Porsche was criticised for dropping the naturally aspirated flat-six engines in the Porsche Boxster and Cayman models for the turbocharged units in the new 718s. An awful lot of that criticism revolves around how the noise of the forced-induction four-pot kinda sucks, especially when compared with the wonderfully aural atmospheric units they replace. However, a new report by the British motoring magazine What Car? suggests the new turbo engines fall short on another level entirely.

As part of the magazine's True MPG test, What Car? discovered the 718 Cayman S is not quite as efficient as Porsche claims it to be. Though the tested 28.4 mpg versus the claimed 34.9 mpg doesn't sound too egregious at face value, things do start to go downhill for the Cayman when you discover it doesn't fare as well when compared with the other sports cars in the test. Despite being larger and heavier cars with bigger engines, the BMW M2 and Jaguar F-Type Coupe V6 managed to return 31.4 mpg and 28.8 mpg respectively. Worse still, the old 987-gen Cayman S with the 3.4-liter flat-six returned in What Car?'s True mpg 2014 test a noticeably superior 31.8 mpg economy figure.

Outside of the sports cars, the True MPG test culminated with some pretty interesting results. For instance, at 55.2 mpg, the Renault Kadjar SUV was 3.3 mpg more efficient in What Car?'s report than the Nissan Qashqai, even though both cars had the same 1.5-liter 110-hp diesel engine and are based on pretty much the exact same platform. Another interesting result when cross-examined with its peers was the Volkswagen Polo 1.0 BlueMotion. Not only was its True MPG of 51.1 a pretty big drop from the claimed 68.9, but the comparably sized Suzuki Baleno managed to beat the uber-efficient Polo with its 55.2 mpg result.