November 18, 2005 The turbo-charger , which has dominated the development of the internal combustion engine for the last 30 years, turned 100 years old this week. On 16 November 1905 Swiss engineer Dr. Alfred Büchi received patent No. 204630 from the Imperial Patent Office of the German Reich for a "combustion machine consisting of a compressor (turbine compressor), a piston engine, and a turbine in sequential arrangement". Porsche chose the occassion to introduce its very latest take on the turbocharger, this time with variable turbine geometry (VTG). This extensive article covers the development and major achievements of the turbocharger and the new VTG technology which realises even more efficiency, resulting in a significant improvement of engine flexibility and acceleration particularly at low engine speeds. In introducing the new 911 model some 31 years after it gave us the first series production sports car with an exhaust gas turbocharger (the 1974 Porsche 911 Turbo), Porsche will be presenting the world's first turbocharged gasoline engine with variable turbine geometry (VTG).
This technology featured in turbocharged diesels since the '90s ensures a significant improvement of engine flexibility and acceleration particularly at low engine speeds. So far, however, much higher exhaust gas temperature of up to 1000° C in comparison with the turbocharged diesel has always proved to be an insurmountable barrier. But now Porsche has solved this problem in close cooperation with Borg Warner Turbo Systems by using high temperature-resistant materials from space technology wherever required.
The very concept of turbocharger technology is linked inseparably with the name Porsche and the Porsche brand. It was back in October 1974 that the German sports car manufacturer from Stuttgart launched the world's first series production sports car with an exhaust gas turbocharger. And ever since, each new generation of the Porsche 911 Turbo has fascinated enthusiasts the world over with a new and distinctly better enhancement of the technology: the intercooler, bi-turbo, VarioCam Plus, as well as the title "Cleanest Car in the World" have all set the benchmark in turbocharger development. Now the new competitive edge of the next generation of the Porsche Turbo is spelt VTG - variable turbine geometry.
The core features of VTG are the variable turbine blades guiding the flow of exhaust gas from the engine in exactly the direction required on to the turbine wheel of the exhaust gas turbocharger. The principle of variable turbine geometry thus combines the benefits of a small and large exhaust gas turbocharger all in one – a combination ensuring both very good response and high torque at low engine speeds as well as superior output and high performance at high speeds. And the supreme level of torque is now maintained consistently throughout a much wider speed range.
Happy Birthday The exhaust gas turbocharger was invented exactly 100 years ago: On 16 November 1905 Swiss engineer Dr. Alfred Büchi received patent No. 204630 from the Imperial Patent Office of the German Reich for a "combustion machine consisting of a compressor (turbine compressor), a piston engine, and a turbine in sequential arrangement".
Born on 11 July 1879, Büchi, who died on 27 October 1959, worked as an engineer in the Swiss town of Winterthur. His idea was not just to pre-compress the air flowing into the engine, but also to use the kinetic energy coming out in the exhaust gas under high pressure, which otherwise was simply wasted. So he used the exhaust gas flowing out after the combustion process to drive a turbine serving, in turn, to drive a compressor pre-compressing the intake air and boosting the air charge in the engine. This marked the birth of the turbocharger.
Büchi had to wait a long time until his invention was able to enter practical use. The first application of turbocharger technology was in large marine engines, with the German Ministry of Transport commissioning the construction of the "Danzig" and "Preussen" passenger liners in 1923. Each of these two passenger ships had twin ten-cylinder diesel engines with output boosted by turbocharger technology from 1750 to 2500 horsepower.
The first attempts to use this technology in the automobile began in the late '50s, with the so-called "turbo gap" – the delayed response of the engine to the throttle – presenting development engineers with a challenge still insurmountable at the time.
In 1973 Porsche raced the 917/30 developing more than 1100 bhp as a spearhead in turbocharger technology in the US CanAM Series, this ultra-powerful racing car literally destroying its opponents on the track. The result was a modification of regulations in the CanAM Series sending the almighty 917/30 straight to the museum.
