How is it that a 5.9 cummins can have a higher toque to horse power ratio in some apllications than others.what do they do to the electronic and mechanical engines to change them. For example in some applications the engine might have low horse power but a ton of torque and in other applications the engine might have a high horsepower rating but a lower torque trating

 

It all has to do with, at what RPM the peak HP was developed. The lower RPM the hp peaks at, the higher the TQ.

These are some general numbers to look at.
HPx5252/RPM=TQ

180HP @1600RPM = 590TQ

180HP @2500RPM = 378TQ

400HP @6000RPM = 350TQ

349HP @2055RPM = 900TQ Thats mine

See why diesels have so much TQ? Low RPM HP. Cant beat it.

 

The other thing that's really common now with the electronic diesels in heavy applications is high torque rise ratings. Torque rise is the percentage of peak torque that is available at peak HP. High torque rise engines have less torque at peak HP (which means peak HP is lower). Basically what that means is that the engine is programmed for low HP on purpose to "encourage" the driver to shift early for better fuel economy. The high torque rise rating will have the same torque as a low torque rise rating but less HP. They aren't much fun to drive, they don't pull any harder as you wind them up - I guess the best way to describe them is they feel "flat".