Mercedes Makeover

In discussion groups, pubs and wherever car enthusiasts gather, the topic is sure to come up.

“How good would a car be that uses the lighter and smaller body of something say fifteen or twenty years old, but fitted with a current engine and transmission? Sure, safety and room would both suffer, but think about how great the performance would be!”

Well, incredibly, a major car manufacturer thought just the same thing. The resulting old-body-with-new-engine isn’t a car that will ever be released to the public, but it very clearly shows the results of such a swap - try 0-100 km/h in 6.2 seconds and 4.9 litres/100km!

And, making it even more interesting, the chosen engine revolves around the technology that has achieved the greatest advancement in the last few decades – diesels.

Not What it Seems...

From the outside it looks just like a more than 20 year-old Mercedes 190, tens of thousands of well-preserved examples of which can still be seen on Germany's roads. But pressing the accelerator tells a different story: equipped with the current OM651 common-rail engine developing 150kW, the Mercedes 190 D BlueEFFICIENCY shows the full potential of this new four-cylinder diesel engine.

With a maximum torque of 500Nm between 1600 and 1800 rpm, this experimental car has more than twice the torque of the most powerful model in the old W 201-series. The 190 E 2.5-16 Evolution II, which was presented in 1990 and produced as a homologation model for the Group A DTM touring cars, had “only” 245 Nm.

The 190 D fitted with the current engine accelerates from 0 to 100 km/h in 6.2 seconds - managing this sprint no less than 11.9 seconds faster than a contemporary 190 D. And yet the original 190 D was praised for its performance and refinement....

The differences between the two diesel generations are even more impressive when it comes to fuel consumption: despite the significant increase in output from 54kW (OM 601, 1988) to 150kW (OM651, 2009), the new engine in the old body consumes just 4.9 litres per 100 kilometres (NEDC) instead of the 7.3 litre figure for 1988.

The Swap

The 190 E 2.6 selected for the conversion work was a good choice: its six-cylinder power unit weighs around the same as the modern OM651, maintaining the weight balance between the front and rear axles. Moreover, the braking system of this former 119kW model was already robust enough to keep very many more, modern diesel horsepower in check. As a Sportline version, this 190 also possessed a sporty suspension setup which could be left unchanged.

The first challenge was that no CAD data existed for the 190. As used to be the practice, drawings of the engine compartment and engine were therefore transferred to see-through paper, then superimposed. As everything seemed to fit reasonably well, the body dimensions were accurately measured. The resulting figures were reconciled with the engine data to identify any potential collision points.

And packaging problems there certainly were. The steering would have passed straight through the sump, for example. A solution was found by consulting colleagues in the commercial vehicle sector: the sump of the Mercedes-Benz Sprinter was a good fit. The Sprinter is incidentally a distant relative, for the van is also available with the modern OM651 four-cylinder common-rail diesel engine.

The adaptation work did not end there, however. The transmission tunnel of the 190 had to be widened to accommodate the current six-speed transmission, and in the case of the rear axle differential, the team had recourse to the replacement parts range: the differential of the 3.2-litre W 203, i.e. the predecessor to the current C-Class, proved suitable.

But the greatest challenge was the electronics, primarily because the 190 did not yet have a CAN-bus as a data transfer system. In the current C-Class with its OM 651 engine, more than one dozen control units are in constant communication with each other to coordinate their respective tasks. The car will not start without the right signals, as the electronic ignition lock acts as a link between the engine CAN-bus and the interior CAN-bus.

So the team creating the 190 D BlueEFFICIENCY came up with a clever idea: they fooled the engine into thinking it was on a test bench. The appropriate signals are sent by a box of electronics roughly the size of two shoe-boxes in the boot.

But the next problem was not long in coming: for the car to operate as it should, the electronics required ABS signals. Turning wheels cannot be duplicated even on a virtual test bench, however, so once again the electronics specialists were called for - and now the ABS signals are likewise simulated.

"The driving experience is really unique", says Peter Lehmann, team leader for the project. "This level of muscular torque was simply unimaginable at the time, likewise the amazingly low fuel consumption."

Original Specs Comparison

Model series	W201 (Saloon)	W204 (C-Class Saloon)
Sales designation	190 D	C 250 CDI BlueEFFICIENCY
Start of production	1988.09	2009.06
Engine model	OM601.911	OM 651
Combustion process	Diesel	Diesel
Number of cylinders - (rotary engine discs)	4	4
Engine type	In-line	In-line
Overall displacement (effective) [cc]	1997	2143
Bore [mm]	87.00	83.00
Stroke [mm]	84.00	99.00
Compression ratio	22.00	16.20
Rated output [kW]	53.0	150.0
Engine speed at rated output [rpm]	4600	4200
Max. torque [Nm]	123	500
Engine speed at max. torque [rpm]	2800	1600-1800
Crankcase material	Grey cast-iron	Grey cast-iron
Cylinder head (rotary engine housing) material	Aluminium alloy	Aluminium alloy
Cylinder liners	Grey cast-iron, dry	none
Cylinder spacing [mm]	97.0	94.0
Balancing of masses	Counterweights	Counterweights+ 2 balancer shafts
Gas cycle control	Overhead camshaft (OHC)	Overhead camshafts (DOHC)
Camshaft drive	Duplex chain	Chain/gear-wheel
Number of camshafts	1	2
Valve operation	Bucket-type tappets	Rocker arms (cam followers)
Variable intake control	no	no
Variable exhaust control	no	no
Valves per cylinder	2	4
Intake type	Manifold assembly	Manifold
Engine charging	no	2 turbochargers
Charger manufacturer	no	Borg Warner

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