F unit Phases

F3 phases

The F3 were built by General Motors' Electro-Motive Division (EMD) in 4 phases between July 1945 and February 1949. with a total of 1,111 A units and 696 B units. All four phases developed 1,500 horsepower per unit.

Dynamic brakes were optional, you can see them by looking at the roof just behing the air horns, 2 rectangular screened openings.

F units were geared from 65 to 102 on gear ratios of 62:15 to 56:21.

Phase I units are distinguished by 3 portholes on each side, all other phase only have 2. Produced from July 1945 to May 1947.

Phase II added added airflow to the engine by adding 4 filtered air intakes between the front and rear portholes, covered with the famous "chicken wire". Early phase II locomotives used high shrouded radiator rans on the roof, late phase II used low profile fans. Early Phase II produced from June 1947 to December 1947. Late Phase II produced from December 1947 to July 1948.

Phase III added louvers to the air intake openings and eliminated the screen wire between portholes. Produced from July 1948 to September 1948.

Phase IV replaced the remaining screen wire that covered the louvers along the top edge of the roof with stainless steel grills. Produced from September 1948 to February 1949.

B units were essentially unchanged from phase I to Phase III, they got the stainless steel grills in Phase IV. 

The F3 served as the precursor for the very successful F7. The F7 is virtually identical to the Phase IV F3's except for adding a roof mounted radiator fan (for dynamic brake cooling?).

F7 and F9 phases

try this link:  http://trainweb.org/jfuhrtrain/CF7frames/F7Phases/F7phase.html