Looks like it may be time for a refresher on the terms "supercharged" and "Turbocharged" when discussing EMD diesel prime movers:
1) Since the EMD/GM diesel engine was and is still a two stroke cycle, any and ALL air for combustion MUST be "forced" into the combustion chambers (there is NO intake stroke). Thus ALL 567 and 645 engines, generally classified throughout the industry as "normally aspirated", where in fact SUPERCHARGED.
2) Beginning with the "special" experimental GP9 units on the Union Pacific, way back in the mid to late 1950s, which where the very first "turbocharged" EMD 567 engines, EMD was forced to drastically increase the air pressure for combustion. Thus the GP20 and SD24 locomotives where born with the first production "turbocharged" EMD two stroke cycle diesel engines.
In conclusion, EVERY single EMD two stroke cycle diesel engine is either "supercharged" or "turbocharged", depending on the locomotive model. Otherwise the two stroke cycle EMD diesel engine would not even start without a roots blower or a specially designed turbocharger with an over-running clutch in its internal drive gear train.
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