Production of 600hp units began in 1932, in 1934 the car body was refined by Otto Kuhler. The resulting
"High Hood" body style lead to the commonly used model designation, HH. In 1937 the 531 engine was
turbo charged to increase horsepower, the HH900. Application of the 539 engine resulted in the 660hp
HH660 and the 1000hp HH1000 models.|
Changes in the car body configuration, (steps, louvers etc.) did not correspond with the switch to the 539
engines in 1939. In 1938 staircase steps replaced ladder steps then engine hood louvers replaced flaps.
The result is that later HH600 and HH900 models look the same as HH660 and HH1000 models.