The Mercedes C-111 Concept.

The C111 was a series of experimental automobiles produced by Mercedes-Benz in the 1960s and 1970s. The company was experimenting with new engine technologies, including Wankel engines, Diesel engines, and turbochargers, and used the basic C111 platform as a testbed. Other experimental features included gullwing doors and a luxurious interior with leather trim and air conditioning.
The first version of the C111 was completed in 1969. It used a fiberglass body shell and had a three-rotor direct fuel injected Wankel engine (code named M950F) mounted in the middle. The next C111 appeared in 1970. It used a four-rotor engine producing 370 hp. The car could reportedly hit 180 mph.
The company decided not to adopt the Wankel engine and turned to Diesel experiments for the second and third C111. The C111-IID produced 190 horsepower and was based on the 240D 3.0 W115 model OM617 engine. The C111-III was powered by a 230 horsepower @ 4,500rpm straight-5 OM617 turbodiesel which broke nine diesel and gas speed records. With more aerodynamic bodywork that gave it an air drag coefficient of .191, the C111 eventually hit 200 mph at Nardò in 1978, and averaged 14.7mpg@ 195.4 mph over a 12 hour cruise. A later 500 hp 4.8 L twin KKK-turbocharged V8 version set another record, with an average lap-speed of 250.958 mph. It was achieved by Dr. Hans Leibold in 1 minute, 56.67 seconds on May 5, 1979.
Mercedes-Benz introduced the C112 at the Frankfurt Motor Show in 1991 as a production sports car. It used a 6.0 L V12 engine mounted in the middle. But after accepting 700 deposits, the company decided not to proceed with production.