992 Tech

We look at the technology inside the newest generation 911.

Photo: 992 Tech 1
The 9A2 Evo engine features numerous detail refinements over its predecessor.
September 12, 2019

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. 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.

Engine & Drivetrain

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). 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. Porsche engineers accomplished this feat by refining many details of the engine and its ancillaries. 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.

This asymmetric valve lift concept has previously been used on the first-generation (9PA) Cayenne S V8 engine of 2003. 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. 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. The “high” lift setting is the same for all intake valves.

Further 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. 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. A solenoid injector uses an electromagnet to lift the injector pintle when voltage is applied, which enables fuel to exit the injector. 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.

Inside each piezo injector body is a stack of hundreds of thin wafers of piezo-electric material, all of which expand slightly when electrical current is applied (at over 100 volts via step-up transformers inside the DME engine control unit). The cumulative expansion of the piezo stack serves to lift the injector pintle indirectly via a pair of small levers, which allows fuel to flow. The precision control enabled by the piezo stack minimizes the “dead time” associated with electromagnetic solenoids, and allows up to five separate injection events per intake cycle at low rpm/high load conditions for optimum atomization of the injected fuel (the previous solenoid injectors were limited to three injections per cycle).

Photo: 992 Tech 2
Adjacent intake valves have a different “small” lift value to promote a homogenous air/fuel mixture.

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. 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. This configuration allows 14 percent larger intercoolers and shortens the air intake air path by 50 percent for better throttle response.

The exhaust manifolds and turbochargers of the 992 were also refined. 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. 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.

These new turbochargers also feature Porsche’s first use of electric controls for the internal wastegate valves. 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. An added benefit of these electric actuators is that they can be used to hold the wastegate valves wide open immediately following cold engine startup to maximize exhaust throughput to the catalytic converters, which helps to solve what has long been an issue with turbo engines. Electric stepper motors are also used to control the bypass flaps for the exhaust mufflers, which allows precision control in the face of ever-stringent drive-by exhaust noise regulations, particularly in the European Union.

Recent EU rules for gasoline DFI engines also require the installation of particulate filters (PF) in the exhaust system, which are integrated into the catalytic converter housings. These ultra-fine honeycomb matrices are designed to trap soot particles; gasoline DFI engines do not generate as much soot as diesel engines, and the average soot particle size tends to be larger, so the grids can be designed with larger pores to reduce exhaust back pressure.

As with diesel applications, the particulate filter system periodically “regenerates,” or combusts the captured soot particles and prevent the trap from becoming clogged. This is achieved by the engine management system temporarily raising exhaust gas temperatures (usually by a combination of retarding ignition timing and leaning out the air/fuel mixture). The higher exhaust gas temperatures of gasoline engines also help to make PF regeneration occur more frequently.

Photo: 992 Tech 3
European-market 992s have soot-capturing particulate filters integrated into the catalytic converter housings.

Porsche claims that the restriction of the PF system is compensated for by integrating it with the catalytic converters and reducing the size of the muffler. Thus far, then PF system is only installed in EU-market cars and not in U.S.-bound 992s, though the California Air Resources Board (CARB) is expected to advance legislation requiring PF systems on gas DFI engines in the near future.

The 992 engine mounting system represents the first major change thereof in the history of the 911 series. Until now, every 911 had an engine bracket bolted to the pulley side of the engine crankcase, with the ends attached to a soft mount at each rear corner of the engine compartment. The 992 uses engine mount brackets which bolt directly to the camshaft covers as in the four-cylinder 718 chassis. The allows the engine mounting to be more rigid without sacrificing comfort, and enables the mounts to be shifted further forward in the chassis to reduce the engine torque effect on the drivetrain. This also improves the effectiveness of the optional Porsche Active Drivetrain Mounts (PADM).

