Quote:
Originally Posted by Chance
When a small motorhome with a 6.8-liter V10 can get around 10 MPG traveling at an assumed speed of no more than 70 MPH, it means that during steady-state cruising it's only burning fuel at 7 gallons per hour or less. At lower speeds the average fuel burn rate is even lower.
If we work backwards (reverse engineering) it means that the V10 needs to be at fairly low RPMs to be at near maximum efficiency. Anything at much over 2,000 RPMs (in this case) will start to decrease engine efficiency and thus decrease fuel economy. Cruising on level roads at 3,000 to 3,500 RPMs would be too high for such a small fuel-efficient motorhome.
For larger motorhomes that require more power at same vehicle speed, operating at higher RPM may be optimum for that RV. Engine RPM itself is not a very good indicator of engine efficiency. It also has to be weighed against load on engine.
For all practical purposes, most gasoline engines can operate over a wide range of RPMs while maintaining good engine efficiency; but only if the load on engine is appropriate for the RPM in question.
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Chance,
Your figures are right on the money with the mpg that I usually get on a more or less flat terrain considering little to no head winds. I usually try to keep the rpms around 1950-2000 which is around 58-60 mph. That seems to be the sweet spot for my camper. Mostly get 10-11 mpg and mostly closer to 11 and sometimes in the high desert runs over 11 mpg.
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