American Streamlined Cars Peaked in 1920, MPG peaked in 1950's
Gas Plasma Engine: a new type of energy source is touted as the vehicle's soon-to-come power drive: "This engine is a closed two-cycle reciprocating engine that has no intake, uses no air, emitting no exhaust at all! The fuel is self-contained and hermetically sealed in the cylinders which are initially charged at the time of manufacturing, carrying their own power supply that will last approximately 60 to 75 thousand miles with no fall of efficiency."
An environmentally safe engine that doesn't need refueling for 60,000 miles - Source and further reading: PopCult Mag
Possibly the very first streamlined car - its coefficient of drag was only 0.28
Another aerodynamic oddity, mostly forgotten today - "Rumpler Tropfenwagen"
"Rumpler Tropfenwagen" in Motor show in Berlin in 1921. (Wikipedia article)
Read full with mind candy at DarkRoasted