First 911 with Turbocharger Technology
Maximum output of 260 horsepower, top speed of 250 km/h (155 mph) plus, acceleration to 100 km/h in 5.5 seconds – boasting supreme performance figures of this calibre, the first Porsche 911 Turbo made a proud appearance at the Paris Motor Show in 1974. This supersports developed its peak output at a low 5500 rpm, with torque peaking at 343 Newton-metres or 253 lb-ft at 4000 rpm. Back then this kind of torque achieved by Porsche was absolutely unheard of in a turbocharged power unit. Porsche's engineers were able to give the engine this relatively harmonious flow of power through the skilful use of a bypass valve. And to reduce the "turbo gap", Porsche's development engineers used a small turbocharger responding at an early point in time and reducing the lack of torque accordingly.
Entering the market in 1977, the successor to the original Turbo developed an even more significant 300 horsepower from 3.3 litres. The increase in output was achieved at the time by a brand-new feature, an intercooler seen for the first time on a production car. Cooling the hot turbocharger air to less than 100°C, the intercooler was able to reduce turbocharger pressure without the engine losing any of its power.
The eighties saw the turbo-charged era of motor racing which culminated in the most comprehensive domination of a Formula 1 season by any car before or since – the McLaren Honda Formula One team won 15 of 16 races, lead 1003 of the 1031 laps in the season, take 15 of the 16 pole positions and see the two MP4/4s finish one-two ten times from 16 starts. The Honda-powered McLaren MP4/4 dominated the 1988 season partially due to the extraordinary quinella of drivers, (the late Ayrton Senna and Alain Prost) but mainly due to its 800 horsepower 1.5 litre turbocharged engine.
Turbocharging was banned in 1989 and where other manufacturers stopped development of turbo engines when the ban and 1988 fuel consumption penalities were announced, Honda developed a miserly horsepower machine which trounced the competitors. Indeed, had it not been for a remarkable incident where Ayrton Senna was comfortably leading the Italian Grand Prix at Monza and crashed into a driver he was lapping, the car would have won every race of the season.
A Clean Performer in Every Respect In 1990 Porsche enlarged the top segment through the introduction of a new 911 Turbo. An intercooler now 50 per cent larger, a turbocharger also increased in size, and pressure-controlled mapped ignition served to boost maximum output to 320 horsepower. And at the same time the new car was also a very clean performer, advanced exhaust gas management featuring a fully controlled three-way catalytic converter in metal substrate technology fulfilling the strictest US emission standards. Even the emissions coming out through the bypass valve were cleaned by means of a separate catalyst.
The fourth-generation 911 Turbo made its appearance in early 1995, based on the 3.6-litre power unit carried over from the 911 Carrera. The engine's performance figures, however, now entered a new dimension, with the new power unit featuring a twin turbocharger. So following the Porsche 959 technology spearhead boasting a second exhaust gas turbocharger for the first time in 1987, bi-turbocharger technology now made its way successfully into series production.
Maximum output of the new 911 Turbo was a shattering 408 bhp at 5750 rpm, with peak torque of 540 Newton-metres or 398 lb-ft at 4500 revs. Clearly, this ensured truly sensational performance, the Turbo accelerating to 100 km/h in 4.5 seconds and continuing on consistently all the way to a top speed of 290 km/h or 180 mph. Once again, the entire process of developing power was even more harmonious, the two smaller turbines responding even more quickly to the flow of exhaust gas.
Another masterpiece achieved by Porsche's engineers was the car's exhaust management system, sophisticated catalyst technology in conjunction with Porsche's new On-Board Diagnosis II (OBD II) making the new 911 Turbo the cleanest car in the world. Using the engine's electronic "brain", OBD II was able to detect possible deficiencies in the management of exhaust emissions and record up to 20 malfunctions for subsequent diagnosis.
Two Engine Concepts in One
The most outstanding technical highlight featured in the current 911 Turbo which entered the market in early 2000 is VarioCam Plus, an ingenious system reducing both fuel consumption and emissions and improving the engine's refinement at the same time. A further benefit of this superior technology is that it optimises both engine output and torque, the Turbo now developing 420 bhp at 6000 rpm and reaching a top speed of 305 km/h or 189 mph. Fuel consumption, in turn, is 18 per cent lower than on the former model.
The great advantage of VarioCam Plus is that it combines two engine concepts in one, adjusting the camshaft on the intake side and varying the engine's valve stroke by means of Motronic engine management. This means even greater fuel economy and lower emissions both when idling and under part load, combined with high torque and maximum output at full load ensured by uncompromising cam contours with valve stroke of not more than 10 millimetres or 0.39".