Formula One used naturally aspirated V8 engines from 2006 through 2013, with kinetic energy recovery systems (KERS) introduced on an optional basis in 2009. The KERS concept recovered energy under braking and redeployed it as an acceleration boost capped at 81 horsepower for approximately six seconds per lap. All four teams that trialled it — Ferrari, Renault, BMW, and McLaren — used electrical storage rather than mechanical flywheel variants. KERS became standard across the grid by 2013, laying the regulatory and engineering groundwork for the full hybrid power unit.
The 2014 regulations represented a fundamental reorientation. The FIA announced in advance that a 1.6-litre V6 turbocharged hybrid would replace the 2.4-litre V8, introducing both a kinetic and a heat energy recovery system under a fuel flow restriction of 100 kilograms per hour rather than a boost pressure limit. Engine manufacturers Mercedes, Ferrari, and Renault each produced units to the new formula; Honda returned to Formula One in 2015.
The MGU-K is an electric motor-generator connected to the crankshaft at a fixed ratio, with a maximum rotational speed of 50,000 rpm. It operates in two modes: under braking it acts as a generator, converting the kinetic energy of deceleration into electrical energy stored in the battery; under acceleration it draws from the stored energy and drives the crankshaft as an electric motor. The MGU-K is permitted to recover a maximum of 2 megajoules per lap and deploy a maximum of 4 megajoules per lap from the energy store. Its power output is capped at 120 kilowatts, equivalent to approximately 160 horsepower.
The MGU-K in effect replaced and greatly expanded the earlier KERS system, with both its recovery and deployment allowances substantially higher than the KERS cap. Its deployment by the driver is managed through the steering wheel, allowing tactical use of electrical boost in addition to the power provided by the combustion engine.
The MGU-H is an electric motor-generator located on the common shaft linking the exhaust turbine and intake compressor of the turbocharger, running at the same speed as the turbocharger itself up to a maximum of 125,000 rpm. This position between the exhaust turbine and compressor gave the MGU-H two distinct functions.
As a generator, the MGU-H could harvest electrical energy from the exhaust gas flow driving the turbocharger in a process known as harvesting. When the turbocharger was being driven conventionally by exhaust gas, the MGU-H would spin with the shaft and generate electricity. This came at a cost to overall power but enabled net lap-time gains when harvesting was done on sections of track not requiring peak power — for example, at the end of straights or between certain corners — and the stored energy was deployed elsewhere.
As a motor, the MGU-H drove the compressor turbine electrically using stored battery energy. This allowed the turbocharger to reach peak boost pressure almost instantly, effectively eliminating turbo lag by electrical means. On demand — particularly during qualifying laps and in strategic race moments — energy could be directed to the MGU-H to spin the turbine even at high engine RPM, at which point exhaust gas could be bypassed through the wastegate; this was estimated to increase power by between 5 and 10 percent at a cost to stored energy levels.
Unlike the MGU-K, the MGU-H faced no regulatory limit on energy recovered or deployed per lap, giving teams freedom to use it as continuously as cooling and reliability permitted.
The 2015 season saw most manufacturers add 30 to 50 horsepower over their 2014 benchmarks. Mercedes produced the most powerful unit in 2015 at approximately 870 horsepower combined. By 2019, Renault claimed its engine had exceeded 1,000 horsepower in qualifying trim. Honda's RA621H unit of the 2021 season generated over 100 kilowatts more maximum power than Honda's RA615H of 2015 at the same fuel flow rate — a clear indicator of how far combustion efficiency, software, and hybrid integration had advanced within the frozen architecture.
The improved thermal efficiency of the 2014–2025 power unit era also reduced heat and noise output compared to the naturally aspirated V8 era. Brake mean effective pressure rose from approximately 14 bar in the V8 period to 40 bar and beyond by the early 2020s through lean and rapid burn combustion techniques.
Negotiations for the successor regulations began in 2017 with the original intent of abolishing the MGU-H — viewed as too complex and expensive for new manufacturers to develop — and increasing the MGU-K's output. No new manufacturers joined for 2021 or 2022, so those changes were deferred, with the architecture frozen from 2022 to 2025.
The 2026 power unit regulations ultimately removed the MGU-H and substantially increased the MGU-K's allowable output from 120 kilowatts to 350 kilowatts (approximately 470 horsepower), while the internal combustion engine's contribution was reduced to approximately 400 kilowatts, producing an approximately 50-50 split between combustion and electrical power at over 1,000 horsepower combined. Audi entered Formula One as a new manufacturer under the 2026 regulations, and Ford partnered with Red Bull Powertrains. Honda, through Honda Racing Corporation, returned as a manufacturer. Renault confirmed in September 2024 that it would exit engine supply at the end of the 2025 season and would not supply power units for the 2026 regulations.