Car makers such as Volkswagen, Renault and Vauxhall will slow the development of downsized engines and bring back larger capacity units following the introduction of new emissions tests, according to reports on Reuters.
Reuters says that the implementation of new real-world testing procedures has exposed flaws in downsized engines, which were predominantly developed to achieve low emission ratings in older laboratory tests.
New real-world data has shown that downsized units can sometimes perform worse than larger ones for CO2 and NOx output, largely because of the heat generated by their turbos, which they depend on more to develop power.
While lab tests were unable to reveal these downfalls, new real-world testing, which will come into force by 2019, shows it more clearly.
Common issues in smaller units include overheating that requires over fuelling to keep engine temperatures cool. This, in turn, results in more unburned hydrocarbons, particulates and carbon monoxide.