The 1970 240Z was introduced to the American market by Yutaka Katayama, president of Nissan Motors USA operations, widely known as Mr. K. The 1970 through the mid-1971 model year 240Z was referred to as the Series I. These early cars had many subtle but notable features differing from later cars. The most easily visible difference is that these early cars had a chrome "240Z" badge on the sail pillar, and two horizontal vents in the rear hatch below the glass molding providing flow through ventilation. In mid-1971, for the Series II 240Z-cars, the sail pillar emblems were restyled with just the letter "Z" placed in a circular vented emblem, and the vents were eliminated from the hatch panel of the car. Design changes for the U.S. model 240Z occurred throughout production, including interior modifications for the 1972 model year, and a change in the location of the bumper over-riders, as well as the addition of some emission control devices and the adoption of a new style of emissions reducing carburetors for the 1973 model year.
Source: Wikipedia (original)