Mercedes Benz announced a four-cylinder engine packing 416 horsepower earlier this summer, and squeezing that much power from just two liters of displacement requires some serious engineering. Fortunately, Engineering Explained just released a YouTube video explaining how they did it.
This new AMG-tuned M139 four-cylinder will power the A45, CLA45, and GLA45. The Honda S200 set a high bar at its introduction for horsepower per liter by pulling 240 horses from just two liters. That bar has moved a few times, but now thanks to another small two-liter engine like this Benz, which cranks out 208 horses per liter, or 104 per cylinder, the bar is set quite high. The tricks that got it there are actually pretty simple. Here are a couple of the top ones.
Engine rotated 180 degrees
This one seems odd at first, but when host Jason Fenske draws the layout on his whiteboard, it all makes sense. The “cold side” of the intake tract are now all up front, with the “hot side” exhaust and turbo now located behind the engine against the firewall. Mercedes claims this layout allows for shorter intake and exhaust tracts, and since an engine is a glorified air pump, that means efficiency increases. There had better be some good insulation on the firewall, or I would predict the driver and passenger will not need thick socks in the winter thanks to the turbocharger and exhaust location.
Anti-friction bearing turbocharger
Anti-friction bearings (more commonly called roller or ball bearings) aid in helping that rear-mounted turbocharger spool more quickly. More boost at lower rpm means less turbo lag, creating a peppier driving experience. The turbo is also set up to provide 30.5 psi of boost to the intake, a significant amount of pressure for an engine to handle. Which is why Mercedes utilized a…
Closed deck engine block
This design means the coolant passages around the cylinders are not as large as they could be, which sacrifices some cooling efficiency in the name of block rigidity. This style engine casting is also more expensive to produce, but helps maintain cylinder shape under extreme cylinder pressures that high-boost engines experience.
Port and direct injection
That’s right, one injector simply is not enough for the M139 engine. Fuel is added both in the intake runner and directly to the cylinder by way of two injectors. The fuel demand is significant, so it makes sense, but as Fenske mentions, the port injection also helps keep the backside of the intake valves clean and deposit-free, which slows efficiency loss of the engine over time.
Low-friction cylinder coating
The cylinder walls of the M139 engine block are treated with a spray-in liner that Mercedes calls Nanoslide. This coating is designed to help reduce cylinder wear by holding oil in place thanks to its micro-porosity, while the friction reduction helps with fuel economy. It is also a very thin coating, which helps give these benefits without the weight penalty materials like this have added in the past.
So there you have it. A small grouping of not-so-new tech that all add up to one of the most efficient little engines to date. Is there one of these features you find particularly impressive? Be sure to tell us about it in the Hagerty Forums below.