How does the BMW i8 hybrid’s tiny engine hit 250km/h?

Automakers have consistently worked to get more power out of smaller engines, but an upcoming BMW model may take the crown. The i8, a sports model planned for sale in Canada next year, accelerates to 100 km/h in 4.5 seconds and can reach 250 km/h—and it’s a hybrid with only a three-cylinder engine.

I had an exclusive opportunity to drive a heavily-disguised model at the company’s test track in France, where the i8 proved it can run on electricity alone in the city, or hold its own at high speeds with some of the best of today’s conventional competitors.

“We need the ability for emission-free driving,” says Dr. Carsten Breitfeld, vice-president of BMW and director of the i8 program. “There will be a clear need for every powertrain in the future to reduce fuel consumption at its maximum.”

The i8 combines a variety of technologies. Its front wheels are powered by an electric motor, mated to a two-speed transmission that the car uses when running on battery only. After it’s recharged by plugging into a wall, the i8 can run almost silently for 35 km on electricity. That’s primarily for city use, but it can reach 120 km/h on the battery alone.

The rear wheels are powered by a turbocharged 1.5-litre three-cylinder engine, with a six-speed automatic transmission. During regular and performance driving, the i8 uses a combination of electricity and gasoline, using regenerative braking to recharge the battery while driving. The gas and electric systems, working together, produce 362 horsepower and 420 lb-ft of torque, comparable to what some eight-cylinder engines make.

Since both axles have their own power source, the i8 is all-wheel drive, which improves its handling. Electric motors make their power right away, while gasoline engines have to rev up. BMW solves this disparity with a small, high-voltage electric motor at the rear, which can provide additional power to the rear axle on acceleration.

To offset the heavy powertrain and battery, the i8 is made exclusively of lightweight materials, including an aluminum chassis, carbon fibre body, and plastic panels. The entire car weighs about 1,490 kg.

“What we put into the electric motor, we cut out of the (gasoline) engine,” Breitfeld says. “The smaller engine gives smaller fuel consumption, while the electric motor makes it dynamic.”

Very pricey

  • Forecast. BMW estimates that the i8 will get 2.9 L/100 km in combined hybrid driving, and use less than 10 L/100 km in racetrack-style driving.

  • Cost. Estimates for the i8’s Canadian pricing range from $160,000 to $180,000.

  • Sequel. The i8 is the second car in BMW’s “innovation” series, following the all-electric i3 city hatchback.

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