I got sick of looking at the 30 scanned copies of the leaked 2008 Porsche 911 GT2 brochure this morning, so I had my secretary transcribe the entire thing for me. Don’t thank me, thank her! 
At Porsche, our aim is not to increase power – except through increased efficiency. This is why we began with the 911 Turbo when developing an engine for the new 911 GT2. Its power is combined with rear-wheel drive for racing-car driving dynamics.
But how is it possible to improve on an engine that is already so close to perfection? How did we introduce even greater potential – ant the character of a racing engine? The answer: BY SIMPLY INCREASING EFFICIENCY.
The six-cylinder boxer unit has flow-optimized turbines featuring Variable Turbine Geometry (VTG) and larger compressors on the intake side. Together with VarioCam Plus, they boost performance while reducing emissions over the entire engine speed range. Other important features include the revolutionary new expansion intake manifold and the new titanium main silencer.
The results: 530hp from a 3.6 liter displacement at 6500rpm. Maximum torque of 505 lb-ft is available from 2200 to 4500rpm. The benchmark sprint 0-60mpg is complete in 3.6 seconds; 0-100mph requires just 7.4 seconds and top track speed is 204mph.
Variable Turbine Geometry (VTG)
Porsche has a long and celebrated tradition of using turbocharged power on both road and track. On the new 911 GT2 we’ve enhanced this technology with VTG.
On a conventional turbocharger, the exhaust flow drives a turbine that is connected to a compressor on the intake side. By compressing the incoming air, the amount of oxygen in a given volume is increased. Since compression also causes an increase in temperature, the air must be cooled in a device known as a “intercooler”. With more oxygen present in each cylinder charge, more fuel can be burnt yielding greater energy. Since higher exhaust pressures generate greater loads on the intake side, the intake pressure must be carefully controlled in order to protect the engine. On the new 911 GT2 this ‘boost pressure’ is limited using ‘waste gate’ valves that bypass excess pressure around the twin exhaust turbines.
Another important factor in the system is the size of the turbochargers. Since a smaller turbine has a lower mass, it responds more quickly to increasing pressure, spinning up easily to its optimum speed. The key disadvantage of using a smaller turbo is that the back-pressure generated at higher engine speeds causes a significant reduction in performance. Resistance is caused by the smaller cross-sectional area through which the exhaust is required to flow. Larger turbo units, which create lower back-pressure at higher rpm, take considerably longer to spin up under power due to the large cross-sectional area and relative inertia of the heavier turbine. Generally, this type of turbo will only be effective in the medium rpm range. This phenomenon, known as ‘turbo lat’, means there is virtually no turbo charging effect at lower engine speeds.
To overcome this problem, the twin water-cooled turbochargers on the new 911 GT2 feature VTG. With this technology, the gas-flow from the engine is channeled onto the turbines via electronically adjustable guide vanes, by changing the vane angle, the system can replicate the geometry in all types of turbo, large or small, and thus achieve the optimum gas-flow characteristics. The guide vanes are controlled by the engine management system. The result is a high turbine speed – therefore higher boost pressure – even at low engine rpm. With more air available, the combustion is increased, yielding greater power and torque.
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