B39-8

Does Union Pacific own B39-8s or B40-8s? The only B-B -8s inherited by the Union Pacific are B39-8s. So did Union Pacific upgrade their B39-8s to B40-8 specifications?

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They are technically B40-8's now. The original SP units where delivered as B39-8's and the Cotton Belt units where delivered as B40-8's. After the CB units where delivered GE updated the software to make them B40-8's.

Was the re-rating just software, or were the units given new turbochargers?