Mission Impossible: Taming the Giants (Excursion/Hummer modding)

[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.

[tasdrouille]

Those vehicles shouldn't even exist. There is nothing to justify their existence except the ego of their owners.

[bhazard]

^^^ Im with those guys. Sorry.

I could MAYBE see the excursion as a tow rig that can also haul people/cargo. But thats it. I despise people that daily drive those sorts of vehicles.

[Ryland]

It would be a fun pit to toss money at... just to show people up who drive those things, but they are an all around poorly designed vehicle, for hauling people you are almost better off with a small school bus! about the same kind of mileage, and way more space, for hauling cargo... same thing, or small van, hell, the freghtliner vans can do more and get better mileage.

[Silveredwings]

I was going to say that nobody ever lost money betting on the wastefulness of Americans ... but then I realize that GM has set new records doing so. Ford is right behind them. Maybe there is hope.

[LostCause]

I think it's an interesting mental exercise. Maybe not for a grocery-getting 19mpg Excursion, but for their close cousin: the Humvee...the evil that started it all...

How could Humvees be modified to return better mileage. I bet 90% of the time they are just tooling around the desert, with the rest spent smashing down gates and outrunning terrorist potshots. I believe the military would be heavily interested in fuel efficiency...it lessens the logistics of supply convoys.

I'm thinking high psi tires, overdrive transmission, regeared axles, TDI (if it isn't already implemented), curved body panels (which would probably help deflect bullets/shrapnel), and a severe weight cutting regimen (kevlar instead of steel?)...

Composite HMMWV


- LostCause

[johnpr]

what steel panels??? the humvees are made from aluminum with a fiberglass nose, unless your talking about the armor packages, at which point you have steel panels but eh it doesnt really matter to much now, we are looking at new vehicles for the military (yep the humvee is becoming obsolete) as for high pressure tires, they have a inflation system, with the press of a button you can switch the pressure for whatever terrain your on. honestly there isnt much wrong with the humvee other than the people who thought they would make great daily drivers..... they were never intended to be road vehicles....

/rant

[johnpr]

just for a note, dont take my rant as attacking anyone, it just annoys me that people wanted to drive around in a "military" vehicle so bad that they became a production vehicles, there are just some things that people should just say hey thats cool, and leave it at that.

just my .02

[Silveredwings]

johnpr is right about the HMMMMV. Even the fuel tank is plastic. As far as reducing their FE, the Army was toying with a hybrid system that could be used in EV mode for stealth.

[LostCause]

I'll do research on my own, but does anyone have any idea what the HMMWV is going to be replaced with? I remember seeing potential replacements awhile ago, but they seemed pretty deep in the conceptual realm at that time.

Good point about the fiberglass body-panels, I hadn't thought about that. I bet the frame/chassis still weighs several tons on that thing, though.

I realize that the military has more important things to do, but it's mildly annoying to see the total disregard for pollution control/frugality. I guess that's one reason to be a pacifist.

B-52 Synthetic Fuel Test


- LostCause