Ethyl gasoline Thomas Midgley, a GM research scientist, discovered that blending tetra-ethyl lead with gasoline helped reduce combustion detonation -- commonly known as engine knock. The advance allowed higher compression ratios to be used in the development of more powerful engines and ethyl gasoline was introduced to the public in 1923. Closed bodies In the early days of motoring, the 'horseless carriage' was nothing more than an open platform. Cadillac was the first automaker to offer closed bodies -- on the 1906 Osceola concept -- preventing rocks and debris from battering motorists. Over the next decade, Cadillac and other auto companies embraced closed passenger cabins, and allowed driving to become a less rigorous activity. Crank case ventilation In the early days of motoring, engine parts became corroded from a mixture of sulfur in gasoline with air and vapor under the hood. In 1928, GM researchers placed vents in the crank case, introducing fresh air to the engine, and allowing vapor to escape and helping to reduce most corrosion. At the time, oil was changed every 500 miles on average; the ventilation extended that to 2,000 miles. Two-cycle diesel engine Under Charles 'Boss' Kettering's leadership, GM Research developed a revolutionary two-stroke diesel engine that was smaller, lighter, more powerful and more efficient than traditional diesel engines. It weighed one-fifth as much as a four-cylinder diesel but produced the same amount of power. Within a few years of its 1933 debut, it was being applied to railroad locomotives, boats and off-road equipment. Automatic transmission In 1940, the first completely automatic transmission debuted on Oldsmobile models. A fluid coupling and an automatic planetary geared transmission was operated through a hydraulic pressure control system. In another industry first, by 1954 GM was offering the Hydra-matic automatic transmission on every size GMC truck . PCV In the 1950s, GM researchers first identified engine blow-by gas as a major source of hydrocarbon emissions. To cap the leak, they created the 'positive crank case ventilation' system -- now known as the PCV valve. It was made standard on all GM cars starting in 1963. Safer steering column The energy-absorbing steering column was a significant safety development by GM and was first installed on all GM cars in 1967. It featured a break-away instrument panel attachment, and telescoping shifter tube and steering shaft. It helped reduced the force of impact when a driver was in a severe frontal collision. Catalytic converter The catalytic converter was an important advance toward the elimination of automotive air pollution. Developed by GM researchers starting in the 1960s, it uses platinum as a catalyst to burn any hydrocarbons before they are released into the atmosphere. GM made the technology available to other automakers at no cost. Space guidance systems NASA tapped GM's AC Electronics division in the 1960s. Inertial guidance was the first form of navigation to rely on no signals, no familiar landmarks, no stars or planets. GM developed and delivered the navigation systems for the entire Apollo moon program as well systems for the Lunar Roving Vehicle that the Apollo 15 astronauts first drove on the moon in 1971. EV1 Introduced in 1996 and discontinued in 1999, the EV1 was the first battery electric-powered vehicle to be marketed in the United States in modern times. It used advanced battery technology and GM's second-generation electric drive system to achieve improved range and performance. Plug-in electric vehicle The Chevrolet Volt -- a so-called series-type hybrid electric vehicle -- is introduced, bringing plug-in electric vehicle technology into public focus. It is designed to use a common 110--volt household plug and engineered for someone who drives less than 40 miles a day. For longer trips, the Volt's engine kicks in to recharge the lithium-ion battery pack as required. In 2008, GM tapped several suppliers to intensify development of lithium-ion batteries for the Volt, which is expected to debut in 2010.