After the C-111-I Concept was introduced in 1969, the C111-II made its appearance at the 1970 Geneva Motor Show prompting interested parties to send blank checks to Stuttgart to secure one of these cars for themselves.
This last Mercedes C-111 with a rotary-piston engine from this series was the four-rotor DB M950 KE409 of the C 111-II in 1970. It developed 350hp and gave the car a top speed of 300 km/h and accelerated from standstill to 100 km/h in highly respectable 4.8 seconds. However, the problem of the Wankel engine's poor degree of efficiency was not to be overcome with technical modifications. And since the pollutant content in the exhaust gas of the Wankel engines was also too high, Mercedes-Benz discontinued work on this type of engine in 1971. Afterward, Mercedes turned to Diesel experiments for the second C111-II (the C111-IID) and third C111 (C111-III).
In 1976, Mercedes-Benz introduced the C111-IID powered by a three-liter naturally-aspirated compression-ignition engine with five cylinders in the C 111-II for the first tests. In the car, now called C 111-IID, the OM 617 LA engine developed as much as 190 hp. An average speed of 252 km/h was recorded, and Mercedes-Benz proved impressively that diesels also have sprinter qualities. (wikipedia, conceptcarz.com & carsvn.blogspot.ca)
1970 Mercedes-Benz C-111-II (Rotary Engine) Concept
1976 Mercedes-Benz C111-IID (Diesel Engine) Concept
(Photos from autowp.ru, conceptcarz.com, netcarshow.com & carsvn.blogspot.ca)