Building A Jeep To Drive
It is an accepted fact that the more built a Jeep is, the worse the gas mileage gets. Often we build our Jeeps up to do so well off-road that we can't justify the cost at the pump of driving them on-road anymore and end up buying a second vehicle to drive day to day while the Jeep sits languishing by the side of the house.
We recently bought this '98 Cherokee for $1,000 to drive back and forth to work. It has the 4.0L, AW4 automatic transmission, and NP242 transfer case, and we quickly fell in love with being able to get 340 miles out of 18-19 gallons of fuel. It turns out that for a Jeep, a stock Cherokee gets great gas mileage.
The problem was that because of the mileage the Cherokee got, we kept taking it places and wheeling it, which, since it had no skidplates, a low-slung stance, and other stock-Jeep limitations, meant there was always a trail or obstacle impassable to our stock XJ without damage. We got to thinking: What if we could build this Cherokee to do better off-road, while at the same time retain its on-road manners and mileage? Thus Project Mileage Master was born.
We are going to take a two-pronged attack to achieve our goals. We are going to add all the stuff that an off-highway Jeep needs, such as lockers, armor, a lift, more aggressive tires, recovery equipment, and the like. All this stuff adds weight, can affect efficiency, and can lead to increased fuel consumption through added drag, friction, and rolling resistance. So, we are going to keep an eye on what stuff weighs as we add it and see how it affects fuel economy.
The other side of the equation is that we think if we can increase the power output of the engine and increase efficiency of the drivetrain overall, then by putting more power to the ground for the same amount of fuel consumed we can possibly actually increase the mileage of the Jeep as we go. So, we are going to be testing power adders and for each one note what change in mileage there was, if any. After each modification we make in an effort to get more power, we will dyno it for real-world test results on each modification.
After each change, we are going to put at least a thousand miles on it-but in most cases 2,000 or more miles-and calculate the average fuel economy as we go.
Even if you don't have an XJ, a lot of the things we discover along the way will help you in building your Jeep to become a better wheeling machine while not breaking the bank every time you pull up to a gas pump.