"The first thing you'll need to know is that a supercharger and a turbocharger are pretty much the same thing. Both are essentially air pumps, cramming more air into the intake than an engine can suck in on its own. Boost, which is normally measured in pounds per square inch (psi) or bar (1 bar = 14.7psi), is the amount of air pressure that an engine will see over a naturally aspirated setup. The difference between the two chargers lies in the fact that turbochargers make boost through the spinning of a turbine wheel that is pushed by exhaust gases, while supercharger compressors are driven by a belt connected to the various pulleys on an engine's face."
Read more:
http://www.importtuner.com/tech/0609_im ... z2SWrVLxhCNow that we have that all settled my question which I still don't know is the 645 in the GP38-2 just plain normally aspirated (no boost of any kind) or does it have some sort of pressure boost on the intake?
I know wikipedia is not always accurate but it says:"The GP38-2 differs externally from the earlier GP38 only in minor details. Its most distinctive identifying feature is the cooling water level sight glass on the right side of the long hood. The battery box covers of the Dash 2s are bolted down instead of hinged. It can be distinguished from the contemporary GP39-2 and GP40-2 in that its Roots blown engine had two exhaust stacks, one on each side of the dynamic brake fan,"
Again from wiki: "Rebuilds
A number of higher horsepower 40 Series locomotives have been rebuilt into the equivalent of a GP38-2, by removal of the turbocharger and the substitution of twin Roots blowers."
Which would indicate that the GP38-2 was supercharged not turbocharged.