Torque curve?
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I'm sure Cummins has one but I haven't see it. I've seen the one for its predecessor, the 4bt 3.9 so it's logical there is one. Have to be specific. There is an ISB170 3.9 engine and an ISB170-40 which is a 5.9 6bt. Might contact member CrewCab59 and see if he has a sheet on that engine. He is a Cummins dealer.
Here is a picture of the torque limit in the ecu. It seems to follow it pretty closely, but idk how accurate it is.
Those torque numbers look pretty normal for a Cummins. Hits a peak around 1600-1700 RPM and starts to drop significantly after 2000 RPM. Factory specs on the ISB3.9-170 show 420 lb ft @ 1600 RPM which is exactly what you have there. Peak 170 HP comes at 2300 RPM.
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