Propane injection(fumigation)......
http://www.ultimatecarpage.com/forum/showthread.php?t=7147
In the car, now called C 111-IID, the
OM 617 LA engine developed as much as 190 hp, With a Garret turbocharger and an intercooler, , as opposed to the 80 hp output of the production engine which powered the Mercedes-Benz 240 D 3.0 (W 115, Stroke Eight) and, at a later stage, other models. In June 1976, the C 111-IID reached spectacular speeds on the test track at Nardo near Lecce in Italy. In the course of 60 hours, four drivers established a total of 16 world records – thirteen of these applying to diesel-engined cars and three to cars in general, irrespective of their type of engine. During the tests, an average speed of 252 km/h was recorded, and Mercedes-Benz proved impressively that diesels also have sprinter qualities.
Second career as a record-breaking car
The success of the sparsely modified C 111-II in Nardo spurred the developers on to new heights. This time, they did not create a design study for a road-going sports car but a thoroughbred racing car for the sole purpose of establishing speed records: the C 111-III. The new car was built in 1977; it was narrower than the first C 111, had a longer wheelbase and perfect aerodynamic properties, thanks to complete streamlining and rear airfoils. In 1978, the C 111-III lined up at the start in Nardo. Once again, a diesel engine growled under the silver-painted plastic bodywork.
While this engine had been derived from a production unit, it had been tuned to develop 230 hp and gave the streamlined car a top speed well over 300 km/h. With this Silver Arrow, Mercedes-Benz established nine absolute world records in the late 1970s.