Understanding the V6 and V8 Biturbo Engines
Mercedes-Benz is known for its line of luxury and sport-touring cars. Well-refined with plenty of punch in the engine department, big Mercs have traditionally featured big engines. In today’s world, though, things are slightly different – increasingly, the carmaker now employs turbos to make up for displacement.
Mercedes introduced its first V6 in 1997, a 90-degree single-overhead-cam, three-valve-per-cylinder, twin-spark-plug design (M112). The design architecture was shared with the subsequent M113 V8 to share some components between the V6 and V8 engines and reduce costs. That’s where things got wild. There are now more Mercedes and AMG variants than most technicians can keep up with, so we’ll focus on the late model twin-turbos.
AMG began as an independent engineering company that specialized in performance upgrades for Mercedes-Benz vehicles. But DaimlerChrysler came knocking and took a controlling interest in 1999, and then became the sole owner of AMG in 2005. Through the early 2000s, AMG focused more on supercharged V8 and V6 engines, but the company officially abandoned this technology by introducing the naturally aspirated 6.2L M156 V8. In 2006, the company announced it would use turbocharging rather than superchargers for higher output over naturally aspirated versions. In 2011, AMG released the M157 5.5L Biturbo V8, replacing the M156 in its full-sized cars such as the S-Class and CL-Class.
The M157 V8 features direct fuel injection and twin turbochargers and produces 577 hp with a peak torque of 664 lb.-ft. between 2,000 and 4,500 rpm. Unlike the M156 naturally aspirated 6.2L V8 developed entirely within AMG, the M157 is based on the M278 used in the regular M-B S-Class and CL-Class models. The M157 gets 25 percent better fuel economy than the M156, so it avoided the dreaded U.S. Gas Guzzler Tax for the first time, despite having 47 hp more. The M157’s increased torque from both the standard and performance packages allowed the engine to be shifted into a taller gear sooner, keeping rpms and fuel consumption to a minimum; it also uses a start/stop “ECO” mode to save fuel. The 5.5 L V8 Biturbo models carry the “63” model designation, shared with the 6.2L V8 (naturally aspirated) models.
In 2010, the M278 V6 replaced the previous M273 V8 engines under the hood of the E-Class, S-Class and GL-Class models. The M278 is based on a 4.7L version of the M273. Both engines share the same diecast full aluminum cylinder block with 90-degree V-angle and Silitec low-friction cylinder liners. The bore size, stroke and bore spacing are identical. The M278 has new pistons with an increased compression height of 2mm. The connecting rods are 2mm shorter to preserve a compression ratio of 10.5:1. The oil pan is two-piece diecast aluminum. The vane-type oil pump is driven by the crankshaft and regulated by a bush roller chain and chain-drive integrated gear for a two-stage chain drive system.
There are aluminum cylinder heads on each bank with four valves per cylinder and two overhead camshafts. Each camshaft is equipped with hydraulic vane-cell adjusters for the variable valve timing system, which has an increased adjustment range. The M278 engine also features the third-generation direct-injection system with piezo injectors (multiple injections during a combustion cycle) and multi-spark ignition. The high-pressure pump is located at the back near the right intake camshaft and drives. The pressure supplied to the rails is between 1,700 and 3,000 psi.
Like its predecessor, the M278 4.6L V8 is a twin-turbo engine. Each cylinder bank has its own turbocharger with a vacuum-controlled wastegate valve. The small Honeywell turbochargers produce up to 13 psi boost pressure. The water-cooled charge air cooler is integrated into the intake manifold and keeps the air temperature at less than 160 degrees F. Engine systems are controlled by the MED17.7 engine control unit (ECU).
Mercedes introduced the latest 4.0L M176 V8 engine family in 2015. The M176/M177/M178 V8 engine family replaced the M278 engine and M157 engine lineup. This V8 engine is essentially two M133 (inline-4) engines sharing one crankshaft with the twin-turbocharged BorgWarner turbos positioned between the cylinder heads in the “hot-V” configuration. The injectors are Bosch’s new piezo-electric direct fuel injectors, delivering five injections of fuel in the combustion cycle. The M177 and M178 variations are used in Mercedes-AMG vehicles, and the M176 is used in standard models, including its SUVs. In 2019, the M176 employed a 48V system that produces 22 hp and 184 lb.-ft. of torque by itself.
The M177 found in the Mercedes-AMG C63 uses wet-sump lubrication compared to the M178 with a dry-sump system. In the C63 and GLC63, the turbos are single scroll, but the E63 and S63 use twin-scrolls and a different exhaust manifold. The twin-scrolls also employ cylinder deactivation. These engines are also shared with Aston Martin for the DB11 and 2018 Aston Martin Vantage per a Daimler AG agreement.
Mercedes M276 Biturbo V6 engines are considered reliable and relatively trouble-free. However, there are reports that the two-stage chain drive system has insufficient oiling issues, which causes them to wear quickly. Oiling and chain issues go hand-in-hand in many Mercedes Biturbo applications because the oil plays such an essential role in the timing system. Following recommended oil change intervals is imperative to keep these engines running their best for years to come.
The 3.0L M276 DELA30 engine released in 2013 uses the same architecture as the 3.5L V6, but with a reduced bore and stroke at 88 mm x 82.1 mm. This DELA30 engine used twin IHI turbochargers, providing a peak boost pressure of 26 psi. In 2016, Mercedes introduced a higher- output version DE30LA AMG with a lower compression ratio of 10.5:1, so the turbos could be tuned for more boost. The Biturbo version of the 3.5L M276 V6 – the M276 DELA35 engine – replaced the DE30LA in 2014. The DELA35 also features a 10.7:1 compression ratio, direct injection and twin IHI turbochargers. Despite the larger displacement, using lower boost pressure made these engines less thirsty than their 3.0L predecessor.
Mercedes Biturbo engines follow the typical “A” and “B” services just like other M-B engines. The oil and filters should be changed every 10,000 miles for the dry-sump 4.0L, which holds 7-12L of oil, depending on the model. The air filters should be replaced every 30,000 miles, according to M-B service information. The spark plugs must be replaced at 50,000 miles. Misfires have been reported on several Biturbo variants, so following the spark plug service interval will help alleviate these concerns.
A technical service bulletin (TSB LI54.21-P-062006 Version 10) was reissued on July 11, 2019, due to cylinder-specific concerns and random misfires. The bulletin provides important information for all Mercedes-Benz technicians. The misfire detection and isolation methods described in the document apply to many engines and diagnostic procedures. There’s an insightful section on spark plug electrode inspection and how to read the misfire monitors.
The bulletin illustrates a few solutions for misfires on the Biturbo V8. The first solution is to check the coils to ensure they are the updated part number A 177 906 95 00. The next is to make sure you’ve updated the software in the VGS, PTCU and FSCU control units. And, finally, M-B advises checking the grounds on the body for the ignition system. The grounding stud was painted on some vehicles. As a side note, TSB LI03.10-P-067389, issued November 11, 2017, discusses brass shavings in the filter for AMG engines. The shavings are not brass, but yellow paint applied to the connecting rod bolt caps by the AMG engine builders.
Mercedes tightly packages the turbochargers and intake manifolds on the Biturbo engines to make what would typically be an easy repair or maintenance job take much longer. You will have much more labor time for the same job on similar engines that are packaged differently. That said, these are state-of-the-art and precisely what you’d expect from a company like Mercedes. There are rumors that the M177 may be the last of the V8s for the company, and the next versions will be turbocharged inline-fours with hybrid battery power. We’ll keep you posted.