I'm not entirely sure what to call this particular record-setting prototype, so I'm going with what is written on the car.
Opel has a slightly schizophrenic past—and, if I'm being honest, present and future as well. They may well owe their survival to the long arm of General Motors, but indications are that Opel is perennially an also-ran in Europe. Growing up, I'd buy Evo Magazine and any other overseas car publications I could get my hands on, and read many group comparisons where Opel vehicles finished, generally, anywhere but first.
The company is one of the more 'general' European car companies, with vehicles as diverse as commercial trucks and small city cars fronted by the company's "Blitz" logo—donated, fittingly, from the logo of its heavy Blitz truck. This lack of specialization may have been part of the reason they are (usually) a good fit with General Motors.
Being unspecialized and in Europe gave Opel a front-row seat to an emerging technology: diesel engines. Sure, Rudolph Diesel had built his prototype engine before 1900 and the first passenger car applications began to enter production in the mid-1930s, but the engines were still very much a novel approach to powering a passenger vehicle well into the '70s.
Stationary diesel engines, engines for watercraft (including submarines!) and large motors for commercial trucks have been some of the most long-lived applications of 'oil-burning' technology, and its experience with diesel in its commercial vehicles left Opel well-placed to offer a strong diesel motor for its passenger cars.
In 1972, cutting-edge meant a 2068-cc four-cylinder diesel engine for its upcoming Rekord D family sedan, in a bid to capture some of the commercial taxi market from rivals Peugeot and Mercedes-Benz. It would be the first time a diesel engine would be offered in the Rekord.
Because "COME BUY OUR DIESEL TAXI" is a terrible way to market a car, Opel needed something a bit more…racy.
By adding a turbocharger, power from the Rekord D diesel engine was increased to 95 horsepower from 60. Increased heat and pressure were addressed by strengthening internal components, including stronger Mahle pistons and harder valve seats. From the parts bin, the engine was mated to—reportedly—a Holden Commodore transmission.
Dropped into the company's roughly 455 kg (1000 lb) GT sports car, the hopped-up diesel engine's performance was increased by virtue of even more slippery bodywork—including a sexy Plexi dome for its driver.
Doing a Google Web Search on the car will tell you little about its performance or records, even from Opel—the carmaker only says, "A modified Opel GT with a new Opel diesel engine achieved two world and 18 international records. On the test track Dudenhofen the vehicle reached a top speed of 197.5 km/h (122.7 mph)."
And that's it. I couldn't find any published records of the car's performance from Opel or General Motors—thankfully a small French enthusiast website had a chart, which I'd love to reproduce for you here…but I looked at the numbers and most of it is hard to relate to.
One particular record stood out, though: an average speed of 190.880 km/h (118.6 mph) over 10,000 km (6213.7 miles). As far as I'm concerned, the team of Marie-Claude Beaumont, Henri Greder, Paul Frère, Jochen Springer, Giorgio Pianta and Sylvia Österberg earned their keep!
Opel still trots the car out for heritage events, often used to demonstrate the company's diesel prowess.