engine rpm for mph

[shaper2005]

I have 1999 7.3 F-350 I have not owned this truck for long and I due see on this forum a lot of issues with fuel milage and mine is no different. I assume that my truck is pretty much stock as far as transmission and rear end gearing is concerned. I am trying to find out what the normal RPM range is for driving down the interstate. Right now if I go 70 I am running between 2200 and 2300 rpm. I talked to one guy who told me he his truck is running less then 2000 rpm for that speed. I do not have any codes and I am trying to figure this out because the truck does not seem to have any power in reserve. Any information on rpm ranges might help me to see if i have a problem or if this is typical of this engine.

thanks

[r_marczak_83]

Tire size could be a factor. If he has larger tires his RPM's will be lower at a given speed than yours with factory or smaller ones.

[jimmyp]

I run a 285's and a 6sp, At 70mph, im running right at 2100rpm. Also you and your buddy may also have different ring and pinion, 3.73s vs. 4.10s. "stock" gearing is a little vague.
Jim

[01powestroke]

he could have lower gears then you, our truck runs about 2100-2200 at 70

[dmd]

3.73 gears will run at 2000 rpm at 68 MPH, you probably have 4.10's. With those
gears you will never get good milage. Staying under 2000 RPM will get you
the best milage. Drive 65 MPH and get better(with 3.73's), drive 60 and get even better. With 3.73's you can get over 20MPG if you drive 60 or less.... But only those that have
lots of time will get that milage (or if you calculate it going mostly down hill)

[shaper2005]

Thanks guys Is there a way to find out which gears you have without opening up the rear end?

[SuperCrutyPS]

There should be a tag on the differential unless the gears were changed and it was left off.