The full range of movement of the turbine blades takes merely 100 milliseconds and is controlled · by the engine's Motronic® elect

The full range of movement of the turbine blades takes merely 100 milliseconds and is controlled by the engine's Motronic® electronic control module (ECM). Action of the variable turbo vanes is so precise that there's no need for a turbocharger bypass valve to limit maximum boost. To reduce excess boost pressure on the throttle butterfly when the driver quickly lifts off the throttle or in overrun, the Turbo features an automatic bypass valve which saves space via a new placement on the compressor housing. The intake charge from each of the engine's two turbochargers is cooled by a dedicated intercooler, each located ahead of a rear wheel, as has been a Porsche Turbo hallmark. The result of this sophisticated engineering and complex manufacturing is a turbocharged engine that responds to the driver's demand for more power immediately. There is no time lag between stepping on the throttle and the expected rush forward of boost. In fact, the VTG delivers its rewarding surge of power as quickly as an engine with a mechanically driven supercharger, but without the penalty of the supercharger's parasitic power drain on the engine. More for those who want it To ensure the expected high level of engine response and long life, maximum intake pressure is set to approximately 14.5 psi, or 1 bar. The optional Overboost feature briefly allows approximately ten-second bursts of 17.4 psi or 1.2 bar, at the touch of a console-mounted button. On-the-road tests show that with Overboost, 50 to 75 mph (80 to 120 kmph) passing time— without downshifting from second highest gear—is just 3.6 seconds, vs. 3.9 seconds without the use of Overboost. Porsche engineers measure boost levels at sea level, under full load and at an ambient temperature of 68°F (20°C). Keeping it cool Though the VTG concept has been applied to Diesel engines for some time, it has not been commonly used with gasoline engines due to the higher heat of gasoline exhaust. Diesel exhaust temperatures are much cooler than gasoline engine exhaust, which places far less thermal stress on the turbocharger's components. Diesel exhausts are approximately 1250°F (700°C), compared with gasoline engine exhaust temperature of about 1850°F (1000°C). In order to allow the turbine blades to adjust, rather than be fixed, Porsche's engineers had to tame the demon heat by rethinking turbocharger design and materials. To ensure both high performance and a long, trouble-free service life, the turbo designers created turbochargers with adjustable turbine vanes and double redundancy cooling. In addition to the existing oil cooling for the turbo bearings, the turbos also have a water cooling system and a follow-up pump to keep the bearings temperatures under control. Regardless of turbo design, all turbocharged engines are subject to more stress than their naturally aspirated equivalents.