A consumer organisation has turned the heat up on turbocharged engines, claiming they don't deliver on economy claims.

The study on small turbocharged engines claims the are making fuel economy promises they can't keep.

Consumer Reports examined 27 cars and found that small-capacity turbo engines used by Ford and General Motors were inferior to conventional cars.

They found the Mazda3's non-turbo engine accelerated faster and had better fuel economy than the turbocharged Chevrolet Cruze, which is also assembled and sold in Australia by Holden.

The soon-to-be-discontinued Toyota RAV4 V6 matched its claimed fuel figures while offering competitive fuel economy and superior performance to the turbocharged Kia Sportage and Ford Escape.

US fuel economy figures were under the spotlight before the Consumer Reports test, with some Ford drivers claiming their cars did not meet mileage claims made by the blue oval.

The Environmental Protection Agency is investigating claims that Ford overstated hybrid fuel use by as much as 1.3 L/100km.

Ford is not alone - the EPA criticised Hyundai and Kia last year after the brands' economy claims were found to be inaccurate.

The most inaccurate fuel figures were attached to Kia's Eco models.

Kia and Hyundai say they will reimburse almost 1 million customers for the cost disparity between their fuel figures and real-world use.

The disparity between claimed fuel economy and real-world figures is a common complaint among motorists, who often struggle to match what governments or manufacturers say cars can do.

Australian fuel figures are obtained in a laboratory that mimics the demands of city and country driving. Cars are subjected to the same test, and many will use more fuel than the government sticker suggests.

The UK-based Honest John motoring website invites drivers to compare real-world fuel economy figures with manufacturer and government claims.

More than 30,000 cars have been listed there, with drivers on average reaching 87 per cent of the official fuel figure for their model.

The Toyota MR2, Land Rover Defender and Jaguar S-Type are listed among the cars with the most realistic fuel claims, while Peugeot, Renault and Volkswagen are listed as having the most realistic figures. Audi, BMW and Mercedes drivers found it tough to match their car's fuel figures.

--Drive.com

- Sydney Morning Herald

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