

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