Even more amazing to me is the fact that modern engines are simultaneously more powerful and much more fuel efficient than the muscle car era engines. In the 1970's the only cars which could achieve 30+ MPG were the little Toyota and Honda economy cars with their tiny engines. We would be hard pressed to find a 1970's car with 300+ HP which could also achieve over 12 MPG on the highway.
part of the increase in mileage can be attributed to improvements in transmissions .... in the '70's most automatic transmissions had 4 speeds .... our '11 Chevy truck has 6 and the new Camaro has 8