The exhaust gas turbocharger was invented 100 years ago tomorrow, by Dr. Alfred Büchi. Porsche is using this anniversary to introduce its new variable turbine geometry for gasoline engines on the all-new 911 Turbo (see recent spy shots). The technology has long been used on diesels, but never in regular gasoline applications. The core features of the VTG system 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.
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.
Big Anniversary on 16 November
On November 16th, 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.
