Many cars, including the Mazda CX-5 and Volkswagen Golf, use variable valve timing to maximize fuel efficiency and performance.

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Mr Groome was last seen driving a 2002-registered black Volkswagen Golf car, which police said had been customised and was distinctive.

BBC: Thomas Groome

GM's big German subsidiary, Adam Opel, is already indicating that it will offer discounts on its new Astra model, to be launched in April, which will compete head-on with Volkswagen's new Golf itself already being discounted.

ECONOMIST: Ford, Fiat and failure

Last year the company knocked Volkswagen and its Golf off the continent's small-car sales perch.

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The so-called DualTronic transmission technology debuted in 2003 in the Volkswagen Golf and Audi TT and is quickly gaining popularity in Europe.

FORBES: Magazine Article

Entries included a Chevrolet Volt, Nissan Leaf, Honda CR-Z, Honda Civic GX, Toyota Prius, Volkswagen Jetta TDI, a Volkswagen Golf TDI that runs on French Fry oil, and the Judy Sunhawk, a solar car capable of going 90 miles an hour.

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