Development of Mercedes’ new in-line six-cylinder engines is well underway, Autocar has learned.

Long regarded as a defining characteristic of the brand, its straight sixes were phased out in the mid-1990s.

The engines are part of a new modular powertrain architecture that will spawn three and four-cylinder units as well as the six-pot versions. The new engines are expected to be launched in 2016 under the bonnet of the next-gen E-class, codenamed W213.

The forthcoming C-class is likely to receive the new engine family in 2017 as part of a mid-life makeover. The engine line-up will include the new three-cylinder unit that is said to boast enough refinement to satisfy Mercedes customers.

What’s being dubbed ‘Autobahn Pilot’ is also likely to arrive in 2016 on the E-class and in 2017 on the C-class. Company insiders say the system is an “autonomous driving assistant with an overtaking function”.

For the short term, sources have now confirmed that the new C-class AMG model will get a twin-turbocharged 4.0-litre V8 engine. It will drive a seven-ratio Speedshift automatic transmission and have the option of all-wheel drive. A nine-speed Speedshift is also under development and is expected to appear during the 2017 mid-life refresh.

Development work on the C-class plug-in hybrid is in its final stages, too, with Mercedes hoping to achieve a CO2 rating of 60g/km when the vehicle’s certification process is completed.