The two high-end sportscars are not exactly running in the same category but with a close enough price point and performance, one customer might choose one over the other.
Before jumping into the driving review, here are the upfront stats:
Price £94,845 (including government grant); 0-62mph 4.4sec; Top speed 155mph; Economy 135mpg (combined); CO2 49g/km; Kerb weight 1485kg; Engine 3 cyls in line, 1499cc, turbo, plus electric motor; Power 357bhp at 5800rpm; Torque 420lb ft at 3700rpm; Gearbox 6-spd auto (petrol), 2-spd auto (electric)
Porsche 911 50th Anniversary Edition PDK
Price £103,251; 0-62mph 4.2sec; Top speed 187mph; Economy 32.5mpg (combined); CO2 205g/km; Kerb weight 1430kg; Engine 6 cyls horizontally opposed, 3800cc, twin-turbo, petrol; Power 424bhp at 7500rpm; Torque 325lb ft at 5750rpm; Gearbox 7-spd dual
The initial impression is that the i8 offers a very different driving experience from any traditional BMW sports car. There is an uncharacteristic lightness to the controls and a faint whine from the electric motor under load but, for the most part, the impression is of outstanding mechanical refinement.
The electric motor drives through a two-speed automatic gearbox, providing instantaneous responses and the sort of standing start acceleration to allow the i8 to challenge a well sorted hot hatchback away from the traffic lights in electric mode.
Drive it in isolation over a flowing back road without too many tightening second-gear corners and you may never doubt the dynamic ability of the i8. The steering is precise, if a little light, while turn-in is urgent and it happily accepts increasing lateral forces without awkward body movements.
With its electric motor and combustion engine channelling their combined reserves to all four wheels, there is plenty of traction and the brakes are powerful, albeit lacking in ultimate pedal feel. And besides some annoying patter at the front over pockmarked surfaces, the ride is quite compliant for a car of such sporting pretensions.
And boy, does it go when you put your foot down on the exit of a bend. On smooth roads, it is capable of keeping the rear-engined 911 honest, which speaks volumes for the effectiveness of its high-tech driveline. The Porsche has nothing like the same amount of low to mid-range torque; nor does it possess anywhere near the initial accelerative force out of corners.
But the 911 is not gutless. Above 4000rpm, its naturally aspirated engine provides prodigious shove. But by then, the i8 has already benefited from its initial spurt of electric propulsion and is away down the road. BMW claims 0-62mph in 4.4sec, compared with 4.5sec for the Porsche. However, a constant, linear surge of energy right from the outset makes the i8 feel considerably faster.