The words “Porsche” and “turbo” have been synonymous with ultimate high performance since 1972, when the automaker first used boosted engines in the mighty 917/10 Can-Am racecars. For 2016MY, the company is introducing all-new turbocharged 3.0-L flat-six engines for the 911 Carrera and Carrera S road cars, replacing naturally aspirated (NA) 3.4-L and 3.8-L units. The 911 that carries the specific "Turbo" designation, however, will continue to use a 3.8-L engine.
The 3.0-L Carreras will be unveiled at the 2015 Frankfurt Motor Show. The downsized-and-boosted "boxer" brings new levels of efficiency and added power; the Carrera gets an extra 15 kW (20 hp) taking peak output to 272 kW (365 hp). The Carrera S produces 309 kW (414 hp), also a 15-kW improvement. The new engines use two BorgWarner turbos, one per cylinder bank.
The S version of the 3.0 L features modified turbine compressors, a specific exhaust system and tuned engine management. Boost pressure is 0.9 bar (13 psi) in the Carrera and 1.1 bar (16 psi) in the Carrera S. The new engine also produces more peak torque – an added 60 N·m (44 lb·ft), delivered from 1700 to 5000 rpm, to provide 450 N·m and 500 N·m (331 and 368 lb·ft), respectively. Both variants are rev-limited to 7500 rpm.
Performance of both the Carrera and Carrera S is slightly improved, the S fitted with PDK (dual clutch) and Sport Chrono Package achieving a claimed 0-100 km/h in 3.9 s, and top speed of 307 km/h (190 mph). But fuel consumption and emissions are markedly better; the S with PDK achieves a combined figure of 7.7 L/100 km, an improvement of 1.0 L/100 km. Claimed CO2 emissions are 169 g/km for the regular Carrera, 174 g/km for the Carrera S.
According to Porsche technology spokesperson Nick Perry, the new 911 models will not be badged “Turbo.” He also explained that the very high performance 911 GT variants were a “separate topic” with regard to the application of turbocharging: “The current Turbo will continue to be described as that; the model offers a different image and attributes to those of the Carrera. We have turbochargers in the Panamera, Cayenne and Macan, but there, too, we use the designation Turbo for top of the range versions.”
Inside the new boxer
Track-to-road technology transfer is a major element of Porsche’s engineering creed but its racing 911s have NA engines to meet regulations. “The NA GTRS 4.0-L engine will continue to power our 911s in the motorsport realm," Perry explained. "But for road cars there is a multitude of criteria to meet, which is why we are introducing the new engine."
He described the new engine as a "step-change"—the 3.0-L being all-new and not a derivative of the 3.4 and 3.8 engines. The move is similar to when Porsche went to liquid cooling (1998MY) to reduce drive-by noise, improve performance and efficiency, running the engines hotter and achieving better combustion. Another step-change came in 2008 with the introduction of direct fuel injection.
Porsche is making no formal comment about the new 3.0-L turbo family forming the basis of engines for other models ranges including the Boxster and Cayman, but siblings can be expected.
The use of forced induction has required a new engine airflow system for combustion and intercooling at the rear of the Carreras. The engine gets its combustion air centrally in front of the rear spoiler. From two lateral ports on the air filter box, the airflow reaches two induction channels to the lower-mounted turbochargers. The compressed and heated air then flows through two intercoolers located laterally behind the wheel arches and onwards to the engine's induction manifold via the throttle plate. Two other ducts guide the air for cooling the heated combustion air (also from the air screen in the rear lid) to the intercoolers.
The 3.0-L’s injectors are located in the center of the combustion chamber for greater combustion efficiency. They are fed by two fuel pumps, one per cylinder bank, operating on a system pressure of up to 250 bar (3626 psi). Variable exhaust-camshaft timing facilitates precise control of the charge exchange process. On the intake side, Porsche continues to use VarioCam Plus, adjusting both valve lift and opening duration.
A new cylinder wall coating process, in which a plasma beam coats the bore surface with iron, helps reduce friction losses, according to Porsche engineers. And extensive FEA analysis during the design process helped cut the weight of the aluminum crankcase by 1.5 kg (3.3 lb). A new engineered-plastic oil pan is 2 kg (4.4 lb) lighter than in the previous generation engines.
The water pump now has a clutch that is controlled by thermal management and can remain disengaged at low coolant temperatures. The deactivated pump no longer draws any engine power, and the coolant just circulates slowly. Friction is reduced and the engine reaches its operating temperature more quickly. The same applies to the air conditioning compressor; it can also be completely deactivated via a clutch.
Transmission developments include introduction of a two-disc clutch for the new engines for comfortable operation despite the new 3.0-L’s high torque. And the PDK has new operating logic. As in the 911 GT3 and many Porsche racecars, pulling the selector lever back now provides upshifting; pressing it forward triggers downshifting. Porsche is now using a dual-mass flywheel with a centrifugal pendulum in conjunction with the PDK, as well as intelligent overrun cut-off and "virtual" gears.
The centrifugal pendulum is also used with the manual transmission. It has an adaptive vibration absorber that dampens vibrations in the drivetrain over a broad range of engine speeds, according to Porsche engineers.
In combination with the Sport Chrono and PDK systems, the 911 driver now has a “mode switch” which has an additional “sport response” button which activates a pre-conditioned drivetrain response which provides maximum acceleration for 20 s, the optimum gear engaged and engine management adjusted for optimum spontaneous response such as for overtaking.
Active rear-axle steering and suspension
Complementing the new powertrain developments, chassis changes for the 911 include active rear axle steering as an option for the Carrera S, The technology is adapted from the 911 Turbo and the 911 GT3 as well as the exotic limited-production 918 Spyder.
The active rear axle is designed to enhance the turn-in behavior of the 911 and reduces the car’s turning circle by 0.5 m (1.6 ft). Porsche is offering a 360-mm-diameter (14-in) steering wheel that is 15-mm (0.6-in) smaller than the previous wheel.
Porsche Active Suspension Management (PASM) is fitted to all Carreras for 2016. It lowers ride height by 10 mm (0.4 in). An optional hydraulic lift system increases the car’s ground clearance by 40 mm (1.6 in) via lifting cylinders in the front suspension struts to clear steep garage ramps and speed bumps.
Porsche states that introducing turbocharging for the Carreras was a logical next step in a technology path that began four decades ago. The original Turbo engine of 1974 had a claimed power output of 194 kW (260 hp) and consumed 20.9 L of high-octane gasoline per 100 km. By comparison, the new-for-2016 flat six-cylinder engine produces 42% more power with more than twice the fuel economy, while using the same cylinder displacement. Progress all around!Continue reading »