European automakers have been downsizing their engines for the best part of a decade, all in a bid to meet increasingly stringent emissions standards. But now, thanks to new, upcoming emissions testing slated to be more realistic, that trend may well be reversed.

Yes, according to a Reuters report, which cites "industry sources", a shift to engine "upsizing" is just around the corner.

These sources claim that Renault, General Motors and Volkswagen are all preparing to scrap many of their popular small, turbocharged engines over the next three years. Reuters adds that other manufacturers "are expected to follow".

Why? Well, in 2017 in Europe, all new vehicles are expected to have to undergo real-world, on-road (rather than in a laboratory) testing for nitrogen oxides. Similar realistic fuel consumption and CO2 testing is set to follow around two years later. And the downsized, forced induction engines – which have been set up to ace these official lab tests – are expected to struggle in the new on-the-road tests.

"The techniques we've used to reduce engine capacities will no longer allow us to meet emissions standards," Alain Raposo, head of powertrain at the Renault-Nissan alliance, told Reuters.

"We're reaching the limits of downsizing," he admitted.

Pavan Potluri, an analyst with IHS Automotive, explained that downsized, forced induction engines are neither as clean nor as efficient in the real world as manufacturers claim, largely due to the fact that they are typically driven at higher loads (than relatively larger engines) in the real world.

"They might be doing okay in the current European test cycle, but in the real world they are not performing. So there's actually a bit of 'upsizing' going on, particularly in diesel," Potluri told Reuters.

Thomas Weber, head of research and development at Mercedes-Benz, said this was the reason the German brand’s smallest engines were still comparatively large, with at least four cylinders.

"It becomes apparent that a small engine is not an advantage. That's why we didn't jump on the three-cylinder engine trend," he told Reuters.