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Dt400 Series Torque Curve

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I have a engine design theory question - I have been logging a fair bit of time on the road for work; it’s left my mind with spare time to wonder and pontificate!

First off - my intent is not to start an IH vs Case “which is better discussion” debate -  I don’t want to start and brand war.  We loved both tractors mentioned below and they each had their pluses and minuses.  My observations below are completely subjective and believe it or not, my “gut feelings” have been proved wrong before!

I grew up on a grain farm, and when I was young we had a 2590 and a 1586 as main field tractors.  At full rated RPM, the 1586 didn’t feel too far away at all from the 2590 in terms of power. The 2590 did seem to be an overachiever on the dyno from factory though - it seemed to always do 195 on the dyno when it was in the shop.  

The difference really showed at the RPM levels - the IH would really light up around 1800rpm, almost where the Case started to fall off.  The torque at 1500rpm on these two engines wasn’t even comparable.  A neighbor had a 5488, and the difference was less, but it still didn’t have near the low end grunt the Case had.  But on pull-type 1482’s in the same field that 5488 had a ton of power (as much or more than the Case) at it’s rated rpm. 

I finished building an only F700 Mercury truck with a DT466 transplant, and I am once again reminded of those DT’s - it really doesn’t light up at all until 1800, and then comes on like a freight train. It’s got the never MW inline pump.

My question is - what makes these two engines so much different is power curves?  The crank stroke on the Case is a bit longer (10%ish).  The displacement is about 10% more... 

Are the cams fundamentally different?

Is the main difference only in fuel pump settings?

Are their reasons the DT can’t handle these lower rpm torque figures?  It seems like the DT is a stout engine.  Are the blocks, cranks or heads not up to the task vs say a 504 Case or 505 Cummins? 

What was IH’s idea with higher rpm?  It seems like high rpm was an IH philosophy?

Another example of this were the old Mack’s - a 300hp 673cube Mack engine seemed to have more bottom end torque than a 350hp 855 Cummins.  I also heard the Cummins wouldn’t last being lugged and they did seem to like rpm.
Those old Mack’s were pretty much done by 1800rpm where the power seemed to just fall off quickly.  The old Cummins was just starting to party at 1600 rpm - they pulled hard to 2100.  What made these two engines characteristics so much differnent?





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