Motor Overload - Trains Magazine

BaltACD

I doubt diesel engine in railroad use are 'tuned' to produce maximum horsepower and/or torque.  The fuel delivery and other operating parameters are designed for the engine to develop the rated output for each throttle notch. 

There are examples where diesel prime movers have been 'tweaked' to make more power and longevity has suffered as a result.  With medium-speed engines like the 7FDL or 567/645 this is done with additional Run 8 speed, and what look like very small speed changes can have colossal effects 'too far'.

These engines are also replete with various critical speeds, where damaging resonance in one component or system or other might develop.  These are well-known and reasonably well documented, and are (as mentioned) an important reason for the relay-logic 8-bit speed-determined MU arrangement rather than a continuous stepless servo like a model railroader's speed pot...

Look in the SAE paper on the development of the 567 -- I believe there is a chart there showing all the critical speeds and notes about what produce them.