Photos from Mercedes
A few months ago, the automotive media went nuts over the M139 engine from Mercedes. It’s the highest horsepower 2.0L engine ever to go into production making 416hp. That’s 208hp/L. While being emissions compliant. With a warranty. And it can run on crappy 91 octane while doing it all. 208hp/Liter is higher than any other production car on the market and rivals 600cc sportbikes in hp/L. Mercedes dropped some pics into the internet so let’s take a closer look.
A little bit off-topic, but that electric torque gun sitting in the tray behind the engine is like ten grand. If it’s like the one I’ve used, it’s got wireless connectivity to a computer and it tracks every single fastener and the torque value attained. Of course, it also tells you if it torqued the fastener to within specification too. If you get a big red X error, the proper torque was not achieved. Smart tools like these are how to build quality standards are maintained in a manufacturing environment.
To make those big power numbers requires a lot of boost. A lot of boost on a small displacement engine means more lag. To combat lag, Mercedes uses a twin-scroll turbo. From the looks of it, I think it’s from IHI. Each turbo manufacturer does things a little differently which helps identify who made the turbo, like the joint between the wastegate actuator rod and wastegate arm. Also, the compressor housing to backplate joint. This turbo on the M139 also has ball bearings to reduce lag and improve transient response. A nice cast tubular log-ish manifold is the right mix for performance, cost, packaging space, and durability for an OEM application. My S2000 manifold concept is not too dissimilar. Check out the metal heat shield between the turbo and the plastic valve cover along with all the heat shielding underneath the manifold. I believe under the heat shielding are coolant passages. The turbo oil drain line and coolant line are also covered in insulation. Heat is thy enemy. Back to the turbo, there’s only one other carmaker using a v-band twin-scroll turbine housing with ball bearings in a production car that I’m aware of and that’s Ferrari. On the Ferrari 488, the turbos also have TiAl turbine wheels and abradable coatings on the compressor housing. The new Ferrari F8 will have a similar spec turbo. Anyway, the turbo on the M139 engine probably just slightly bigger wheels.
The use of a rotary electric wastegate actuator allows the use of a simple straight tie-rod instead of the 2-piece bendy linkage required with the use of a linear electric actuator. Electronics typically don’t like too much heat, so there’s a heat shield protecting part of the actuator. The turbine housing insulation wrap is typically seen on motorsports, but rarely on streetcars. Power = heat and the M139 is putting out a lot of hp/L…
This cutaway gives a peek at the two volutes of the twin-scroll turbine housing. Why is the entry to the catalytic converter not a simple dome? Because then, the exhaust flow would not be evenly distributed across the core and increase emissions. So, the shape of the entry into the catalytic converter is to force exhaust gasses through the part of the core on the inner side of the bend that would otherwise be bypassed due to the whole Newton’s first law thing. A couple of brackets help support the weight of that massive catalytic converter. Otherwise, all that weight would be transferred to the turbocharger and manifold and likely crack them over many heat cycles and time. Just eyeballing the size of the catalytic converter, it’s bigger than the turbo. It’s probably in the 6” diameter range assuming the inlet and outlet are around 3” diameter. Yeah, there’s no way to fit the catalytic converter under the car easily.