PDK Transmission

The 992 uses an all-new, eight-speed PDK gearbox for power transmission (a seven-speed manual is expected to be released in the near future). This gearbox was developed by ZF and was designed with modularity in mind, as it shares major components and its design concept and layout with the current 971 Panamera PDK unit; as such it also has a void within the bellhousing to allow the installation of an “E-Machine” flywheel unit for a future hybrid 911.

The eight forward ratios are determined by separate loose gearwheels mounted on a pair of concentric input shafts, but to save space some of the fixed gears are shared among ratios. The modular design also allows easy integration of a separate shaft to drive the front wheels of all-wheel-drive 992 variants. This design also allows a wide variety of gear ratios to be used. When compared to the seven-speed PDK of the 991, the 992’s eight gear ratios are shorter and more closely spaced in gears 1-6 (top speed is achieved in 6th gear), with 7th and 8th gears being tall overdrive ratios for high-speed cruising.

As with the 971 version, internal drag and friction is reduced by using a single low-viscosity fluid for both lubrication of the gear clusters and differential gears, and also as the hydraulic fluid for engaging the clutches and shift rod actuators. The fluid pump is a tandem affair, with an electronically-controlled, demand-based pump used for the hydraulic actuators, and a separate gerotor-style pump for gear wheel lubrication (this is driven by the pinion/output shaft to increase the rate of lubrication with road speed).

Photo: 992 Tech 4
The eight-speed PDK transaxle shares its major components and architecture with that of the 971 Panamera.

The front driveshaft and differential unit of the all-wheel-drive Carrera 4 and 4S (and future Turbo versions) has also been refined for efficiency in terms of bearing and seal design. The front differential housing and clutch chamber are now water-cooled to manage the heat generated by the improved actuating torque realized by the latter. This cooling circuit is demand-based to save energy and allow rapid warmup of the differential fluid after a cold start.

Body & Chassis

While Porsche has used a “modular” chassis platform for its mid- and rear-engined sports cars since the days of the 986 and 996, the new 992 chassis aligns with the corporate VW/Audi chassis nomenclature with its “MMB” (modular mid-engine platform) designation. The composition of the previous 991 was already quite aluminum-intensive, but the 992 takes this to new heights with over 70 percent of its structure being aluminum; high-strength steel is reserved for critical passenger safety areas such as the A- and B-pillars and door jambs.

Again, the 992 follows the lead of the 971 with an all-aluminum body side panel, which is attached to the chassis via a special crimping technique. This process occurs in an all-new three-story body production plant at Weissach, which produces bodies for the 718, 992, and upcoming Taycan electric car. This plant features revamped production techniques and processes that are being implemented throughout the VW/Audi Group to improve production efficiency and reduce the environmental impact of the auto-making process.

The most noticeable change to the 992 body are the wider front and rear fenders, which are required to provide coverage to a track width that is 45 mm (1.8 in.) wider up front and 44 mm (1.7 in.) wider at the rear. The wheels themselves also feature staggered wheel diameters for the first time, measuring 19 inches in front and 20 inches rear for the base Carrera and 20 and 21 inches for the Carrera S. Porsche says the larger rear tire contact patch aids traction and stability, while the larger tire carcass allows better heat management.

The 992 carries over the 991’s proven braking system, with 330 mm (13.0 in.) discs and four-piston calipers all around for the base Carrera, with the “S” models using 350 mm (13.8 in.) discs and six-piston calipers in front. The brake pad compounds are all new in response to recent EU environmental regulations banning the use of copper in brake linings (this metal made up about 20 percent of the previous pad compounds). Porsche also replaced the vacuum brake booster of the 991 with a smaller, lighter electronic brake booster, which allows a more direct pedal ratio for better brake feel. Leaving no stone unturned, Porsche managed to save mass at the brake pedal itself by constructing it from the same special organic sheet material used for the 918 supercar’s pedal, which cuts pedal mass by 41 percent while being stiffer than the previous plastic version.

Photo: 992 Tech 5
Over 70 percent of the 992’s body is made of aluminum.

