Rather than go through all the associated development costs of building an electric car from the ground up, Cincinnati-based Advanced Mechanical Products (AMP) has decided to replace GM's four-cylinder petrol engine in its Saturn Sky roadster with its own electric motor. This effectively turns the Saturn Sky roadster into an all-electric vehicle you can charge up at home.

Running on lithium phosphate batteries, the electric motor pushes the car to 60mph in 5.7 seconds but the trade-off is a lower top speed of 90mph. The car’s acceleration is significantly faster than the petrol Saturn Sky thanks to the electric motor's ability to utilize maximum torque instantaneously but by the same token top speed is hampered in order to maximize driving range.

According to AMP, the car can be charged to give a range of 150 miles - significantly more than GM's upcoming Volt which has been set a target of only 40 miles of electric-only driving. Production of the electric Saturn Sky will be limited to just 300 units and will set you back around $50,000 - about double the price of the base petrol model.

AMP now plans to carry out its engine-replacement approach in several other Saturn models, including sedan and SUV models.