Don't trust Wikipedia or the DieselShop for accurate info on locos.

The GP38 was introduced about 1965 when EMD introduced the "40 line" and changed from the 567 engine to the 645 engine.

The GP38 uses a 16 cylinder 645 engine that is roots blown. It came standard with a D32 main generator, but as an option could be ordered with the new AR10 traction alternator that was used on the GP40/SD40/SD45/DD40A. The traction alternator on the GP38AC had a much higher capacity and allowed for simpler transition and less maintenance.

While not in the original catalog, there was apparently a request for a model between the 2000 hp GP38 and 3000 hp GP40. EMD responded with the GP39 which used a 12 cylinder 645 engine that was turbocharged for 2300 hp. The AR10 was standard, but some customers requested the D32 instead resulting in the GP39DC.

The GP38 and GP39 use the same frame, cab and carbody. The most obvious difference is having either two or four exhaust stacks over the engine (GP38), or a large single turbo stack on the cab side of the engine (GP39). There should be a slight difference in the engine door arrangement, but I would have to look to confirm. There is no external difference between the D32 and AR10 versions.

Both models were upgraded to the Dash-2 series about 1972 which made the AR10 standard on both models. The GP38-2 had several variations over production in the radiator and frame edge. The GP39-2 had three major changes, with the second phase having the engine and related items moved back on the frame, and the thrid version using the same carbody as the GP49 (which is a GP39-2 upgraded with higher horsepower, D87 traction motors, and an AR15 with Super Series control system).

Other than horsepower rating, the BN/BNSF GP39V-GP39M-GP39E units have nothing to do with the true GP39 model. These are former GP30 and GP35 units that were completely rebuilt with an AR10 and Dash-2 electrical control, but kept their 16 cylinder turbocharged engines derated to 2300 hp.

Because the EMD 567/645/710 engines are two stroke, they must have positive air box pressure to start and run. This can be provided by roots blowers which require a definite part of the engine horsepower to turn them. The EMD turbochargers are actually driven of the engine drive train similar to the blower, but at around Run 6 the exhaust gases alone are sufficient to drive the turbo and an over-running clutch allows the turbo to turn faster than the drive train reducing the need for engine output to be used for this purpose. The turbocharged engine has the advantage of being more fuel efficient at higher throttles and higher altitudes, while the roots blown versions have lower maintenance costs and are more fuel efficient at lower throttles.