The BMW i8 features a 1.5-liter turbocharged three-cylinder gasoline engine (BMW B38) paired with an electric motor to create a plug-in hybrid powertrain producing 369 combined horsepower[1]. The gasoline engine generates 228 hp and 236 lb-ft of torque, while the front-mounted electric motor adds 141 hp and 184 lb-ft of torque[2]. This unique setup made the i8 the first BMW production car powered by a three-cylinder engine and achieved a 0-60 mph time of 4.2 seconds[1].
The i8's gasoline engine is designated as the BMW B38K15T0, a hybrid-specific variant of BMW's modular B38 three-cylinder engine family[3].
| Specification | Value |
|---|---|
| Engine Code | B38K15T0[3] |
| Displacement | 1,499 cc (1.5L)[4] |
| Configuration | Inline 3-cylinder[4] |
| Valvetrain | 12-valve DOHC[3] |
| Bore x Stroke | 82mm x 94.6mm[3] |
| Compression Ratio | 9.5:1 (hybrid version)[3] |
| Max Power | 231 PS (228 hp) @ 5,800 rpm[4] |
| Max Torque | 320 Nm (236 lb-ft) @ 3,700 rpm[4] |
| Fuel System | Direct injection[3] |
| Turbocharging | Continental twin-scroll turbo (water-cooled)[3] |
The B38 engine in the i8 achieves an extraordinary specific output of 154 hp per liter, which at the time of its release was the highest of any BMW Group production engine and comparable to high-performance sports car powerplants[4].
The three-cylinder unit incorporates BMW's signature technologies[3]:
The engine features an aluminum block with closed-deck construction and a balance shaft to minimize vibration inherent to three-cylinder designs[3].
The BMW i8's powertrain uniquely separates its gasoline and electric propulsion across different axles[2].
| Specification | Value |
|---|---|
| Type | AC Synchronous Electric Motor[2] |
| Position | Front axle[2] |
| Max Power | 141 hp @ 4,300 rpm[2] |
| Max Torque | 184 lb-ft (250 Nm) @ 0-4,100 rpm[2] |
| Transmission | 2-speed automatic[5] |
| Specification | Value |
|---|---|
| Combined Horsepower | 369 hp[1] |
| Combined Torque | 420 lb-ft[1] |
| 0-60 mph | 4.2 seconds[1] |
| Top Speed | 155 mph (electronically limited)[5] |
The gasoline engine powers the rear wheels through a 6-speed automatic transmission, while the electric motor drives the front wheels through its own 2-speed gearbox[2]. This creates a hybrid-specific all-wheel-drive system where power distribution is managed by BMW's intelligent energy management software[6].
The i8 underwent a battery upgrade during its production run[2]:
| Model Years | Battery Capacity | Electric Range (EPA) |
|---|---|---|
| 2014-2017 | 7.1 kWh[2] | 15 miles[7] |
| 2018-2020 | 11.6 kWh[2] | 18 miles[1] |
The larger battery in later models extended pure electric driving capability to speeds up to 75 mph (120 km/h)[6].
The i8 offers multiple driving modes that alter how the hybrid system operates[6]:
Pure electric operation using only the front electric motor. The 2018+ models can travel at up to 75 mph on electric power alone before the gasoline engine engages[6].
The default setting blends gasoline and electric power for balanced performance and efficiency. The combustion engine cycles on and off based on driving conditions.
Activates both powertrains simultaneously for maximum acceleration. The electric motor provides instant torque boost during hard acceleration while the turbo engine delivers sustained power[6].
The hybrid system delivers impressive efficiency figures for a sports car[7]:
| Metric | Value |
|---|---|
| EPA Combined (electric+gas) | 76 MPGe[7] |
| Gasoline-only mode | 29 mpg[7] |
| NEDC Combined | 134.5 mpg[7] |
| CO2 Emissions | 49 g/km[5] |
Real-world fuel economy varies significantly based on driving style and how often the battery is charged. Owners who regularly plug in their i8 can achieve exceptional efficiency in daily commuting.
BMW's decision to power the i8 with a three-cylinder engine initially surprised enthusiasts[8]. The rationale behind this unconventional choice included:
The compact three-cylinder engine allowed BMW to position it as a mid-rear unit, achieving near-perfect 50:50 weight distribution[4]. A larger engine would have compromised the i8's packaging and handling balance.
The gasoline engine was never designed to work alone. Combined with electric torque-fill from the front motor, the system eliminates turbo lag and provides continuous power delivery that masks the smaller displacement[2].
BMW's goal was proving that electrified sports cars could deliver exotic performance without exotic fuel consumption. The three-cylinder's high specific output demonstrated that smaller displacement plus electrification could compete with traditional V8 and V6 sports cars[4].
The BMW i8 was produced from 2014 to June 2020 at BMW's Leipzig plant in Germany[9]. BMW announced the end of production on March 11, 2020, with the final 18 units—all Roadsters—built in June 2020[10].
During its six-year production run, BMW sold over 20,000 i8 units worldwide, making it the best-selling hybrid sports car in history at the time of its discontinuation[9].
For those interested in BMW's current electric offerings, see our guides on the BMW i4 and BMW iX.
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