So I got to wondering while cruising at about 55 doing 1600 rpm....

Rpm versus rate of fuel used versus speed....

Why are there not ratings of gallons per hour used at rpm's...

I was cruising today and for awhile I was doing 60 at about 1750, and then due to some road conditions slowed down to about 55 doing about 1600 rpm....

Now some math would be interesting to do comparing the fuel usage at 1750 rpm versus the usage at 1600 rpm... Now would the extra mpg be worth the slower speed? and vice versa....

I would be willing to contribute some money and time come summer and run a few full tanks down to empty at various speeds....

I think we all might be surprised at the distance/mpg achieved at 55 compared to 60 compared 65 compared to 70 compared to 75....Those are the general speeds most people run depeding on state, load, and speed limit, and conditions....

 

There is quite a bit of difference, thus the reason Carter mandated the 55mph law nation wide back in the '70s. Calculations have been done for years comparing RPMs to MPG, just in the marine industry. I can say the ONLY time I've ever seen 20 mpg on my Blazer was on a long stretch of highway somewhere through the Carolinas with a max speed limit of 55mph.

 

The EPA considers highway speed to be from 47MPH to 52MPH. Above and below that speed fuel economy drops. The EPA recently changed the guidelines for testing bringing the window sticker mileage down closer to what the average driver MIGHT expect to get. The "sweet spot" is still somewhere between 47 & 52 depending on the vehicle.

 

weak....

it might be worth trying that for 3 concurrent fill ups and see if my MPGs improve and how much....