Previous Union Pacific experiments with turbocharging had utilized multiple Elliot[REF] or Garrett AiResearch turbochargers feeding the usual pair of Roots blowers.
The introduction of the EMD-type turbocharger was successful and all subsequent GP series were offered with this turbocharger, although not all models within a series were offered with turbocharging (e.g., the 38 sub-models within the 40 Series were Roots-blown).