In the late 1970s Germany’s Federal Ministry for Research and Technology launched a national program to inspire and guide car producers toward more efficient, lower-emission and potentially smaller passenger cars. This sounds like a huge challenge, and it was. But some rationality was powering the initiative.
A concentration of negative factors was steadily pressing on Germany’s automobile producers. First and foremost were the 1973 and 1979 oil crises. These highlighted the vulnerability of oil-dependent transportation. Linked with this was a growing concern over the role of the automobile in creating excess air pollution and its sister, heavy fuel consumption. This in turn raised questions about car weight and bulk—two parameters that tended to expand steadily year by year.
Known as the Bundesministerium für Forschung, BMFT for short, Germany’s Federal Ministry for Research and Technology stepped into the complex issue of forecasting the challenges and solutions of the 1980s motor vehicles looming ahead. Its in-house experts spread the word to Opel, Audi, Daimler-Benz, Volkswagen, and Porsche to probe what they proposed building for the coming decade.
They didn’t lack advice. From the BMFT flowed recommendations along the following lines:
• Minimum 20-30 percent improvement in fuel economy compared to contemporary vehicles.
• Exploration of new aerodynamic and material technologies to achieve that.
• Testing safety, handling, and comfort consistent with a modern passenger car.
• Commitment to stimulate technological innovation in the German car industry as a response to anticipated future regulatory and market pressures.
Needless to say, Porsche’s engineers assessed these objectives as right up their street. Overseeing advance development was Dusan Gruden, who also
engineered projects for outside customers. A newcomer to his team, Helmut Striebich, went back to basics. From the vehicle’s fuel, he said, 35 percent came out of the exhaust pipe, 20 percent went to cooling air or water, and another 20 percent to heat radiation. That left 25 percent for motive power. That number had to be increased.
In 1979 at Weissach, Porsche hosted a major technical seminar, the Porsche Consumption Symposium, to discuss technologies for improving fuel economy without impairing performance. One paper discussed the Thermodynamically Optimized Porsche (TOP) engine—a Gruden specialty—in which the compression ratio was increased to around 12.5:1 with high squish to ensure strong fuel/air mixing and the consequent ability to run lean mixtures when on part-load. Porsche suggested that varying the mixture strength from rich (lambda 0.85) to lean (up to lambda 1.2) according to operating conditions, would result in up to 25 percent better fuel economy.
Another Porsche contribution in the 1979 symposium included lower and much better-regulated idling speeds, an electronic technique later taken for granted. Another measure was automatic stop-start—always a good idea in principle but doomed to suffer problems until the arrival of hybrids twenty years later. Partial cylinder cut-out, running a V-8 on four cylinders when on part-load, had merit. Porsche never took this technology to production, although it provided it to other automakers.
In October 1979, Porsche’s Ing. Striebich contributed to the BMFT effort with a device that promised to squeeze more energy from the exhaust system. “The object of the invention,” he said, “is to create a drive unit, particularly for motor vehicles, in which the energy quantities and types inherent in the exhaust gases are used in such a way that the effective efficiency of the internal-combustion engine is significantly increased compared to known drive units.
Striebich envisioned extracting more energy from the exhaust “through a superimposed thermal work process in the exhaust-gas turbine of the waste-heat turbine unit. The waste-heat turbine unit comprises a compressor, a secondary turbine, and an exhaust-gas turbine, wherein the turbine blades of the exhaust gas turbine are formed by hollow blades through which the working fluid compressed by the compressor flows. This fluid expands in the secondary turbine after absorbing heat from the exhaust gases, releasing power.” The added-rotary Striebich system turned out to absorb more energy than it radiated.
A contribution of the Weissach engineers was the PDK twin-clutch transmission. It was initiated by Imre Szodfridt and Richard Hetmann in the 1960s, developed by Rainer Wüst and readied for production by Heinz Stehle. Its gear shifting was accomplished by the near-simultaneous engagement of one clutch and the disengagement of another.
This profile of an early PDK gearbox highlights the twin-clutch arrangement situated at the unit’s front housing (left side).
“The idea,” said Wüst, “was to combine the best of two worlds—the advantages in the degree of efficiency of a manual transmission and the potential for performance of full automation, which still had many weaknesses at the time. It was a huge challenge for a small department such as ours. Maybe it was naivety that helped us, but certainly our pragmatism in dealing with the challenges did—as well as our passion for this subject.”
