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New Porsche 911 Turbo
1st VTG for a gasoline engine

VTG turbocharger with low blade angle at low engine speeds.

VTG turbocharger with a steep blade angle at high engine speeds

VTG turbocharger: low blade angle at low engine speeds (top) and with a steep blade angle at high engine speeds (bottom).

APN,
6th March 2006.

Back in October 1974, Porsche launched the world's first series production sports car with an exhaust gas turbocharger. Ever since, every new generation of the Porsche 911 Turbo brought a special highlight in technology: the intercooler, bi-turbo, VarioCam Plus...

Now is turn of the new generation 911 Turbo to bring its new height: variable turbine geometry (VTG).

With the new 911 Turbo, Porsche will be launching in June the world's first turbocharged gasoline engine with variable turbine geometry (VTG).

Since the '90s, this technology has been known in improving turbocharged diesel engines flexibility and acceleration, particularly at low engine speeds.

So far, however, much higher exhaust gas temperature in gasoline engines (up to 1000° C) in comparison with the turbocharged diesel has always proved to be an insurmountable barrier.

VTG turbocharger with low blade angle at low engine speeds - blades

VTG turbocharger with a steep blade angle at high engine speeds - Blades

VTG turbocharger: low blade angle at low engine speeds (top) and with a steep blade angle at high engine speeds (bottom).

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 core features of the VTG system are the variable turbine blades (opposite photos) 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.

A century of turbocharging - The exhaust gas turbocharger was invented over a 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 (which is the direct charging principle), 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 lag" or "turbo gap" – the delayed response of the engine to the throttle, expressed in a sudden surge in power as soon as the turbo starts to intervene – presenting development engineers with a challenge still insurmountable at the time.

The Porsche 917/30 won the CanAM Series in 1973, developing more than 1100 bhp

In 1973 Porsche raced the 917/30 developing more than 1100 bhp.

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.

911 Turbo - The first Porsche 911 Turbo made its appearance at the Paris Motor Show in 1974, boasting a maximum output of 260 horsepower, top speed of 250 km/h (155 mph) plus an acceleration to 100 km/h in 5.5 seconds.

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" (known also as turbo lag), 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 1990 Porsche 911 Turbo came with a intercooler 50 per cent larger than the previous one, a turbocharger also increased in size, and pressure-controlled mapped ignition served to boost maximum output to 320 horsepower. That new car was also a very clean performer, with 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.

1995 - 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 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 408 bhp at 5750 rpm, with peak torque of 540 Newton-metres or 398 lb-ft at 4500 revs, 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. Power delivery was even more harmonious, the two smaller turbines responding even more quickly to the flow of exhaust gas.

Another achievement 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.

Previous 911 Turbo entered the market in 2000 with the VarioCam Plus.

the previous 911 Turbo came in 2000 with the VarioCam Plus.

2000 - The most important technical highlight featured in the following 911 Turbo which entered the market in early 2000 was the VarioCam Plus system, reducing both fuel consumption and emissions and improving the engine's refinement at the same time. A further benefit of this 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".

2006 Porsche 911 Turbo: output rises to 480 bhp with better flexibility.

2006 - With the sixth generation 911 Turbo (Type 997), using special materials extremely resistant to high temperatures, Porsche's engineers have succeeded in developing an exhaust gas turbocharger with variable turbine geometry (VTG) able to withstand very high exhaust gas temperatures of up to 1000° C or 1830° F also on a gasoline engine. So now one turbocharger with variable turbine geometry offers the advantages of both a small and a large turbocharger all in one. Output rises to 353 kW (480 bhp) at 6,000 revolutions per minute, 60 bhp more than the 2000 911 Turbo (Type 996), with a much improved flexibility. The specific output of the 3.6-litre boxer engine thus climbs to a 98 kW (133 bhp) per litter of displacement.

Even more significantly, while the previous 911 Turbo's maximum torque (560 Newton-metre) was available between 2,700 and 4,600 rpm, the corresponding figures are now 620 Newton-metres at 1,950 to 5,000 revs.

In terms of driving performance, the new 911 Turbo with six-speed manual transmission requires 3.9 seconds for the standard sprint from zero to 100 km/h, before crossing the 200 km/h mark in 12.8 seconds, with just 3.8 seconds to accelerate from 80 to 120 km/h in fifth gear.

Despite the enhanced performance, Porsche reduced average fuel consumption by one tenth to 12.8 litres per 100 kilometres.

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