The Suzuki Swift will gain a new Dualjet 1.2-litre engine next year that is said to improve economy by 16% while also reducing CO2 emissions below the magic 100 g/km, making the Swift free of road tax.
The Dualjet technology uses twin fuel injectors that can be positioned closer to the inlet valves, and this allows for improved fuel atomisation and more efficient combustion.
Further modifications have been made to improve gas flow, reduce frictional losses, and increase the compression ratio from 11:1 to 12:1.
In official tests the result has been an improvement in fuel economy of 9.2mpg on the combined cycle, to 65.7mpg, while emissions fall to 99 g/km.
Maximum power falls slightly from 94PS to 90PS, although torque increases from 118Nm at 4,800rpm to 120Nm at 4,400rpm.
A stop/start system has also been added for the first time, while the gear ratios have been revised.
The new engine will initially be available on SZ4 two wheel-drive models as a cost option, expected to be around £500.
The Dualjet technology is expected to be available in early 2015.