Up front, let me say that I am by no means an expert on this subject. I understand that de-turboing, or replacing the turbo charger with two roots blowers, is a major job because the gear train on the end of the engine block is quite different for the roots blowers vs the turbo charged block.

I believe that an engine can be de-rated by tweeking with the governor settings. I don't know what settings or how involved this is. An example is BNSF 6324. Originally built as a straight SSD-40, it is now a belt pack remote unit, derated some but still retaining its turbo charger.

Another interesting derated loco is the one I run for Western Rail Switching here in the Spokane WA area. A GP-30 built as C&NW 920, it migrated to Fox River Valley before becoming WC 2253. Western Rail replaced the original 16-567-D1 turbo charged block rated at 2250 hp with a 16-567-C roots blown engine rated at 1800 hp. It is a great running engine with one of the sweetest sounding 567s I have ever heard. It also retains that great GP-30 carbody that railfans love. From my point of view, I love the roomy GP-30 cab and the AAR control stand.



Now, I realize that I am drifting off topic somewhat. Here is a link to a 26 second recording I made of the diesel engine in 2253 being started:

WRS 2253 being started

If you browse YouTube a bit, you can find some interesting videos from across the pond. Here is one that I enjoyed. They must have very stout batteries!
D5600 Cold-start

Bruce Butler