The Mercedes-AMG developed a naturally-aspirated, high-revving V8 engine to showcase their AMG Cylinder Management cylinder shut-off system. Though not as big and powerful as most V8 at that time, it is more efficient, as you can save at least thirty percent of fuel consumption; it is highly reliable and compact enough for a vast machine.
And with that, let’s take a deeper look at the 5.5 Liter naturally-aspirated Mercedes M152 engine.
What are Mercedes M152 Engines?
The Mercedes M152 engine is referred to as the 5.5 Liter naturally aspirated V8 engine designed for Mercedes-Benz R172 SLK 55 AMG and Mercedes-AMG R172 SLK 55. It is the third variant that makes up the trio collective of the Mercedes M278 engine family. M152 engine is an M157 variant, but it is revised by the AMG, a subsidiary of Mercedes.
This engine is derived from the 5.5 Liter bi-turbo Mercedes M157 engine. They have the same displacement, cylinder spacing, ECO start/stop system, bore and stroke, and direct injection. However, the M152 features a new cylinder head, lubrication system, and intake manifold. It is integrated with a cylinder deactivation variable displacement system for a better fuel economy, up to thirty percent better than the M113 E55 engine.
Engine Specifications and Design:
- Production Run: 2012 – 2015
- Cylinder Head Material: Aluminum
- Cylinder Block Material: Aluminum
- Configuration: V8
- Bore: 98 mm
- Stroke: 90.5 mm
- Valvetrain: DOHC four valves per cylinder
- Displacement: 5.5 L (5461 cc)
- Compression Ratio: 12.6
- Weight: 440 lbs.
- Maximum HP: 416 HP at 6,800 RPM
- Maximum Torque: 398 lb-ft at 4,500 RPM
The Mercedes M152 engine has a solid and lightweight aluminum cylinder block with a 98 mm cylinder bore, 90.5 mm piston stroke, and a 12.6 compression rating. The cylinder banks are arranged in a ‘V’ configuration with 106 mm spacing between these cylinders, same with its Mercedes M157 sibling.
Inside the bores is a cast-in Silitec (aluminum-silicon combination) cylinder liners. The Silitec liners undergo a deck plate honing process, which aids the assembled state simulation and static crankcase deformation by mounting a deck stress plate on the cylinder head.
The crankcase ventilation happens through a series of two oil separators, an impactor and a centrifuge. These guys work via a line between the impactor and left air filter.
The ventilation starts at the centrifuge through a pressure regulating valve and a check valve in partial load situations and eventually reaching the partial load branch to charge the air distributor.
The ventilation starts at the centrifuge in full load but goes to the right air filter upstream of the turbocharger via a pressure regulation valve and a check valve. Moreover, full-load vents happen between the oil separator and left air filter to the left filter upstream of the turbocharger.
The Mercedes M152 engine has a forged steel crankshaft with eight counterweights that rotates on five main bearings. To add, the machine has 146.5 mm fracture-split forged connecting rods and cast aluminum pistons with 30.1 compression height. A diamond-like coating covers the first piston ring of the M152 AMG, a technology applied on most racing engines.
The M152 cylinder head is aluminum-made with dual overhead camshafts driven by a two-stage chain drive with three gear chains; a hydraulic chain tensioner tightens each gear chain. The camshafts are made from internal high-pressure formed steel tubes with composite cams.
Furthermore, the heads have a two-piece water jacket and cooling slot between the cylinders. A hydraulic vane-cell camshaft adjuster with a control valve is also installed for a more responsive and instantaneous operation. The adjuster can adjust all camshafts instantly by up to 40 degrees relative to the crankshaft to change valve overlap.
The roller cam followers actuate the four valves in each cylinder; the hollow exhaust valves are packed with sodium for dissipating heat.
A direct fuel injection system is installed in the M152 engine. Mercedes used the same direct injection system in the Mercedes M278 engine. It has a non-return high-pressure supply with two separate fuel rails. Coming from those rails, the piezo injectors spray refined atomized fuel into the combustion chambers and can provide up to five injections per cycle.
A coupler module is placed inside each fuel injector to ensure that the piezo actuator model and nozzle module have zero clearance in the longitudinal direction. An O-ring seals the fuel feed on the high-pressure side and fills the leak line at the fuel injector. Moreover, the seal between the cylinder head and fuel injector is provided by a Teflon ring.
