- Nov 13, 2007
2008 Porsche 911 GT2 introduction: Engine technology
Porsche's latest turbocharged engines are a far cry from the automaker's forced-induction offerings from two decades ago. Modern engine management systems tamed the lightswitch-like power delivery, and now the use of variable camshaft phasing and variable-vane turbocharger technology has resulted in a powerband that's flatter and fatter than that of larger naturally-aspirated motors.
The GT2 uses a pair of BorgWarner/KKK turbochargers that are similar to those employed on the Turbo, but with a slightly larger compressor and some flow optimization applied to the turbine side. Additionally, the ECU allows a bit more boost, and the result is an astonishing 505 lb-ft from 2200 to 4500 RPM. Even after the peak is reached, plenty of thrust remains through the next 2000 RPM up to the horsepower peak of 530 at 6500 RPM. To the driver, this means that enormous power is on tap basically anywhere between idle and redline. Gear selection can be treated as an afterthought with minimum penalty, which is a useful attribute when there are several other decisions to be made on the racetrack or street.
Visible in the shot above is the tangle of oil lines that's required to operate the variable vanes on the turbo's turbine side. Expect future generations of this technology to utilize direct-mounted electrical actuators, but temperature in this area remains troublesome - as it is, miraculously tight tolerances and careful management of thermal expansion is required to make VVT technology work with the hotter exhaust temps of spark-ignition engines.
The management of induction tract resonances is critical to maximizing the power of naturally-aspirated engines, but the turbocharged engines have typically foregone this technique in favor of adding additional manifold pressure (resonances in a pressurized manifold are also extremely tricky to tame). Cranking up the boost has a drawback, however, in the form of additional heat, and so more fuel and less timing is required to maintain acceptable durability.
Porsche claims to have countered this with an "expansion-type" manifold that makes use of the typically-unused oscillations that are still present in a forced-induction manifold. A longer and smaller-diameter primary tract is combined with more plenum volume and shorter individual cylinder runners to yield a cooler intake charge for a given flow rate, which means that the fuel mixture can be leaned and more ignition timing can be utilized. Both changes improve fuel economy and dump less heat into the exhaust system - undoubtedly a win-win scenario. Amazingly enough, it all fits in the restrictive rear engine compartment of the 911, and we expect to see this on future forced-induction engines from Porsche.
The use of titanium components for the exhaust system frees up several pounds, and while Porsche doesn't credit it with any improvement in power, we like it just for the enhanced sonic qualities. For those viewing the tail end of the GT2 - that'd be most observers - a set of polished tips poke through the rear valance.
Routing all 530 HP to the six-speed transaxle requires a heavy-duty clutch, but balancing torque transmission with pedal effort and durability requires some fancy engineering. Additionally, it's desirable to keep mass and diameter to a minimum to avoid creating too much inertia (ground clearance also becomes an issue with low-riding sports cars). A twin-disc clutch from Sachs is used here; doubling the number of discs increases the torque capacity accordingly without an increase in pressure plate force. The GT2's clutch pedal is still heavier than most, but it's manageable. We'd still recommend some time at the gym before getting stuck in rush-hour traffic.