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[Anonymous]

Why are the radiators flared on these to locomotives and what is the difference between the SD40 and the SD40X?[:D]

[nanaimo73]

There were 4 SD40X built in 1979 for KCS. These were a SD50 built on a SD40-2 frame. Next came 6 SD50S for Norfolk and Western, and these were also 68'10'' instead of the normal 71'2'' for a SD50. Both groups had flat radiators.
There was a GP40X built in 1965 that was a prototype GP40.
Then there were 23 GP40X with flared radiators, built in 1977 and 1978. ATSF got 10, Southern got 3, Southern Pacific got 4 and Union Pacific got 6. UP and SP came with HT-B trucks while SRR and ATSF got Blomberg M trucks. Some of these have just been rebuilt for Canadian Pacific.

[CSSHEGEWISCH]

There were also nine SD40X's built as testbeds for the 645 engine, EMD 434 and 434A through 434H. 434A through 434F had flared radiators, the others had flat radiators. 434 became GM&O 950 and 434A-434H became UP 3040-3047.

These locomotives plus GP40X 433A were pre-production prototypes for the 645 line of locomotives which was introduced in 1965 and went to production in 1966.