The 992 steering gear is an evolution of the 991’s electric power steering rack, with an 11 percent quicker ratio than its predecessor, or six percent quicker if equipped with the optional rear-axle steering system. A stiffer torsion bar for the steering shaft is installed to provide greater driver feedback, and Porsche designed the electronic controller in-house to further assure that this electric power-assisted steering (EPAS) unit provides the steering feel that the marque is known for. Rear-axle steering-equipped 992s are also supplied with a lightweight lithium-ion battery, which weighs half as much as a conventional lead-acid battery.

The basic suspension layout of the 992 is largely similar to that of the 991, though the wider track allows for softer anti-roll bars and slightly stiffer springs in both the Normal and Sport chassis variants. The other big news is the new Porsche Active Suspension Management (PASM) dampers, which feature Bilstein “DTX” technology controlled by software written by Porsche engineers. These dampers contain an infinitely adjustable magnetic control valve which controls damping forces in response to a suite of sensors mounted throughout the car. The new PASM dampers react to changing conditions within milliseconds, and provide a 30-40 percent greater spread of compression and rebound damping when compared to the 991 version.

As in the 971 Panamera, Porsche has taken its electronic driving aids to the next level in the 992 by using a central Electronic Chassis Platform (ECP) controller to orchestrate all of the driver aids via a high-speed FlexRay bus system. A ride height sensor for each wheel is augmented by feedback from body height sensors front and rear, along with the usual lateral and longitudinal accelerometers and a steering angle sensor to monitor every aspect of chassis operation and regulate the brakes, torque-vectoring differential (PTV), optional Porsche Traction Management (PTM) all-wheel-drive system and engine and transmission controls as necessary to keep the vehicle on the driver’s intended path. Porsche engineers wrote the control software in-house to ensure that the 992 still behaves and feels like a proper 911.

The ECP concept allows for extended capabilities such as the industry-first “Wet Mode.” This system relies upon an acoustic sensor mounted in each of the front wheel housings; these sensors are similar in construction to a radar parking sensor, and are tuned react to the specific acoustic frequency generated by the tires driving over water. If wet conditions are detected, the first stage of Wet Mode operation warns the driver of the condition via the instrument cluster display and prompts the selection of the actual “Wet” driving mode, which tailors everything from throttle response to PASM damper operation to suit the road conditions.

Electronics

Inside the 992, the lead of the 971 continues to be followed, with a central 10.9-inch Thin Film Transistor (TFT) display controlling much of the interior equipment. In the instrument cluster, the traditional analog central tachometer remains, and is flanked by a pair of configurable 7.0 inch TFT displays that mimic the 911 five-gauge layout.

The 992 features standard LED (light-emitting diode) headlights with Porsche’s now-customary four-point daytime running lights. Porsche Dynamic Lighting System (PDLS) actively adjustable headlights are a standalone option, and this is included in the flagship LED-Matrix headlight system. First introduced in the 2014 Audi A8 luxury sedan, these headlights feature a matrix of 84 individual LEDs that operate in full (high) beam mode and automatically adjust the beam to account for oncoming traffic as detected by a camera in the interior rearview mirror. Sadly, this feature is not available in the U.S. thanks to archaic DOT anti-glare laws, but Porsche says that if the law ever changes, full functionality can be enabled via a software change.

The 992 also introduces a full suite of driver assistance features as found in many new automobiles, such as detection of road signs, pedestrians, lane keep assist, and an optional night vision camera. As with the chassis electronics, all of these features are processed by a central driver assistance control unit to implement all of the systems in a seamless fashion. Porsche also says that the system’s capabilities can be expanded via future hardware and software updates.

Also from Issue 268

  • 718 Cayman GT4 Drive
  • 1989 964 Carrera 4 Turbo
  • 935 'Baby' & 991-gen 935
  • Creating the 987 Cayman
  • Market Update: 1974-1989 911
  • EFI Fueled 356B
  • Cayenne Coupe Drive
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