We already spoke on this site about the new generation Mercedes 4-cilinder Diesel engines, and a recent spell at the wheel of a silver grey Mercedes C-class 250 in AMG livery amply proved that the oldest car manufacturer in the world has gone a very long way in improving Diesel engine technology still further. The twin-turbo engine showed us how a modern Diesel engine can perform, and that it can effectively re-invent itself again…

Hans Knol ten Bensel

That small extra turbo...

The beauty of this power unit lies in its uncanny behaviour at low engine speeds in city crawls. The engine can be driven smoothly a 1.000 rpm, and it picks up swiftly and beautifully from this revs, with a very subdued engine note adding to the very relaxed and “zen” driving atmosphere. Relaxed, because one feels that a short blip of the throttle will propel you instantly and without any hesitation into higher speeds, and it is this pleasant feeling of having always ample power ‘at hand’ which adds to the unique driving pleasure.

The engine picks up powerfully from very low revs indeed...

The torque band shows all this clearly, with not less than 500 Nm available from as low as 1600 rpm, with a maximum power output of not less than 204 hp or 150 kW reached at 4200 rpm. Torque does not drop significantly at higher revs, thanks to the second turbo getting to work in the medium rev ranges, and fully taking over from the small H(igh) P(ressure) turbo which does all the low-speed work.

The technical wonders are neatly covered to the eye... but they work!

The small  HP turbine has a diameter of 38.5 mm and is positioned directly in the exhaust manifold. The flow of exhaust gases flows through this turbine first, causing it to rotate at speeds of up to 248,000 revolutions per minute. Result: zero turbo lag.

When starting off, the entire exhaust, the whole exhaust stream flows through the HP turbine, meaning that all of the energy contained in the exhaust gases is directed towards propelling the HP turbine only.

As this would very soon prove to be too much of a good thing, a bypass duct is integrated into the HP turbine housing , and this can be opened or closed by means of a charge-pressure control flap triggered by an actuator.

The engine produces ample power in any gear... but is not afraid of higher revs, where the bursts of power are also abundant...

Downstream from the HP turbine, the two exhaust gas streams join up again, and any remaining exhaust energy drives the 50-millimetre L(ow)P(ressure) turbine at a maximum speed of 185,000 revolutions per minute.

Once the engine reaches medium rev speeds, the HP turbine's charge-pressure control flap is opened so wide that the HP turbine ceases to perform any appreciable work. This allows the full exhaust energy to be directed with low losses into the bigger LP turbine, which then does all of the turbine work. Beautiful, isn’it it?

Attention to detail: intake port shut-off for optimum air supply

Before flowing past the intake valves into the cylinder, the combustion air flows into a so-called “charge-air distributor module”, which supplies air to each cylinder in a uniform manner. Built into this  distributor module is an electrically controlled intake port shut-off, which allows the cross-sectional area of each cylinder's intake port to be smoothly reduced in size. This alters the swirl of the combustion air in such a way as to guarantee that the charge movement in the cylinders is set for optimum combustion and exhaust emissions over the full spectrum of engine loads and rev speeds.

With this excellent cylinder filling conditions being warranted right from low revs onwards, it is not surprising that the engine is not only quite frugal (an average consumption of 5.5 l/100 km and less is easily achieved) but the engine produces also CO2 emissions of a mere 138 g/km.

Tyres and AMG light alloy wheels are of course up to the task of putting all the power on the road...

And performance? This leaves of course very little to be desired. This mighty C storms from 0 to 100 in a mere 7.2 seconds, and the accelerations in the different gears are also very dynamic indeed, to say the least. Top speed is an electronically controlled 250 kph.

Commands on the central console and the display betray the know how of the manufacturer...

It seems a bit far fetched, but nostalgic car buffs as we are, my thoughts drifted, hearing the distinct 4-cilinder engine throb when accelerating hard, to what the pilot must have felt at the wheel of the white, nimble and so efficient Maybach designed 40/60 hp 4 cylinder Mercedes Simplex at the Nizza – Turbie hill climb and Nizza Speed Week, when he drove the competition home. He showed the world then for the first time that Mercedes stood for efficiency, mechanical excellence and some (very)mighty performance… 

The C-class shows the hand of the master…

The good qualities of the C-Class have already been discussed elsewhere on this site. We drove this time the sportier AMG version, with agility and roadholding to match some very high expectations indeed.

The car was very well equipped, with a full glass sun roof, amongst others. We were again very pleased with the excellent navigation and audio displays and controls. The Harmann Kardon audio system proved again its excellence. The seats are a bit narrow for your servant, but proved comfortable nonetheless.

Flawless finish and quality is also found in the leather upholstery...
 

What remains are the well-laid out controls, a bit big and hefty at first, but feeling ‘just right’ after a few hundred kilometers. The whole car breathes the car building know-how of the oldest manufacturer in the world, and we do not need to say (anything) more…

Hans Knol ten Bensel

Photographers notes: The photos were taken with the Nikon D40, hardly any exposure correction was necessary in the evening light, the 400 ASA setting was used, also few corrections were necessary in Photoshop  

This is what most drivers will see of this fast Diesel...