Benz heads back to the future

Only months before Australia's only locally-manufactured inline six-cylinder engine is killed by Ford, Mercedes-Benz has confirmed it will re-introduce I6s to its range beginning with the late-2017 update of flagship S-class saloon.

After years of media speculation, the existence of the six-cylinder petrol and diesel turbocharged engines and their on-sale timing were officially confirmed for the first time by Benz at a future drivetrain media briefing in Stuttgart this week.

Once the new I6s debut they will gradually replace the current V6s used across the Benz line-up, including AMG V6 biturbo models that are currently badged C 43.

motoring.com.au understands the importance of the new I6 will be signified by a new badge number designation never used by Benz previously.

The sixes will be close to 3.0-litres in capacity and are from the same modular family as new petrol and diesel 2.0-litre four-cylinder engines that will also spread through the Benz range.

The first of these fours, the OM 654 turbo-diesel, has been revealed and is being rolled out in the new E 220 d sedan that goes on-sale in Australia in July.

The various iterations of the engine family will all be turbocharged. The I6s will be used in combination with new 48-volt battery systems and integrated starter generator systems that will also debut with the S-class.

An ongoing wave of I6 plug-in hybrids will start with the S 500e update, which will also debut Benz’s inductive charging system and feature a new li-ion battery and operating system that will allow a 50km-plus electric range, up from 30km maximum today.

The S-class update will also start the widespread roll-out of particulate filters in petrol engines. Diesel particulate filters are already in universal use.

This is a 'back to the future' move for Benz, which relied on straight sixes – and a diesel five-cylinder – and fours as a mainstay powertrain until moving to V6s from 1997. Arch-rival BMW has stuck with I6s throughout this era.

Jaguar is another luxury manufacturer moving from V6 to I6 engine configuration over the next few years.

Meanwhile, Australia's own inline six, the Barra 4.0-litre ends production in October when Ford closes its local manufacturing facilities, killing it and the models it powers, the Falcon sedan and ute and Territory SUV.

While the Ford I6 is a global orphan and economically unsustainable, Benz is shifting back from V6s because the I6 offers production efficiencies in era of engine downsizing, allowing it to build four and six-cylinder petrol and diesel engines with identical bore spacing on the same production line.

"In the past six-cylinder was the standard for Mercedes and it made a lot of sense to combine V6 and V8 engines so we could make use of those combination benefits," Mercedes-Benz powertrain vice-president Bernhard Heil told motoring.com.au in Stuttgart.

"Nowadays the situation is changing a little bit. Eight-cylinder volume is more or less stable, six-cylinder volume is more or less stable and there is an increase in four-cylinder and we say now it makes sense to combine four and six cylinders."

But even more importantly, Heil revealed, was the advantage the I6 layout provided in terms of meeting ever-more stringent emissions levels while maintain and improving performance.

The move from natural aspiration to turbocharging over recent years means engines no longer have to be canted to allow long exhaust manifolds that produce better torque characteristics.

In that situation an I6 works better than a V6 because the turbocharger and emissions controls can all be fitted on the exhaust side of the cylinder head.

"A V6 has a 60 or 90-degree bank angle and has limited space at the exhaust if you would have to install turbocharged and after-treatment systems," Heil explained.

"I would estimate there is no chance to package that or if you would have the turbochargers in the vee like some modern engines you have no chance to add after-treatment systems in the vee.

"So we said let's think about an engine family inline with a lot of space on the hot side to install after-treatment."

Heil confirmed that development of the new inline family began five years ago. The various iterations of the engine family will all be turbocharged, will be used in combination with new 48-volt battery systems and integrated starter generator systems that will also debut with the S-class and an ongoing wave of plug-in hybrids, also starting with the S-class.

An ongoing wave of I6 plug-in hybrids, also start with the S 500e update, which will also debut Benz’s inductive charging system and feature a new li-ion battery and operating system that will allow a 50km-plus electric range, up from 30km maximum today.

The S-class update will also start the widespread roll-out of particulate filters in petrol engines. Diesel particulate filters are already in universal use.

It was also confirmed in Stuttgart that the new engine family will not be cut down to become a triple cylinder engine because Benz has instead opted to stick with small-capacity four-cylinder engines shared with technology partner Nissan-Renault.

Benz claims that when fitted in a comparable vehicle the OM 654 consumes around 13 per cent less fuel than its predecessor.

Benz cites optimised airflow on the intake and exhaust sides, the use of fourth-generation common-rail injection with pressures up to 2050 bar and a reduction in internal friction by around 25 per cent as an aid to fuel saving.