In the Mercedes-AMG GLE 53 Coupe we’ve been testing is a revolutionary new engine from Mercedes-Benz. It’s big news not only because it marks the return of the silky refinement of an inline six-cylinder engine, but because of all of its firsts in technology.

The 3.0-liter inline six is turbocharged with an output of 429 horsepower and 384 pound-feet of torque. It has a milder variation available for other models at 362 horsepower and 369 pound-feet of torque.

Remarkable is the first use of a dedicated 48-volt integrated starter alternator (ISG) at the rear of the engine that provides power for previously belt driven accessories such as the AC compressor and water pump. These components remain bolted to the engine but a drive belt is a thing of the past.

Called EQ Boost, this a technically a mild-hybrid system. In such the ISG can provide an additional boost of 21 horsepower and 148 pound-feet of torque on demand for extra acceleration, for maintaining vehicle speed in coast conditions, and providing the smoothest idle-start-stop experience I have ever experienced. Starting up from and a resting idle at a stoplight for instance is nearly imperceptible.

The ISG can also capture power through mild regenerative braking to charge back its 48-volt battery. While the 48-volt system powers all of these engine related components, a 12-volt subsystem remains to power to systems such as lighting, interior, instrumentation, infotainment and computer controls.

To performance, the powerful ISG provides voltage to its also first in production Borg Warner electric auxiliary compressor (eZV) which spinning up to 70,000 rpm in 300 milliseconds can provide intake boost the engine needs at start up when the traditional turbocharger is still waking up – eliminating turbo lag entirely. This further enhances the engine’s ability to get with the program when idle-start-stop is in action.

Looking to the intake hardware, ambient air is drawn through a long snorkel from behind the grill around the rear of the engine to the throttle body mounted directly onto its sizable turbocharger. Air from the compressor then travels through two separate tracts, one to the ezV where it can be given an extra immediate dose of boost, the other directly to the engine.

Regardless of which boosted air source, the intake charge then flows through an air to water inter-cooler integrated into the intake manifold for packaging and thermal efficiency. This allows the heat exchanger radiator to be more easily placed, in our GLE is located down low behind the left side fascia.

Chain driven dual overhead camshafts can operate with both variable valve timing and variable valve lift utilizing a multi-lobe camshaft which can be slid back and forth laterally with electronically controlled actuators. Direct fuel-injection with Piezo injectors fire each of the engine’s 500cc combustion chambers.

Further taking advantage of its compact packaging ethic, the catalyst components are moved up to immediately meet the turbocharger at its outlet which increases thermal efficiency. A standard particulate filter can then be fitted further downstream under the floorboard, also a newer technology with a gasoline engine.

Construction is lightweight of course, utilizing and aluminum block and head. The structural lower crankcase cover is an innovative combination of cast aluminum and composite. Most of the ancillary external components such as the intake manifold, valve cover assemblies are also composite.

Looking around the engine compartment itself in our GLE Coupe, all of the major components are easily viewed and appear to be easily services. The oil filler cap and filter are right on top at front for example.

With the engine cover removed, you can see considerable heat shielding surrounding the turbocharger, catalyst and exhaust system components. Plastic covers on either side of the upper firewall sections conceal high-voltage electrical components but a 12-volt access point is provided. Multiple batteries both 48-volt and 12-volt and hidden under seating and the rear floorboards.

All variations of the 3.0-liter M 256 are produced in Untertürkheim, Germany. In the case of our AMG GLE 53 Coupe test vehicle the engines are shipped to Vance, Alabama where the vehicle itself is assembled.