[Big Dave]

I must certainly be fun squeezing extra MPG out of a Prius or Insight, but the bigger challenge is getting decent mileage out of the most indecent of all. The Excursion and the Hummer H2.

The (now discontinued) Excursion is nothing more than a Ford Super Duty truck chassis with a station wagon body. Most are diesels. After 2003, all use the 6.0 (IH T366) diesels where the earlier ones use the 7.3 (IH T444) engine. All Excursions come with an automatic transmission. Most are 4x4 but about 25% were 4x2. A 4x2 diesel Ex gets roughly 14 MPG in mixed driving. I could latch onto a 2002 4x2 Ex for about $20,000.

What would be my plan? First a big dose of drivetrain mods. Put the numerically lowest gearing I could find in it. For a 4x4 that means swapping the stock 3.73s for 3.55s. for a 4x2 with the 10.25” Sterling axle I could get 3.08s. Second, I do the “sex change operation” and install a manual transmission. My SD uses a ZF6-650 which has a 0.72:1 overdrive and is built to last forever. In the case of the 4x4 I need more overdrive, so I go to the Tremec T-56 “Viper” transmission. It can take the tremendous torque of the International engines. Then I do some aero mods. If the vehicle is a 4x2 I can slam it 3 inches in front and 6inches in the rear. (No slamming a 4x4, though) This reduces ride height and apparent frontal area. An air dam, side skirts and rear fender skirts and maybe some grille blocking (I’m working on a grille block for my SD). Install a pyrometer to provide EFT guidance for the driver. Maybe I add a digital tach. Maybe altogether I have put an additional $7000 in the vehicle.
MPG Improvements
Regearing: 2.5 MPG for 4x2 1.75 for 4x4
Manual transmission: 2 MPG
Aero mods: 2.5 MPG for the 4x2 1.9 MPG for the 4x4.

Total: 7 MPG (50%) for the 4x2 5.65 MPG (40%)

Not gonna make the Prius engineers lose sleep, but not bad.


The H2 is nothing more than a Chevy Silverado half-ton truck chassis with a tarted-up station wagon body. All use either the 6.0 or 6.2 liter variants of the updated small-block. All H2s come with an automatic transmission. All H2s are 4x4. A H2 gets about 11 MPG in mixed driving. Despite all, the Hummer remains an expensive used car. It is tough to find one under $35,000.

For the H2 my plan starts with losing the gas-pig engine and the frail and inefficient automatic. A Cummins 4BT3.9 four-banger would fit nicely into that deep engine bay and accessory drive parts are available off the shelf. Alternately, a 6.5 Hummer turbo-diesel is a bolt-up. I mate it to a T-56 out of a Camaro. That variant of the T-56 has a huge 0.5:1 overdrive. That big overdrive ratio obviates the need to replace the 3.73 gears in the Hummer. You can’t slam a 4x4 and the Hummer sits so high that beyond maybe some grille blockage and rear fender skirts, you really cannot do much from the aerodynamic standpoint. I include a pyrometer and a digital tach. I have about $8,500 in the mods over and above the cost of acquiring the vehicle.

MPG Improvements

Diesel engine: 4.5 MPG
Manual transmission: 2.5 MPG
Aero mods: 1.0 MPG

Total: 8.0 MPG (73%)

Getting a H2 to 19 MPG would be nothing to sneeze at.