Mr. Pwragn,
I don't think any one is saying your lying or stupid. My self I'm rather dense. So I fail to see how using more fuel to turn more RPM's which would seem to make your engine work harder can save fuel. I have always been under impression the lower RPM's the less strain\stress on the engine.
All other factors being equal, you're absolutely right. But not all other factors are equal.
The issue here, is that for emissions purposes, this thing is very detuned. Given the weight and size, it should easily do 30-35 mpg at 55 mph. But it doesn't. It gets a whopping 21-23. But the detuning for emissions purposes is not nearly as bad at 2400 as it as it 1750 - 1800.
So, while you're pushing a LOT more horsepower because you're moving the rig faster, it's just running vastly more efficiently.
For 13 years, I was a diesel injection specialist for many brands of diesel injection systems, factory certified in one. I did original research for economy and performance improvements when the Dodge w/Cummins came out for the aftermarket. Customers began to tell us that when we turned things up, and they went faster, it took less fuel to get from point A to point B. So, we investigated and experimented.
I did a lot of studying engine theory and just flat out trying "stuff". We often saw modified trucks that would take the exact same amount of fuel to move the owner's travel trailer down the highway at 65, as the unmodified and empty truck following them. These are extreme examples, to be sure, but they are neither unusual nor rare. When the electronic systems came out and people could simply experiment with new settings, it became more and more apparent that automakers are often giving away 10 to 35% of their fuel economy (and it's worse now than than) to meet emissions rules.
People seem to be under the totally erroneous impression that emissions standards improve fuel economy. Nothing could be further from the truth. Technology has improved economy, but emissions regulations continue to take larger and larger bites into economy.
ANY diesel vehicle produced today, if emissions regulations were relaxed, could get anywhere from 10 to 40% economy improvement - it is dependent upon engine design, which compromises were made during development and testing, what strategy is used to achieve compliance, and to a degree, load and speed.
That my jeep gets about 60% of the possible fuel economy it should at 55 and about 85% at 75 is neither surprising to me, nor all that unexpected. It is, to me, simply exasperating.
