thus complementing the 3rd generation 137 hp AC Induction electric motor installed in the hood. Hybrid modifications retained the capability of all-electric ZEV propulsion for up to . EV1 CNG The compressed natural gas (CNG) variant was the only non-electric vehicle in the line-up, even though it employed the same up-stretched platform. It used a modified Suzuki G10T 1.0 liter turbocharged 3-cylinder all-aluminum OHC engine installed under the hood. Due to the high octane rating of the CNG (allowing for a greater compression ratio), this small engine was able to deliver at 5500 rpm. The batteries were replaced with two CNG tanks capable of maximum operating pressure of 3000 psi. The tanks could be refueled from a single nozzle in only 4 minutes. In-tank solenoids shut off the fuel during refueling and engine idle, and a pressure relief device safeguarded against excessive temperature and pressure. With the help of a continuously variable transmission, the car accelerated in 11 seconds. The maximum range was , and fuel economy was in gasoline equivalent. EV1 series hybrid The series hybrid prototype had a gas turbine engine APU placed in the trunk. A single-stage, single-shaft, recuperated gas turbine unit with a high-speed permanent-magnet AC generator was provided by Williams International; it weighed , measured in diameter by long and was running between 100,000 and 140,000 rpm. The turbine could run on a number of high-octane alternative fuels, from octane-boosted gasoline to compressed natural gas. The APU started automatically when the battery charge dropped below 40% and delivered of electrical power, sufficient to simultaneously sustain the EV1's 80 mph top speed whilst returning the car's 44 NiMH cells to (and maintain them at) a 50% charge level. A fuel tank capacity of and fuel economy of to in hybrid mode, depending on the driving conditions, allowed for a highway range of more than . The car accelerated to in 9 seconds. There was also a research program that powered the series hybrid Gen2 version from a Stirling engine-based generator. The program demonstrated the technical feasibility of such a drive train, but it was concluded that commercial viability was out of reach at that time. EV1 parallel hybrid The parallel hybrid variant featured a de-stroked 1.3 L turbocharged DTI diesel engine (Isuzu Circle L), delivering , installed in the trunk along with an additional DC motor/generator; the two motors drove the rear wheels through an electronically