November 16, 2005
Big Anniversary on 16 November
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 Porsche Turbo – 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".
(Nov. 15, 2005)