German Porsche tuner Ruf has produced the world’s first professionally built electric 911, the eRUF. The prototype replaces the flat six engine with a brushless three-phase motor powered by lithium-ion batteries. Although not as quick as a petrol-engined 911, Ruf’s engineers say the eRUF is still good for a 0-100km/h (60mph) time of under 7.0sec and has a top speed of 255km/h (160mph). More importantly it’s claimed to have a maximum range of nearly 320km (200 miles).

The battery pack provides 317-volts and 480-amps and consists of 96x 160Ah Axeon lithium-ion iron-phosphate cells, each weighing 5.6 kg (12.3 pounds). Total weight of the pack is 550 kg (1,213 lbs). The pack is constantly monitored by a battery management system from Axeon. Each individual cell is coupled with a sensor that sends information on cell temperature and voltage to the central control system. The cells, with a nominal voltage of 3.3 V, have a lifespan of 3,000 charging cycles. Pack capacity is 50.72 kWh which is around the same capacity as the battery pack found in the Tesla Roadster but at 318 kg (700 lbs) the Tesla pack is 232 kg (513 lbs) lighter than the eRUF battery pack.

The eRUF prototype utilizes a 150kw (204hp) brushless three-phase BLDC motor supplied by UQM in place of Porsche's traditional 345 hp flat six. The electric motor makes around 650 Nm (480 lb-ft) of torque that, like other electric cars, can be had immediately from zero rpm. Unfortunately though, because of the weight of the batteries, Ruf's modifications push its weight up to 1920 kg (4202 lbs) versus a base 911 Carrera S weight of 1420 kg (3124 lbs)

Ruf engaged CALMOTORS in Camarillo, California, specialists in the implementation of hybrid electric and electric only power train design, to combine the latest generation of lithium-ion batteries with the UQM motor. Since the 150 kW electric motor unit is very compact, there is a lot of room for batteries in the Ruf's bodywork. The eRUF remains rear wheel drive with the motor and the bulk of the batteries positioned over and behind the car’s rear axle. The eRUF also retains the standard 6 speed manual gearbox which contributes to the car being overweight, no doubt to be replaced with a lighter and more energy efficient single speed transmission in the production version.

The eRUF is still in the development stage, and the firm says the car’s performance and range will increase with improvements in battery technology.

Paul Evans

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