An electrified series-production 911 has been rumored since Porsche released the one-off GT3 R Hybrid race car in 2011. As mentioned in the September 2019/#268 tech feature about the 992.1-generation 911, the ZF-built eight-speed PDK gearbox contained a void to allow the fitment of an “E-Machine” electric motor. Several cycles of rumors about the introduction of a hybrid 992 ensued, but it wasn’t until 2024 that the 992.2 Carrera GTS T-Hybrid was announced.
Porsche has committed to expanding the T-Hybrid range with the recent introduction of the 992.2-gen Turbo S, which will ensure compliance with recently introduced Euro 7 exhaust emission compliance in the European Union. The following will focus on the combustion engine changes and “T-Hybrid” system of the 992.2 Carrera GTS and Turbo, while highlighting the differences between the two cars.
The Origins of eTurbo Technology
Since the 2014 season, both Formula One and the period LMP1 prototype sports racing cars of the World Endurance Championship (WEC) employed hybrid electric drivetrains to promote improved efficiency and sustainability. One of the means of recharging the onboard high-voltage battery in either race series was by harvesting heat energy from the exhaust using an electric motor built into the turbocharger assembly (known as the MGU-H or Motor/Generator Unit-Heat in F1 parlance). Porsche’s 919 Hybrid race car used an MGU-H, which differed in layout from the current T-Hybrid described below, while most F1 cars use a similar system to what is now offered in production Porsche 911s.
9A3 Combustion Engine
Porsche introduced its next-generation 9A3-series flat-six family of engines with the 992.2 Carrera GTS for the 2025 model year. The GTS and Turbo S versions of the 9A3 share the same bore and stroke, and the same lightened crankshaft, along with the engine block halves and cylinder heads. In contrast to the usual Porsche trend of over-square bore-to-stroke ratios (the 992.1 Turbo achieved 3.8 liters with a 102 mm bore and 76.4 mm stroke), the new 3.6-liter unit has a 5.0 mm narrower bore and a 4.6 mm longer stroke than the previous 3.8-liter Turbo S. The new Turbo S has stronger cast pistons with a lower 9.2:1 compression ratio versus 10.2:1 for the Carrera GTS.
The redesigned cylinder heads are more compact thanks to GT3-like finger followers with solid lifters replacing the previous bucket tappets, which eliminates the possibility of the new engine using Porsche’s VarioCam Plus dual-stage valve lift system. This was considered a worthy sacrifice by Porsche engineers, given the broadened torque curve allowed by the T-Hybrid system. At 18.9 psi of turbocharger boost, the 3.6-liter GTS engine manages a modest five horsepower (478 vs. 473 hp) improvement over its 3.0-liter 9A2 predecessor, thanks to the Euro 7 regulations outlined below, while the Turbo S squeezes the same 640 hp as its predecessor from a 3.6-liter engine, thanks to 26.1 psi of boost.
Porsche engineers managed to achieve such a high specific output from the combustion engine with a more compact version of its expansion intake manifold (see the September 2019/#266 tech feature) that has 11.0 cm/4.3 inches less height to allow room for the pulse inverter and the DC/DC converter for the 400-volt system, along with the high-voltage distributor module and the DME control module for the combustion engine. The high-voltage air conditioning compressor is nestled between the intake manifolds. The engine oil filter was relocated from the top to the bottom of the engine to allow room for the additional components. The Carrera GTS engine has a single throttle body and a large single air-to-air intercooler mounted aft of the intake manifold, while the Turbo S has a dual-tract intake system with an intercooler and a throttle body for each bank.
By eliminating the accessory belt drive, the 992.2 GTS engine gains the space needed to accommodate its more complex exhaust system.
Meeting Euro 7:
Lambda 1.0 Combustion
The April 2025/#316 tech feature about combustion mentioned the recent Euro 7 exhaust emission requirements for gasoline engines to operate with a stoichiometric (represented by the Greek letter Lambda) air/fuel ratio of 14.7 parts of air (by mass) to one part fuel to achieve optimal combustion and minimize emissions of hydrocarbons (HC, or unburnt fuel), carbon monoxide (CO) and oxides of nitrogen (NOx in automotive parlance).
Previous emissions standards were strict enough to require engines to run at Lambda 1.0 under most operating conditions, but still allowed richer air/fuel ratios under full load conditions, with the extra fuel being used to cool the engine combustion chambers to protect against abnormal and destructive forms of combustion such as detonation (also known as “spark knock” or “pinging”).
