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Opel GT In Production

"Opel GT in Production"
by Jean Bernardet

Part I & Part II

This is the first part of the true story of six long years of the GT project development at the Opel Styling Center. It in fact refers only to its stylistic gestation period and does not include, for lack of space, any account of the later stages devoted to body structure calculations and to the development of production methods and equipment.  These have received active contributions from Messrs. Chausson and Brissonneau & Lotz who are responsible, respectively, for sheet metal presswork/assembly and paint/trim operations of this new Opel body Its structural characteristics and manufacturing techniques—in the Paris and Creil plants of the two leading French body builders—will be described in Part II.


For the time being, the one and only character on the stage of this story is the Opel Styling Center. We know perfectly well that this sort of technical literature is by now a familiar topic to most of the readers of our magazine; the development of a new prototype seldom offers, if ever, any truly novel aspect to a particularly keen and interested reporter.  Unless, as in this case, the story is put together, piece by piece, on the basis of news and illustrative material supplied directly from the source; and then, it will really be worthwhile to tell once again the old story of how a new body sees the light. This stated, you may consider this article as an exclusive, "official" report by the Opel Styling Center on its latest offspring. Chuck Jordan, the present Director of Opel Styling, has contributed directly to the writing of this article.

Opel styling is not an abstract concept, it is people. Designers, creative engineers, sculptors, technicians and craftsmen. The responsibility of this highly specialized group is the design of future Opel products. In addition to the development of future production vehicles according to the product program, a great deal of effort, in the research and advanced design studios is directed toward the design of basically new vehicles for a particular purpose or to take advantage of particular market opportunities. Imagination, innovation, and dissatisfaction with things as they exist are key assets of the Opel styling organization.  These characteristics were responsible for the start of the Opel sports car program in the Fall of 1962.

Even earlier than this date, a great deal of thought and conversation had already gone into the idea of an Opel sports car. Among the several important conclusions were the recognition of the existence of an international market for a German sports car, well designed, well built, capable of good performance and at the same time inexpensive: the price was to be set in the DM 10,000 (@$2500. USD) class. The English and Italians had sporty cars in this area but there were few genuine sports cars. Secondly, it was felt that a care needed to be designed that would add youthful sporty overtones to the overall Opel image.

Planning was well timed and even though little was known of this program outside the Styling Center, from the beginning the car was intended to be an Opel show car at the 1965 Frankfurt Auto Show. Opel designers thought that cars of this nature stir up a great deal of public interest; if the public reaction and enthusiasm are strong enough, the Opel management will be encouraged to produce a prototype of this kind. If we do our job well, Opel will finally have its first production sports car.

The design goals for this car were carefully evaluated and defined. The Styling Center would create a total car design, new from the ground up, that would meet the functional performance and size requirements of a genuine sports car. Its body would be shaped with integrity and carefully calculated purpose so that the result would be both functional and handsome.

The first step in developing a GT car was to delineate its architecture. Beginning with the passenger compartment, low comfortable seating for two was laid out utilizing the best human engineering principles. From this point of departure, good interior roominess was obtained by reaching a satisfactory compromise between the critical dimensions surrounding the occupants and the requirement of minimizing aerodynamic drag through a reduction of the greatest cross-sectional area.

The mechanical components of the car necessary to complete eth architecture—the engine, wheels, drive train and rear axle—were placed around the passenger compartment with particular attention to their effect upon weight distribution, performance and handling.  Wheel house volume was kept down to a minimum. Between the rear wheel houses, just behind the seats, space for luggage, the spare tire and the gas tank was provided.

Having thus set the arrangement of inner spaces in the vehicle basic architecture, the second design stage of giving shape to the body began. The advanced designers and Styling research engineers developed a number of new body configurations over this established architecture, as established. Scale models were constructed and studied and the most promising designs were developed full size. The final shape of the car grew from the designer's creative and aesthetic sense influenced by the architectural parameters established early in the design process and the many lessons learned in the wind tunnel.

Remembering that the design goal called for a functional and handsome shape with integrity and purpose, a new character was developed for the body which was bold and exciting and at the same time harmonious and tasteful. All qualities which should wear well over the years.

As it took form under the modeler's hands, the body grew gracefully, without excessive weight or bulk and took a form which its designers feel has an appropriate and sincere sports car character.

While the full size clay model was being developed and refined to the exacting requirements imposed by the pre-set layout of the car's mechanical components, an accurate interior seating buck was completed to carefully evaluate the seating comfort, interior roominess, and ease of entrance and exit. In this buck, a straightforward, business-like interior design was developed. It was characterized by a functional, wide instrument panel, with a console and convenient controls, utilizing principles of human engineering and styling of instrumentation and controls was completed. After the total design was finished and judged correct a running prototype was constructed in the Opel Engineering shop.

