Fuel Economy Update for the 1993 Diesel Conversion Suburban

[Edahall]

My daily driver is my 82 C10 Shortwide 6.2L stock (except non-egr now).

It's a 2.73 geard truck, but with 26" tall tires because it's lowered 6".

I run 80MPH down the highway routinely and it still returns 27mpg.

J

I did some calculations on RPM vs speed on your truck assuming you have 2.73 gears, 26" tires and 700r4 transmission.

mph vs. RPM
55 - 1358
65 - 1605
70 - 1729
80 - 1976

Then I calculated the RPM's on my 1982 Suburban with 3.08 gears, 30" tires and 700r4 transmission

55 - 1328
65 - 1570
70 - 1690
80 - 1932

It appears that your RPM's are very similar to mine. However, mine does not get as good fuel economy as yours at 80 mph. The lower stance is probably responsible for this. Anyways, it's good to know that lowering these trucks really helps with fuel economy at highway speeds. That said, I may end up dropping my 99 Tahoe that I intend to repower.

[argo]

I forgot to account for the 1.5% error that my speedometer has. The correct average fuel economy is a bit lower, at 24.596 MPG. According to my GPS, I am going 54.2MPH when I am reading 55 MPH on the Speedo. That checks out because I am also going 59.1 MPH when I am reading 60 MPH.

[argo]

I did some calculations on RPM vs speed on your truck assuming you have 2.73 gears, 26" tires and 700r4 transmission.

mph vs. RPM
55 - 1358
65 - 1605
70 - 1729
80 - 1976

Then I calculated the RPM's on my 1982 Suburban with 3.08 gears, 30" tires and 700r4 transmission

55 - 1328
65 - 1570
70 - 1690
80 - 1932

It appears that your RPM's are very similar to mine. However, mine does not get as good fuel economy as yours at 80 mph. The lower stance is probably responsible for this. Anyways, it's good to know that lowering these trucks really helps with fuel economy at highway speeds. That said, I may end up dropping my 99 Tahoe that I intend to repower.

Does your Suburban have a roof rack? That will put allot of drag on it.

[Edahall]

Does your Suburban have a roof rack? That will put allot of drag on it.

It has no roof rack on it. It's just a big old boxy vehicle with the aerodynamics of a piece of plywood held upright.

[john8662]

Edahall,

Seems to help. I got the truck that way (lowered) so it's been an experiment. It seems to get around the same fuel economy at 70 as it does 80. I don't use the A/C because it doesn't work, so I know that helps a bunch.