The Euro 7 requirements for Lambda 1.0 present a great challenge to the designers of high-performance combustion engines, as the leaner air/fuel ratios under full load do not allow nearly as much ignition timing advance and/or turbocharger boost, which reduces power output. Porsche’s solution is their high-voltage “T-Hybrid” system to augment the redesigned combustion engine, which allows larger turbochargers with much less exhaust backpressure, in turn allowing safe combustion engine operation at Lambda 1.0 and high boost pressures.
T-Hybrid Basics
The Porsche T-Hybrid system is designed primarily to increase performance beyond that of the 992.1 Carrera GTS and Turbo S predecessors while meeting the Euro 7 exhaust emission requirements. As such, it is not focused on minimal energy consumption—the vehicle cannot be powered by the electric motor alone. The combustion engine always runs, and the high-voltage battery is focused on maximum energy deployment rather than energy storage capacity.
The high-voltage motor acts as both a starter and a generator, and the air conditioning system is powered by the 400V circuit, so the engine belt drive is eliminated, which saves 40 lbs to offset the overall weight gain of the system. The Turbo S electric motor results in a 60-hp increase in power for 701 hp total, and a broad, flat torque curve: 590 lb-ft from 2,300-6,000 rpm (80 hp/139 lb-ft).
The eTurbo has a 27-hp electric motor sandwiched between the impeller and turbine housings.
Energy for the 400V system is derived from a compact 1.9 kWh (1.5 kWh usable) lithium-ion battery, which resides in the same place as the starter battery of a conventional 992. Weighing only 27 kg (59 lbs) and made by Porsche partner Rimac, the battery pack is composed of two layers of cylindrical 2171 cells (216 cells total), with a capacitor-like construction designed more for rapid discharge and recharge rates to provide 40 kW of instant electrical power to the eTurbos and electric traction motor. The maximum discharge power of 50 kW requires a dedicated water cooling circuit and a battery management system to maintain stable cell temperatures, given the amount of current and heat generated.
The vehicle’s 12V system is powered by a compact (90 mm, or 3.5 in., height) 40 Ah LiFePO4 battery mounted under the rear parcel shelf, which weighs only 15 lbs. The 12V battery is charged via a DC-to-DC converter, with remote charging posts located adjacent to the 400V battery in the cowl area.
eTurbos
The heart of the Porsche T-Hybrid system is the electric turbocharger, “eTurbo” in marketing parlance, and dubbed “eATL” in Porsche’s workshop literature for “auspuff turbolader” or exhaust-gas turbocharger. The Carrera GTS’s single turbocharger assembly contains a 27-hp electric motor sandwiched between the compressor and turbine housings (83 mm compressor wheel, 80 mm turbine wheel). The motor is used to quickly spool up the turbo up to its maximum speed in 0.8 seconds, according to Porsche. Once the electric spool-up has peaked, energy from the expanding exhaust gas molecules driving the turbine wheels is used to maintain impeller speed as in a conventional turbocharger.
The Porsche eTurbo design eliminates the need for a wastegate to limit impeller speed. Once the boost target is reached, the motor functions as a generator to act as a brake on the rotating mass and limit its speed to 125,000 rpm, which also has the benefit of generating almost 11 kW of power, which can be used to either recharge the high-voltage (HV) battery or augment the E-machine in the transmission bell housing. Therefore, the energy that would normally be diverted to the exhaust stream by a wastegate is harvested to help propel the vehicle. Exhaust gas temperatures are also decreased thanks to the decreased back pressure and increased exhaust throughput allowed by the larger turbine housing(s).
The Turbo S features twin eTurbos, each with the same motor as the single GTS version, but with 73 mm compressor wheels and 65 mm compressor wheels, which increase responsiveness and allow maximum shaft speeds of 145,000 rpm. Twin turbochargers also allow a higher energy recuperation rate than the Carrera GTS, with 22 kW possible. Full-throttle application in fourth gear at 1,500 rpm results in peak boost a full two seconds sooner than in a 992.1 Turbo with its Variable Turbine Geometry (VTG) turbochargers.
E-Machine/Traction Motor
& PDK Transaxle
Both T-Hybrid configurations use an eight-speed PDK transaxle with strengthened gear sets, clutches, and final drive gears to withstand the increased torque output. A permanent-magnet synchronous motor (PMSM, see the August 2015/#229 hybrid article) is sandwiched between the engine and transaxle, as in other Porsche hybrid applications. The Carrera GTS version provides 40 kW/54 hp and 110 ft-lbs of torque, while the Turbo S can add up to 60 kW/80 hp with the same E-motor thanks to the additional harvesting abilities of the second eTurbo.
The eight-speed PDK transmission with its integrated E-motor.