This was the show car—called the Opel GT—introduced at the Frankfurt Auto Show in 1965.  The Opel GT was later shown in Paris, Turin and New York and, just as the Styling Center had foreseen, it stirred up a great deal of interest and acclaim. The question heard most was "when are you going to produce this car?"

After the automobile show circuit, a certain silence began to shroud this sports car project for then it was the time to reach a decision on its future. Opel book-keepers, who sport particularly well-sharpened pencils, had very little hope indeed. But, fired by the determination to put the GT in production, the Styling and Engineering Departments, together, quickly discovered that it could be built on the Kadett underbody  -- the same structure that won so many victories for the Rallye version in sports events such as the MonteCarlo Rallye, Tour d'Europe, etc.

All Kadett and Rekord power plants, transmissions, axles, brakes, and other mechanical components could be used. The remaining questions centered around tooling the body and finding facilities in which to build it. The hope of producing the Opel GT appeared to be promising.

One major conflict existed with the use of the production Kadett underbody. The Frankfurt prototype was designed with the engine as far rearward as possible for good weight distribution.  The production Kadett engine location, straddling the front suspension cross member, is fine for a 5-passenger sedan but not for a 2-passenger sports car. There was a group at Opel at the time that felt that the position of the engine would have little effect on the handling and performance of the car. On the other hand, the Styling Research engineers, and sports care enthusiasts within Opel, insisted that the GT be the best handling sports car they could produce and the engine should, therefore, be rearward.

To settle this question, two cars were built, one with the engine in its production location and the other with the powerplant some 16 inches further aft.

These prototypes were tested under racing conditions on the Nurburgring by Porsche team driver Hans Hermann. His recommendation emphatically endorsed the rearward engine position and his judgment was respected. The integrity of the original GT architecture was maintained with a rework to the Kadett underbody to move the engine aft.

Aerodynamics was an especially important consideration in the development of this GT.  Full size testing of the Frankfurt show car in the Stuttgart wind tunnel defined the efficiency of the body shape and provided the basic data for changes to the production body design.  The different stylistic and engineering designs proposed to this end, were tested and refined in scale model form in the "small" wind tunnel of the same University, in search for the lowest drag coefficient, best directional stability and minimum lift. The wind tunnel experiments confirmed that simple, clean, smoothly flowing surfaces, with minimum offsets for glass and moldings, produced the best overall results. Some rework on the nose and the deck surfaces, with the addition of the "duck tail," were necessary to improve the aerodynamic efficiency of the Opel GT. As a result (in comment of the data published in tabulated form at the end of this article) the production body offers a drag coefficient slightly inferior to that of the Porsche 911.



The moveable headlights were also dictated by functional requirements. The low hood, and the small diameter wheels that do not require high fenders, made the legal height of the headlights a problem. The concealed headlights add to the aerodynamic cleanliness of the car, and are protected from dirt and damage when not in use.

The final full size body design in clay was developed, refined and ultimately approved by the Management after a number of reviews in the Styling outdoor viewing yard. Also the interior design was mocked up (full size) completely and accurately for evaluation, refinement and final approval. In the Fall of 1966 -- four years after the project had began—the GT production body design was put on paper and released to engineering. In the meantime, a full-size finished plaster model of the design was carefully constructed down to the last detail, with painted surfaces, glass, chrome bumpers and trim; it was the master design model. All additional production changes were also made to this model for its updating as a faithful record of the final design.

A male plaster cast was sent to Chausson in Paris who had been chosen to tool and build the "body in white."  The final color and trim details were worked out with Brissonneau & Lotz in Creil (another famous bodybuilder in the Paris area) who were responsible for the trim, paint and finish of the body built by Chausson. The completed car is assembled at the Opel Kadett plant in Bochum, West Germany.

The final production design of the Opel GT varies in a number of ways from the prototype shown three years earlier, as shown by the pictures which appear on these pages. The more obvious changes are: the higher front bumper, the addition of two air intakes above it, and the bulge on the hood made necessary to clear the carburetors. The windshield wiper pivots are now hidden under the hood. Whereas the concealed headlamp mechanism on the prototype was of the pop-up variety with rectangular lamps, the production car features round headlamps which rotate 180 degrees out of sight about their longitudinal axis: the result is better appearance when the lights are up.

From the rear view certain other changes are noticeable: air outlet slots for cockpit ventilation located above the redesigned back window; the rear bumper has been simplified and overriders added for further impact protection. In the interior, bucket seats now offer improved lateral support; seat backs have built-in headrests. The wealth of instrumentation has improved notably; all controls are clustered in the central console.

Production of this new German Gran Turismo car began in October 1968

"Per 17 U.S.C. Section 107 and related statutes, the presentation of excerpts of materials relating to Opel model vehicles, is intended for educational and research purposes only."

Go to: Part II

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