Conversion work

Generations in conflict

•	Chosen: the base vehicle was a 190 E 2.6 Sportline built in 1992
•	Borrowed: sump from the Sprinter, differential from the C-Class
•	Tricked: electronics fool the engine into thinking it is in a test bench 
environment

"No, I can't say it was a real bargain", says Peter Lehmann, reflecting on his purchase of the 190 E 2.6 which provided the basis for the unusual conversion. "After all, the W 201 has long since gained collector status, and this example dating from 1992 was in particularly good condition." Lehmann knows a thing or two 
about the 190-series: as a Mercedes-Benz engineer responsible for the design and realisation of show cars and concept cars, and as the team leader for the conversion work, he privately owns no less than three 190s, ranging from the entry-level variant with its frugal 1.8-litre engine to the potent Evo model.

The small team that installed a new diesel power unit into the old 190 body within the space of a year also included two other, equally staunch fans of this model 
series. And they were not alone in their enthusiasm: "Almost every time the 190 was left in our workshop overnight, there was a note attached to it next morning asking if it was for sale", says Lehmann. But it was not, and it has meanwhile 
become a priceless one-off example.

Packaging: what doesn't fit is made to fit

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 OM 651, maintaining the weight balance between the front and rear axles. Moreover, the braking system 
of this former 160 hp 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, taut suspension setup which could be left unchanged.
The usual day-to-day occupation of the conversion team was to look well into the automotive future with concept cars. This time it was a matter of resolving the past, however. 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 OM 651 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.

Electronics: if it does not exist, it is simulated

"The greatest challenge during this project was not in fact the hardware, but 
rather the electronics", says Peter Lehmann. This because the 190 did not yet have a CAN-bus as a data transfer system. In the current C-Class with its state-
of-the-art 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. This is what enabled the OM 651 to spring to life, and it performs its duties with the 
usual quietness and refinement under the bonnet of the W 201.

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", Lehmann enthuses. "The modern diesel is easily able to cope with the 190. This level of muscular torque was simply unimaginable at the time, likewise the amazingly low fuel consumption." 

There were other things beyond the wildest dreams of the engineers developing the W 201 at the end of the '70s, for example the digital speedometer or four-channel ABS. "With its uncluttered design, the 190 appears timeless and drives very well indeed. Nonetheless the technical progress made in automobile engineering over the last three decades was our constant companion during the conversion work", Lehmann concludes.