The trend of making engines smaller is over, says Herbert Diess, Volkswagen's chairman, marking an end to a decade-long development where engine capacity has been reducing leading to the current vogue for 1.0-litre, three-cylinder engines.
"The trend of downsizing is over," he said at the launch of the new updated version of the Golf – VW's most popular car.
"Emissions tend to go up as engines get smaller," he said, referring to the way that small-capacity engines can perform worse in real world Driving Emissions Tests (RDE) due to be introduced in Europe in 2019 as part of the Worldwide Harmonized Light-duty Vehicles Testing Procedure (WLTP).
Diess says VW will continue with its current 1.0-litre, three-cylinder engine for its smaller cars such as the Up and Polo, but it will not be developing smaller petrol engines than that and its diesel units will not be getting smaller than that current 1.6-litre unit, either.
"Small diesels are just not economic," he says. "The Polo is currently 30 per cent diesel, but as diesel gets more expensive [to meet RDE tests], it will not be as popular."
He says the popularity of diesel engines, which in some European countries take more than 50 per cent of the market, "has not been a customer choice, but a result of favourable tax regimes. Once you have a price advantage, people will play along", he says.
So while the next generation Polo, due this year, will be offered with a diesel engine, Diess isn't as sure that its replacement will have an oil-burning option.
"It is difficult to predict," he says. "Today diesel take-up is still strong, but if you look at the difference between the current [economy] cycle and RDE it is worse in Germany, where the test only requires between nine and 10 kilowatts [12 to 13bhp] to do, but on the autobahn you need 100kW [124bhp]to do 200kmh [125mph]."
He says the disparity between current tests and real-world consumption and emissions is also wide in China where cars sit in traffic for much of their lives, but the new American tests, which have effectively added 40 per cent to the total emissions detected in tests, have closed the gap.
His opinion echoes a Reuters report last autumn which stated that new emissions tests had exposed flaws in downsized engines. In real life, the report stated, these turbocharged units have a tendency to overheat when their tiny turbos are called on to deliver real-world performance.
To combat this, the engine's software strategy will over-fuel the engine, which results in increased emissions of CO2, oxides of nitrogen as well as unburnt hydrocarbons, particulates and carbon monoxide.