The AMG M152, just like the M278 and M157, has an ECO start/stop function. A start-assisted in-engine direct start function and engine stop function are combined to form a start/stop operation. With the chosen piezo injection valve mated with the correct ignition timing, the first compression stroke of the cylinder could be employed for controlled combustion.
Even though the M152 is not turbocharged, the cylinder deactivation function enables the four cylinders to shut down under low throttle loads. The cylinder shut-ff function is available at low loads at 800 RPM to 3,600 RPM. The driver can select the “Controlled Efficiency” transmission mode to manage the shut-off of cylinders 2, 3, 5, and 8.
Subsequently, the fuel injection and fuel ignition will be adjusted, closing the intake and exhaust valves. A switchable hydraulic element in the heads would drop underneath the camshaft and disconnect the valves from the camshaft to achieve this. Hence, allowing the heads to have complex oil supply bores for the hydraulic pivot elements.
The cylinder shut-ff function increases efficiency by shifting the operating cycles of the active cylinders to higher loads, thus reducing gas cycle losses. The shut-off cylinder can also reactivate quickly with a neutral effect. That means comfort in riding is not compromised, no shaking or whatsoever.
A centrifugal pendulum is installed in the torque converter of the AMG Speedshift Plus seven-speed automatic transmission to reduce unnecessary vibrations. This pendulum acts as an RPM adaptive damper that operates across the entire speed range.
The Mercedes M152 engine has additional efficient ancillary units such as a newly developed vane-type oil pump, a variable alternator, a volume-controlled high-pressure fuel pump, and an optimized water pump with second-generation thermal management. All of these additions significantly reduce the energy demand on the engine.
The power output of the M152 is 416 HP at 6,800 RPM with 398 lb-ft of torque at 4,500 RPM. The engine can be found on the 2011 – 2016 SLK 55 AMG.
Engine Tuning, Modifications, and Upgrades
Upgrading the M152 is not that hard, and we can get the best of the engine with the proper tuning and upgrades. The M152 has a lot to offer; even with the stock power rating at more than 400 HP, we can stretch that to an even bigger number.
The first you have to do is to change the camshafts to fit your personalized build. Changing the cams significantly enhances the power bands and power output. Both ways, you need to match your power and torque demand for either a daily driver or a weekend track.
You can mod your engine in three stages. The first stage involves a sports exhaust manifold upgrade, panel air filters, intake headers, and ECU remapping.
The second stage is an induction kit, high-flow fuel injectors, and fuel pump upgrades. The third stage is the major one since you will need engine balancing, upgrading your forced induction, crank and piston upgrades, as well as internals.
Putting forced inductions and remapping can gain you at least 30-40% of power and torque, but it also depends on the upgrade that you made before.
Problems Surrounding Mercedes M152 Engines:
The Mercedes M152 engine is solid and robust, far more reliable, and has few issues. I know it’s pretty evident due to the power output and abilities it can do, but even at its peak, this engine still has troubles that might be left unaddressed. We are here to talk about it.
The first is the ticking sound that comes from the valvetrain that mainly occurs on startups and cold engines. You will notice noises at about five seconds into starting, then goes away and comes back. Some owners say that this is just an oil temperature issue, but it is better to bring it to the dealer since matters like this are still under warranty.
Tune and modded M152 engines frequently suffer misfiring issues on the OEM spark plugs. In addition, a large spark plug gap combined with higher cylinder pressure may result in a blown-out spark plug.
Another one is coolant hose leaks. As the M152 engine age, its components start to degenerate, crack, and split; the hose is no exception. These are easy repairs, but beware if the leak is bad enough to cause an excessive coolant loss.
That issue will not end pleasantly as it can lead to overheating, and we all know that overheating is detrimental to the engine. When the engine lacks or is out of coolant, operations will quickly get hot, affecting the machine’s overall condition.
Don’t forget the regular oil changes on the M152 engine, particularly in heavily modified ones since they put bigger numbers than what is intended for them.
The lasting impression of the M278 family continued throughout its entire generation of engines. An economical V8, powerful, efficient, safe, mixed with comfort and luxury, fits the machine catalog.
The M152 has excellent power and torque numbers. The technology used mainly was applied on motorsport engines making the M152-fitted vehicles feel and experience the adrenaline kick but comfortable at the same time.
It is also a reliable engine since there are no significant issues, especially in the engine design department. It makes a lot of sense, though, for this engine is a product of years of expertise and revolutionized the V8 impression worldwide.