The General Motors Stir-Lec I was a concept hybrid electric car based on the Opel Kadett body in 1969. The power plant consists of 14 lead-acid batteries in the front of the car which transfer energy to a rear-mounted 3 phase electric induction motor, in turn driving the rear wheels. The Stir-Lec I had a top speed of 55 mph (89 km/h). While the car is running, the batteries are constantly recharged by a small Stirling engine in the rear. The engine was allegedly so quiet it was hard to determine if it was running or not, just by sound. Since the Stirling is an external combustion engine, the exhaust has virtually no odor and pollution levels can be made very low.
Another hybrid electric car GM experimented with in 1969 was the XP-883 which featured a similar, but reversed drive line to the Stir-Lec I (using front-wheel drive, with a front-mounted motor and engine, along with rear-mounted batteries).