Instead of the traditional manifold pressure-referenced mechanical actuators, electric stepper motors are used to precisely control wastegate position for improved boost response and control. These new turbochargers also feature Porsche’s first use of electric controls for the internal wastegate valves. All previous twin-turbocharged Porsche engines used turbochargers with compressor wheels that both rotated in the conventional clockwise direction the 992 features symmetrical turbochargers that rotate in the opposite direction of one another to fully equalize exhaust particle flow between the two exhaust manifolds. Replacing the air-gap insulated sheet metal manifolds of the 991.2 are cast-iron manifolds which are designed to be lightweight while retaining heat energy that is transferred to the turbine housings of the turbochargers. The exhaust manifolds and turbochargers of the 992 were also refined. This configuration allows 14 percent larger intercoolers and shortens the air intake air path by 50 percent for better throttle response. The adoption of the wide-body format across the 992 Carrera range (previously reserved for all-wheel-drive Carrera 4S models) allowed the intake configuration to be reversed the intercoolers are now positioned atop the engine, with the fresh air intakes at the sides. The integration of turbochargers and intercoolers within the confines of the wingless, narrow-bodied 991.2 platform required clever space engineering on the part of the Porsche engineering staff. This worked well for Porsche’s gasoline DFI engines for over ten years, but the mass and inertia of the injector pintles and the heavy return springs required to hold the pintles closed against increasingly high fuel rail pressures ultimately limited the scope of precision of the solenoid injectors. A solenoid injector uses an electromagnet to lift the injector pintle when voltage is applied, which enables fuel to exit the injector. Long a mainstay in the world of common-rail diesel engines, piezo injectors enable much more precise control of the injected fuel versus the previous solenoid-style injectors. The “high” lift setting is the same for all intake valves.įurther improving efficiency is Porsche’s first use of piezo-electric fuel injectors in a gasoline direct fuel injection ( DFI see the #223/November 2014 tech feature for more info) engine. Smaller valve lift at low engine speeds also results in less overlap of the intake and exhaust valve openings during these conditions, which raises the dynamic compression ratio to improve cylinder filling and thus enhance off-boost engine response. But while that engine employed this strategy to prevent consecutive exhaust pulses from interfering with each other, the 992 engine’s use of 2.0-millimeter (0.08 in.) and 4.5-mm (0.18 in.) small lift values to promote a swirling effect within the cylinder and thus enable a more homogeneous air/fuel mixture. This asymmetric valve lift concept has previously been used on the first-generation (9PA) Cayenne S V8 engine of 2003. The static compression ratio is raised from 10.0:1 to 10.2:1, and combustion efficiency is improved by using different “small” valve lift amounts on the adjacent intake valves of each cylinder. Porsche engineers accomplished this feat by refining many details of the engine and its ancillaries. The 379-hp 992 Carrera and 443-hp Carrera S engines produce respective gains of 9 hp and 23 hp, while also improving fuel efficiency. The “9A2 Evo” engine of the 992 uses the same basic aluminum block structure as the 991.2 with identical bore and stroke dimensions (for a 3.0-liter displacement in both base Carrera and Carrera S engines), along with iron-coated cylinder liners via plasma wire transfer arc technology ( PWTA, see the April 2017/#244 tech feature about the 991.2 engine for more info).
NEW PORSCHE 911 ENGINE SKIN
While the 992 seems to be more of an evolutionary redesign, some of the details under its skin represent a revolution in terms of its construction and its electronic subsystems, along with Porsche’s adaptation of corporate VW/Audi group body architecture and production processes. The 2020 992 represents the eighth distinct generation of the Porsche 911, and it continues the company’s alternating pattern of a revolutionary redesign followed by an evolutionary update.