M133 – The First 4-Cylinder Turbo Mercedes-AMG Engine Explained

AMG was first established by a couple of ex-Mercedes employees as an independent engineering firm specialized in racing engines. They were taken over in 1990 by Daimler, yet the pedigree remains to this day, even if their performance cars are now primarily for the road. Mercedes has always been direct and ambitious with the way it offers performance models, preferring to sell first and ask its customers questions later. This is why they have so many AMG cars, much more than Audi can offer RS models, and most are doing quite well. Yet it was an Audi RS that gave them the cold sweats. The RS3 was established as THE powerhouse of the hot hatch industry, but Mercedes could never rival it. That’s because previous generations of the A-Class had uninspiring performance and a short design that didn’t leave much room for performance tech to be installed. The arrival in 2012 of the third-generation A-Class, a much larger compact measuring about 4.3 meters, and the light MFA platform underpinning it changed all that.
AMG has been focusing mainly on their M156, a 6.2-liter naturally aspirated V8, and the M157, a 5.5-liter V8 BiTurbo. Yet when they designed their very first four-cylinder engine, none of these proven V8 proved a suitable building block. Instead, AMG started with another engine, the M270 straight-four turbo petrol unit used by the A250. In stock form, this 1,991cc engine makes 211 PS (208 hp) at 5,500 and 350 Nm of torque (258 lb-ft), respectable but hardly a killer. In order to be taken seriously, the M133 needed to be more powerful than the RS3, a tall order considering it has one cylinder and 0.5 liters of displacement less. The new A-Class and the 211 PS turbo engine powering it prove suitable starting blocks for a car of many firsts. The A 45 AMG has is a compact model, based on FWD architecture, powered by a four-cylinder engine that’s mounted transversally, all things that have never been done by AMG, but all necessary to enter the hot hatch market. But why? Why did a company like Mercedes, who makes the SLS and the S-Class, need a car like this. Because they believe they can sell more of these four-cylinder monsters than they can the C63 AMG. The A 45 will be followed soon by the CLA 45 AMG, and maybe even the B 45 AMG and a new compact crossover called the GLA 45 AMG. The market case for both these cars is being analyzed and prototypes have already been built.
The M133 is quite technologically advanced. The whole package only weighs 148 kilograms because most of the components are made from aluminum. The engine features spray-guided direct petrol injection via piezo injectors positioned centrally in the four combustion chambers. The four pistons have an 83mm bore and 92mm stroke, with a surprisingly low compression ratio of 8.6 to 1. The M133 revs to 6,700 rpm, but achieves its best performance between 5,000 and 6,000 rpm, where most of the power and torque is.
Like most of its rivals, AMG solved the problems created by turbocharging an engine by using a twin-scroll system that give you a more spontaneous build-up of charge pressure, making effective use of exhaust gas back pressure, exhaust gas temperature and exhaust gas impulse. The turbo uses maximum charge pressure of 1.8 bar, a significant figure that was needed to ensure high output from such a small engine. Maximum derestiction of exhaust flow is ensured by an AMG Performance exhaust system with exhaust flap. The flap was engineered after the one used on the SLK 55 AMG and continuously adjusts its angle based on driver input, load status and engine speed, all based on a specific ECU map. The double-declutching function during downshifting and the interruption of ignition and injection during upshifting under full load produce that distinctive popping sound when the M133 is pushed hard.
While the exhaust shares a little with the SLK, the cooling system was engineered with components from the AMG halo car. The SLS AMG donated its low-temperature circuit that additionally deployed for air-water charge air cooling of the M133 four-cylinder turbo engine. The air from the cooling surface at the front is helped by an additional cooler in the wheel arch (presumably the left).
An engine oil to water heat exchanger attached to the side of the oil filter housing is a clever way engineers found to keep oil cool without adding too much weight. The amazing thing is that because the engine belongs to the BlueDIRECT family, it does all this with emissions of just 161-165 grams per kilometer and fuel consumption estimated at 6.9 to 7.1 l/100km. Better thermodynamic efficiency is achieved through combination of multiple fuel injection and multiple spark ignition, in turn reducing fuel consumption. Unlike the other AMG engines, the M133 is built at the all-new, state-of-the-art Mercedes-Benz engine production plant in Kölleda, where all BlueDIRECT four-cylinder engines are built for the A- and B-Class models. In typical AMG fashion, the A 45’s engines are built by one man who signs his name on the engine filter, a hallmark for production quality. Highlights of the tech used to build it include a gravity-die sandcast all-aluminum crankcase, weight-optimized crank assembly with forged steel crankshaft and forged pistons with friction-optimized piston rings plus NANOSLIDE cylinder wall technology.