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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 BMW B38 Engine
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].
Engine Specifications
| 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].
Advanced Engine Technology
The three-cylinder unit incorporates BMW’s signature technologies[3]:
- BMW TwinPower Turbo: Twin-scroll turbocharging for rapid response and consistent power delivery
- Valvetronic: Variable valve lift control for precise throttle response
- Double VANOS: Variable valve timing on both intake and exhaust camshafts
- High-pressure direct injection: Optimizes combustion efficiency and reduces emissions
- Plasma-sprayed cylinder liners: Reduces friction and weight compared to iron sleeves
The engine features an aluminum block with closed-deck construction and a balance shaft to minimize vibration inherent to three-cylinder designs[3].
The Hybrid Powertrain System
The BMW i8’s powertrain uniquely separates its gasoline and electric propulsion across different axles[2].
Electric Motor Specifications
| 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] |
Combined System Output
| 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].
Battery System
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].
Driving Modes
The i8 offers multiple driving modes that alter how the hybrid system operates[6]:
eDrive Mode
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].
Comfort Mode
The default setting blends gasoline and electric power for balanced performance and efficiency. The combustion engine cycles on and off based on driving conditions.
Sport Mode
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].
Fuel Economy and Efficiency
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.
Why a Three-Cylinder in a Sports Car?
BMW’s decision to power the i8 with a three-cylinder engine initially surprised enthusiasts[8]. The rationale behind this unconventional choice included:
Weight Distribution
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.
Hybrid Synergy
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].
Efficiency Goals
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].
Production History
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.
Key Takeaways
- The BMW i8 is powered by a 1.5-liter turbocharged three-cylinder B38 engine producing 228 hp, paired with a 141 hp front electric motor for 369 combined horsepower
- The i8 was the first BMW production vehicle to use a three-cylinder engine, achieving the highest specific output (154 hp/liter) of any BMW Group engine at launch
- The hybrid system creates through-the-road all-wheel drive: the gasoline engine powers the rear wheels while the electric motor drives the front
- Battery capacity increased from 7.1 kWh (2014-2017) to 11.6 kWh (2018-2020), extending pure electric range to approximately 18 miles
- Production ran from 2014 to June 2020 at BMW’s Leipzig plant, with over 20,000 units sold worldwide
Frequently Asked Questions
Is the BMW i8 engine reliable?
The B38 three-cylinder engine in the i8 is generally considered reliable, with an estimated lifespan of approximately 300,000 km (186,000 miles) when properly maintained[3]. The engine requires 0W-30 or 0W-40 synthetic oil and has a 4.25-liter oil capacity[3]. Common maintenance items include the timing chain and turbocharger service, which should be inspected according to BMW’s maintenance schedule.
How fast is the BMW i8?
The BMW i8 accelerates from 0-60 mph in 4.2 seconds and reaches an electronically limited top speed of 155 mph[1]. The combined system torque of 420 lb-ft provides strong acceleration, with the electric motor eliminating turbo lag at low speeds[1]. Performance is comparable to many V6-powered sports cars while delivering significantly better fuel economy.
What is the difference between the i8 Coupe and Roadster?
Both the BMW i8 Coupe and Roadster share identical powertrains: the 1.5L three-cylinder engine and electric motor producing 369 combined horsepower[6]. The Roadster features a folding soft top that can be operated at speeds up to 31 mph. The Roadster weighs slightly more and seats only two passengers, while the Coupe offers 2+2 seating. Both body styles were available from 2018 until production ended in 2020[6].
Can the BMW i8 run on just gasoline?
Yes, the BMW i8 can operate without an electric charge using only its 1.5-liter TwinPower Turbo gasoline engine[11]. In this mode, the EPA rates fuel economy at approximately 29 mpg[7]. However, performance is optimized when the battery is charged, as the electric motor provides additional torque and eliminates the delay from the turbocharged engine.
Did BMW make an i8 successor?
BMW has not released a direct replacement for the i8. The company discontinued the model in 2020 and shifted focus to fully electric vehicles like the i4, i5, i7, and iX[9]. BMW has hinted at potential future electric sports cars, but no official successor to the i8’s plug-in hybrid sports car formula has been announced as of 2025.
References
- BMW Palm Springs. (2024). BMW i8: A Legacy Powering Today’s BMW’s Plug-In Hybrid Lineup. https://www.bmwpalmsprings.com/bmw-i8
- Drive i8. (2022). BMW i8 Performance and Power. https://drivei8.com/bmw-i8-performance-and-power/
- My Motor List. (2022). Engine specifications for BMW B38, characteristics, oil. https://mymotorlist.com/engines/bmw/b38/
- Wikipedia. (2024). BMW i8. https://en.wikipedia.org/wiki/BMW_i8
- AutoData1. (2024). BMW i8 Coupe (I12) 1.5/7.1 kWh (362 Hp) Hybrid Automatic. https://www.autodata1.com/en/car/bmw/i8/i8-coupe-i12-1571-kwh-362-hp-hybrid-automatic
- Carl Thompson. (2019). BMW i8 Roadster / Coupe Review (differences of the two). https://www.carlthompson.co.uk/further-reading-blogs/2019/3/24/bmw-i8-roadster-coupe-review-differences-of-the-two
- Savini Wheels. (2019). BMW i8. https://saviniwheels.com/vehicles/bmw-i8-2/
- Reddit r/cars. (2017). How is it possible for the BMW i8 to have a 1.5L 3-cylinder? https://www.reddit.com/r/cars/comments/6uey2x/how_is_it_possible_for_the_bmw_i8_to_have_a_15l/
- SlashGear. (2024). Here’s Why The BMW i8 Was Discontinued. https://www.slashgear.com/1605576/why-bmw-i8-discontinued-what-happened/
- BMW Group Press. (2020). Final 18 BMW i8 cars leave Plant Leipzig. https://www.press.bmwgroup.com/global/article/detail/T0309945EN/final-18-bmw-i8-cars-leave-plant-leipzig
- BMW USA. (2024). Legacy BMW i8 Coupe and BMW i8 Roadster. https://www.bmwusa.com/legacy-vehicles/i8.html
I am a senior automotive analyst at Autvex. Expert vehicle evaluations, in-depth reviews, and objective analysis helping readers make informed automotive decisions with years of industry experience.
