Testing has proven engineers’ original simulations, so the car will proceed with very few changes. Nestled behind the back seats is a tiny 161-horsepower combustion engine linked to a compact double-clutch gearbox to drive the rear wheels. That isn’t enough to do the acceleration numbers BMW promised: 0-62 mph in 4.8 seconds.

So between engine and box, a disc-shaped motor adds a peak 51 horsepower. Another bigger motor adds up to 139 horses to the front wheels, in bursts of up to 10 seconds. Any longer and the batteries would overheat, so the front motor drops to 80 horses in steady-state running.

Overall system power becomes 323 horses. The test car’s engine is a tiny 1.5-liter three-cylinder diesel, which would achieve the claimed economy figure. The car will have enough battery capacity to act as a plug-in hybrid electric vehicle, giving a claimed electric-only range of 30 miles.

The 2+2 weighs 3100 pounds, including batteries, enabled by widespread use of carbon fiber. Low mass is critical to squeezing good performance out of this powertrain, but so is low aerodynamic drag. Thanks to the concept’s very low frontal area, the drag coefficient was just 0.22. Its “layered” construction has outer body panels mounted to the main body structure with a gap to channel air to critical parts such as the brakes, while creating little turbulence.

Ian Robertson, BMW‘s board member for sales and marketing, says it’s “brilliant” to drive, but very different from a normal sports car.

He says that it would be a low-volume, high-price car. Certainly with the M3, BMW will offer more bang for the buck. But, as development chief Klaus Draeger says, this one is a “brand shaper for BMW,” a car to get it out of its technological stall.