Engineering chief Helmuth Bott decided that racing would be the best venue for the development of the PDK. Porsche’s in-house effort began in 1982 and ran through many iterations in racing applications. “Although at the moment we can’t expect racing successes,” said Wüst, “it would be sensible to enter additional races for test purposes.” It continued to be fielded in Group C racing by Hans-Joachim Stuck, accruing some successes. Not until 2008 did Porsche offer a PDK for the 911. As for the demands of the BMFT, the PDK was steadily made lighter—but it was always heavier than the standard transaxle.
The PDK was an integral part of the Type 995 that Porsche created in 1978-1979. Described as a sports-car concept for the future, in their three-dimensional study the Weissach team did its best to combine economy with performance, plus “new standards of safety and quietness”. External noise levels were at this time something of a concern for Porsche, because quantitative legal standards were being laid down for the first time. In some instances special measures had to be taken to allow the 911 to comply. The Swiss noise standards were (and to this day remain) especially severe.
Commissioned by Germany’s Federal Ministry of Research and Technology, in 1978/1979 Porsche developed a concept for the construction of a future sports car. Overall responsibility for
the effort was broad-based engineer Helmut Flegl. Development objectives for a close-coupled four-seated concept car focused on fuel economy, safety, and noise emissions. The engineers in Weissach used the 928 as the technological basis for the research prototype, sometimes referred to in archives as the “Advanced Research Automobile” or “Advanced Technology Vehicle”.
Porsche leveraged aerodynamic know-how from both its racing programs and its ongoing research into front-engine, transaxle layouts that optimized weight distribution and efficiency. The issue of its powerplant was high on the “wanted” roster. Porsche said that it had ruled out diesel and turbodiesel engines on the grounds of weight and noise, although their frugality with fuel could have offered savings in that area. Know-how in diesel powerplants was applied instead by encapsulating the engine to moderate its noise.
The idea of an engine placed centrally or rearward was explored but given up in order to offer the sort of rear-seated roominess that a 911 provided. Plans envisioned a high-compression 3.0-liter V-8 engine with automatic cylinder deactivation. This amenity was the subject of Dusan Gruden’s research and, in fact, had been licensed to Ford of Europe for use in its V-6 engines.
The alternative was a 2.25-liter, four-cylinder powerplant based on the cylinder dimensions of the original 928 V-8. While that had single overhead cams, the 995 could have the luxury of a 16-valve cylinder head. Such a powerplant in V-8 form would power the 928 a decade later. For the present, the four-cylinder would bring its advantage of greater lightness to the 995 concept.
Comparison of several transmission variants, including a hydrodynamic torque converter, showed that the automatic mechanical five-speed PDK transmission with double-clutch action was the most favorable solution. The complete unit was to be mounted forward of the final-drive ring and pinion, the latter taking drive from the lower shaft of the transmission. The upper shaft accepted the drive from the forward powerplant into the PDK’s pair of input clutches. Thanks to racing experimentation the transmission was electronically controlled without letting up on the gas pedal, which contributed to the high efficiency of the drive system.
Among the 995’s planned amenities was a central electronic system to be installed for ignition, fuel injection, and transmission control, as well as other duties such as a central information system. Its mission was to operate the power train in its range of maximum efficiency. In addition to a comprehensive package of passive safety measures, an optimized anti-lock brake system enhanced active driving safety.
A special challenge to Project 995 was its shape. This had to be a car with exceptionally low aerodynamic drag. Although its fundamental shape was derived from the 928, its form was extended and refined, especially around its frontal configuration and its extended tail. From model testing the result was a commendable drag figure of Cd=0.30. Complementing its form was the decision to specify aluminum for its coachwork.
Fuel-economy strategies included reduced vehicle weight and low aerodynamic drag, minimization of parasitic losses (e.g., by low-friction drive shafts), improved energy-efficiency measures, and smoother power transmission. Its calculated fuel consumption came in under 26 miles per gallon.
Although the Porsche’s 995 project never evolved into a production model, it provided:
• Research that appeared later in the Porsche 959 (Group B, mid-1980s)—especially in its aerodynamic shaping, use of composite materials, and energy-efficiency focus.
• Broader knowledge shared within the Volkswagen Group as part of the BMFT program’s findings.
• In some sense, the Type 995 marked Porsche’s first systematic exploration of “sustainability-oriented performance”, a theme that echoes today in its electric and hybrid models.
Porsche, then known primarily for its high-performance sports cars, used the BMFT opportunity to broaden its research portfolio into light-weight, aerodynamically efficient vehicle design. Its designers’ use of light-weight alloys and composite materials opened a way for engineers to experiment with energy-efficient sports-car concepts without the pressure of immediate market release. It served as a test bed for low-weight, low-drag design principles that would later influence models like the 944 and 959. Not bad for a non-runner.
