Excellent Information on Motorhome HP Requirements and Fuel Consumption

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Originally Posted by Jon Wehrenberg

You only pay for the horsepower you use. With the exception of more engine weight and higher internal friction in a higher horsepower engine which has a modest impact on fuel economy it is your right foot that regulates your fuel consumption.

If you have a big engine, but choose to climb long steep hills using the performance of a smaller engine you will consume the same volume of fuel as the smaller engine. <<< snip snip snip>>>

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Except that engines seem to acheive their optimal BSFC (brake specific fuel consumption) at their peak torque outputs; consequently, in the above example, the smaller engine will have better fuel economy.

A smaller engine will always have better fuel economy than a large one because of the energy required just to overcome the forces required to operate the drivetrain and overcome friction.

However, if I operated my engine at the peak torque output I would either have to drive around mostly in first gear, or be driving very fast at which wind resistance and other factors would damage my fuel economy.

I short shift as much as practical and get into 6th (or high gear) ASAP which in the case of the Corvette puts me at 60 MPH at 1300 RPM (approximately) significantly below peak torque and HP. Operation at peak torque might be more applicable to a diesel where peak torque is reached at relatively low RPM, such as in our buses, that are mated to a transmission whose shift pattern is set to upshift at relatively low RPM unless we go into performance mode.

Jon, Your 60 mph, 1300 rpm vette brought a grin to my face. In 1967 I had a 67 vette, 427, that turned 3000 rpm's at 60 mph. The auto industry has come a long way !

It would bring tears to your eyes when you had that 427 if a typical hot car of today, such as a Subaru WRX or even an Impala with the V8 ate its lunch in a drag race.

My 63 Corvette would do the 1/4 mile in 14 seconds at 98 mph, something close to what the average car does today. And that car needed points and plugs every 10,000 miles and it ate universal joints on the half shafts at the rate of one every 30,000 miles or so. Today we probably don't even have to change plugs for 100,000 miles and most mechanical stuff lasts far in excess of that. Aaaahhh the bad old days.