 An identification detail of the GP20 is the small radiator fan added ahead of the large aft fan.De-turbo-ed GP20s, which employ 645 power assemblies, with Roots blowers replacing the EMD turbocharger without de-rating the horsepower of the locomotive, are somewhat common.As the reliability of the EMD turbocharger significantly improved over time, these de-turbo-ed examples became less common.