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Mercedes-AMG's M178 Engine Versus Audi's 4.0 TFSI Plus

When the first reports about the latest AMG engine began pouring in, the V8 inevitably started being used in the same sentence with what Audi has achieved on their 4.0 TFSI.
Audi 4.0 TFSI Plus vs Mercedes-Benz AMG M178 1 photo
Photo: Image Edited by autoevolution
We say this because both engines are performance four-liter V8s with twin-turbochargers situated inside the cylinder lines, and now that the M178 has had its specs revealed we have found out that they are actually highly comparable.

Sure, the BMW N63/S63 engines - which were actually the first to use the so-called “hot inner vee” strategy for the positioning of the turbochargers – would probably also make for good candidates in a head on comparison, but both their cylinder displacement and power output aren't in the same league as the 4.0 TFSI from Audi and the new M178 from AMG.

In fact, with 510 hp and 650 Nm (479 lb ft) of torque, the M178 is pretty much neck and neck with the 4.0 TFSI Plus engine from the Audi S8 when it comes to their specific power output, with the Audi engine developing identical torque figures and 10 more horsepower.

In other words, the similarities between the two consist of engine architecture, cylinder displacement, power output and the positioning of the twin-turbochargers inside the cylinder lines. This is where the similarities end though, because when it comes other details AMG has done things a bit differently.

While Audi is ahead when it comes to their active cylinder-on-demand (COD) technology or twin-scroll turbochargers for better engine response, Mercedes-AMG actually went with a pair of Borg-Warner-sourced single-scroll turbochargers, while all eight cylinders are being fired up all the time. For this reason, the AMG mill may also offer a better natural sound, without the addition of articially-induced noises in the exhaust or the interior like some BMW and Audi models.

On the other hand, the AMG M178 uses a dry-sump lubrication system and a rather low charging pressure from the turbochargers, with only 1.2 bar (17.4 psi) of pressure being injected into the intakes.

For this reason, we think that while Audi's engine is not that far from its maximum output, with the RS6's 560 hp and 700 Nm (516 lb ft) of torque being close to what it can be safely extracted from it, the AMG lump is just at the beginning of its development.

Not only that, but thanks mainly to the dry-sump lubrication system, the M178 engine weighs only 209 kg (461 pounds) and sits much lower in the engine bay compared to the less compact 4.0 TFSI Plus, which weighs 224 kg (494 pounds).

All in all, we can't get an all-out winner until some fuel economy and performance figures on comparable vehicles are released, but the new AMG mill is a pretty good first try in this segment. Which of the two do you like more at this hour?
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About the author: Alex Oagana
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Alex handled his first real steering wheel at the age of five (on a field) and started practicing "Scandinavian Flicks" at 14 (on non-public gravel roads). Following his time at the University of Journalism, he landed his first real job at the local franchise of Top Gear magazine a few years before Mircea (Panait). Not long after, Alex entered the New Media realm with the autoevolution.com project.
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