Automotive Intelligence - the web for automotive professionals and car enthusiasts
October 2, 2002
The new Eco-Speedster is proof of the progress made in the last 30 years and of the diesel engine's amazing passenger-car career. When the record-breaking GT made its sensational appearance, it was the first time that "sports-car performance" had been associated with the diesel engine. The performance of the very compact unit in the new engineering study is particularly impressive. The all-new ECOTEC-CDTI diesel, with the latest multi-jet common rail fuel injection, four valves per cylinder and variable-geometry turbocharger, has a displacement of only 1.3 liters.
Powerful, Compact and Clean: The World's Smallest Four-Cylinder Diesel
This innovative engine is notable for its compact dimensions (length/width/height: 460/500/650 millimeters). In terms of fuel consumption, emissions and refinement it proves to be one of the best diesels of all. Compared with other current engines of similar output, fuel consumption will be down by approx. 10 percent and emissions will be cut by 30 to 40 percent and thus outperform the Euro 4 limits. At 1251 cc, this ECOTEC unit is the world's smallest four-cylinder diesel, but with regard to output and torque it can compete with substantially larger engines.
The basis for this performance potential is the ultramodern design of the new 1.3 CDTI ECOTEC engine. An alloy cylinder head tops the weight-optimized cast-iron engine block (bore x stroke 69.6 x 82.0 millimeters). There are four valves per cylinder, operated by roller cam followers from two chain-driven overhead camshafts. The latest multi-jet direct injection system with fuel supply by 'common rail' at a pressure of 1600 bar is another noteworthy feature.
Fuel supply to the five-hole nozzles is controlled via an ultramodern solenoid valve. The fuel injection system's response time is less than 20 millionths of a second, ensuring extremely fine metering of the fuel and up to five injections per working cycle. This not only keeps fuel consumption and exhaust emissions extremely low, but also ensures smooth, low-noise operation. Pilot injection helps to reduce the once notorious diesel-engine knock in the warm-up phase to a hardly identifiable level.
Slim, Long and Flat: an Extremely Aerodynamic Body
Whereas the diesel engine is of completely new design, the advanced engineering team at Opel's International Technical Development Center (ITEZ) was able to make use of a tried-and-tested basis for the car itself. "The Speedster was nevertheless subjected to some fundamental modifications," explains Walter Treser, head of Opel's Advance Engineering department. "In order to achieve our own target of over 250 km/h top speed and a standard test consumption of only 2.5 liters per 100 kilometers, considerable improvements in aerodynamics and weight were essential." By facing this challenge, the engineers had an opportunity to demonstrate the limits of feasibility in this area.
Calculations soon showed that the target performance figures could only be achieved by reducing the drag coefficient by half - definitely a highly ambitious goal. And in due course it became clear: This target could not be achieved by pure optimization - more radical steps would have to be introduced.
The first step was to reduce the Speedster's frontal area. The design engineers lowered the now rigid roof of this already low-slung sports car by another 167 millimeters and gave the car a more steeply raked windshield. The result: The Eco-Speedster's height is a mere 950 millimeters, which would make it almost impossible to enter and leave through standard doors. The design study was therefore fitted with gullwing doors. An extremely small detachable steering wheel also helps to make entering the car more convenient and gives the driver more room. The backs of the carbon-fiber reinforced racing seats were also given a more inclined position. Since occupant comfort was not yet one of the main priorities, the cockpit was also reduced in width above the waistline. The result: A frontal area, in technology identified with the letter A, of only 1.4 m2 - 12.5 percent less than the production Speedster.
On this basis and according to the motto "length means speed", the next task was reducing the drag coefficient. The most striking novelty is the long tail. It extends 184 millimeters farther back, so that the airflow clings closer to the body and generates less turbulence. The impression of extra length is enhanced by the panels above the mid-engine; looking at the car from the side, there is a continuous gently sloping line from the windshield frame to the tail panel. Further visual clues to the excellent aerodynamics are the almost complete paneling of the rear wheel cutouts and the smooth front wheel covers. In wind tunnel tests, final detailing led to the results calculated by the design computer in advance: With a cD of 0.20 and an overall aerodynamic drag (cD x A) of 0.28 m2, the Eco-Speedster slides 47 percent more easily through the air than its production counterpart.
Classical, Clear, Modern: a Design Study Typical of Opel
Stefan Arndt, designer of the Eco-Speedster, is not only happy about the technical results obtained by the modifications: "With its long tail and the pronounced cockpit dome including the gull-wing doors, the design study reminds me of the classic long-distance cars of the 1960s. We succeeded in maintaining the characteristic edges of the Speedster as well as typical elements such as headlamps and tail lights and the trapezoidal front-end styling. The Eco-Speedster is not in the least nostalgic, however: it looks like an Opel and is recognized as one at first glance."
In order to realize the so far unique combination of exemplary moderate consumption and sporty performance, according to the formula 2.5 x 250, the engineers had to go the limits as far as weight saving and rolling resistance were concerned. What can't be seen under the elegant light-silver competition-car finish, but shows up on the scales: all elements of the body's outer skin are made of carbon fiber. Based on the Speedster's light, rigid aluminum frame, the weight of the prototype has been reduced to 660 kg. Further factors such as particularly low-resistance size 175/55 R 17 W tires and special low-friction engine oil complete the Eco package for the Speedster.
Explaining the prototype's background, Opel's Chief Executive Officer Carl-Peter Forster says: "The Eco-Speedster symbolizes our comprehensive diesel offensive and at the same time demonstrates Opel's engineering expertise in power trains, weight-saving design and aerodynamics. By the end of 2003 we will have introduced four new, state-of-the-art common rail diesel engines with a wide range of power outputs, low weight and moderate fuel consumption."
(September 26, 2002)