While most electrified applications use the electric traction motor for torque-filling to augment the combustion engine until the turbochargers are spooled, Porsche’s T-Hybrid strategy deploys the maximum 40 kW usable discharge power of the HV battery directly to the eTurbo(s) for maximum spool-up. Once peak boost and rotating speeds are achieved, energy is harvested from the exhaust gas to either power the E-Machine or to recharge the HV battery if its State of Charge (SoC) is low.
The relatively compact T-Hybrid system results in much less weight penalty than most other hybrid setups—the 992.2 GTS version adds only 103 lbs compared with the 992.1 GTS, while Porsche states that the 992.2 Turbo version is 85 kg/187 lbs heavier than its predecessor.
The T-Hybrid system does not rely much on regenerative braking to recharge the HV battery because the small 1.9 kWh capacity and rapid charging ability would quickly recharge the battery to 100 percent, with no additional means of energy storage. This allowed Porsche engineers to maintain a consistent brake pedal feel without complex algorithms to blend regenerative and friction braking regimes.
Exhaust Emission Controls
The exhaust systems of the Carrera GTS and Turbo S are functionally the same, but with drastically different layouts due to the single versus twin turbocharger configurations—both are marvels of packaging efficiency. The GTS turbo outlet is attached to a large monolith containing a particulate filter and a three-way catalytic converter, mounted across the rear of the car to a large single muffler assembly to the left of the engine. The leftmost of the central tailpipes is attached to the muffler, with the right tailpipe being attached to the catalyst to bypass the muffler when Sport and Sport Plus modes are engaged.
As with the intake side, the Turbo S exhaust system features parallel exhaust paths for each bank, which mirror each other in terms of layout, with a muffler at each side and the catalyst/Gasoline Particulate Filter (GPF) assembly in between. Each bank features an electric bypass valve for improved exhaust flow and sound.
Both the Carrera GTS and Turbo S feature fully functional and monitored gasoline particulate filters (see the October 2021/#285 tech feature for more info). A differential pressure sensor is used to monitor the difference in exhaust back pressure before and after the GPF, with too much of a delta triggering a regeneration phase when the required driving conditions are met. In the event of a clogged GPF, with requisite fault codes and a “check engine” light, a forced GPF regeneration procedure can be initiated in a workshop with a Porsche Integrated Workshop Information System (PIWIS) tester.
The 992.2 Turbo S engine featuring twin eTurbos and twin throttle bodies.
Porsche further leveraged the functionality of the eTurbo by operating it as a secondary air injection pump immediately after a cold start. Instead of a separate 12V air injection pump as used in previous Porsche applications, the high-voltage eTurbo motor is operated at a relatively low speed, and a pair of electric changeover valves (one for each cylinder bank) divert a portion of the air ingested by the impeller portion of the eTurbo(s) to the exhaust system downstream of the exhaust manifolds.
This is the only condition during which the combustion engine is allowed to operate richer than Lambda 1.0 (about 0.8 in this case), with an additional injection sequence during the compression stroke. The additional fuel combines with the extra air in the exhaust stream to constitute an overall mixture of about Lambda 1.0, thus enabling rapid warmup of the three-way catalytic converter.
High-Voltage Chassis Controls
Optional on the Carrera GTS and standard on the Turbo S is Electro-hydraulically controlled PDCC (ehPDCC), which uses the 400V system to actuate the cross-linked hydraulic rams to control body roll. 400V operation allows a more rapid response than that of the previous 12V system, along with a more compact electrohydraulic motor/pump unit. The optional front axle lift system also operates via the 400V for faster response.
T-Hybrid Care & Maintenance
Because the T-Hybrid HV battery cannot be charged externally, care must be taken not to allow its SoC to fall below 30 percent if the vehicle is to be parked for two weeks or more. If the vehicle is to be stored for two months or more, Porsche recommends charging the HV battery to 80 percent SoC by driving for several minutes in the Sport Plus driving mode, with its aggressive recuperation regime. Porsche also stipulates that an approved trickle charger for the 12V LiFePO4 vehicle electrical system be connected to the remote positive and negative posts.
Because external energy cannot be used to precondition the car’s interior temperature, Porsche also recommends against regularly parking a T-Hybrid car in bright sunlight and high ambient temperatures. The energy required to first start the combustion engine and then use maximum air conditioning capability via the high-voltage A/C compressor could rapidly deplete the HV battery.
If the HV battery SoC falls below 10 percent, the vehicle must be towed to a Porsche Center for an emergency starting procedure. This requires connecting a PIWIS tester and initiating a sequence that involves using a 90-amp power supply/battery charger for the 12V system, with the eventual result being the high-voltage contactors closing and enabling the combustion engine to start via the electric motor, thus allowing the normal charging regime to commence.
