So I got to go on a little road trip yesterday. Totaled 493 miles. Probably 90% highway driving. Mileage came in at 16.04 mpg Vehicle is an '88 E250 with a c6 and 3.54 gears. Cruise control set at 67mph with the a/c running 75% of the time.

Van ran perfectly the whole time and over all I am happy with the mileage. Wanted to use this as a shake down run prior to our 2200 mile trip in September. Better to have something break now when I have time to fix it rather than when we are half way to Flordia with the kids in tow. I am sure if I slowed it down to about 60mph I would see an increase in the mileage. A fresh air filter and oil change may have helped some (at the end of the trip I was 35 miles over for my next oil change). Should have checked the the tire pressure before I left for the trip, but I was running out the door. Checked it after the trip and I was at 70psi with hot tires. An increase to 80psi cold may help reduce the rolling resistance some.

The trip was to go pick this up. It should help a little with the mileage as well.

 

It will be interesting to see what you get for mileage with the van and the DNE2 with 3.54 gears. You should be just a little shorter than my truck in Double OD, so im interested in seeing if you see any gains. I don't see any gains in double OD.

 

Cruising at 65mph it should drop my RPM's from 2673 to 2139 (according to my math). With mine being a stock non-turbo 7.3 it should get me closer to cruising at my 1800 rpm torque peak. Hoping this will increase the engine efficiency to allow less fuel usage.

 

Your RPM's are that high? Must have some small tires on that thing...

My truck with 35's is right at 2K in single OD with 4.10's at 60mph...

Final drive with 4.10's is 3.44 compared to your 3.54.

Double OD puts me at 2.75 final drive, and 2.83 for you with the DNE2.

At 60 in double OD Im between 1600-1700 RPM.

Are you sure you have 3.54's?

 

Pretty sure.

I just used a gear calculator app on my phone. It is possible that I put the information in wrong. I went out and measured my tires since the calculator uses tire height. IIRC mine were 29". Speed 60mph, Diff ratio 3.54, trans gear ratio .8 (w o/d engaged). RPM's come out to 1974 at 60mph.

I think it is correct since when I put your numbers in I came up with your RPM's being 1588 at 60mph.

 

Wow yeah, I figured you had taller tires, lol...