The Man
Dave Whitmer of Greenfield, Indiana, is not afraid of a challenge and assigned himself with the task of making a Super Duty into a Super Commuter. He puts more than 35,000 miles on his truck each year while working as a utility engineer at Ball State University and wanted to improve the mileage. Dave is no rookie in the world of diesel technology. He went to work for a diesel locomotive factory right out of high school and has been driving oil-burner trucks since 1983. In fact, Dave was driving a GM truck with an underwhelming 6.2L under the hood before he bought this F-350 in 2000.
The Machine
Now, Dave had the perfect platform to build a fuel-sipping project: a two-wheel-drive truck with a six-speed manual transmission and a 3.73 rear gear set. That's a decent axle ratio for fuel economy, but after some searching, he was able to find a 3.08 ring-and-pinion that would fit inside the differential. It's filled with Amsoil synthetic lube and allows him to cruise at 60 mph at 1,450 rpm (or 70 mph at just 1,700 rpm), which immediately slowed down the needle inside the fuel gauge.
With the engine revs under control, Dave embarked on improving the efficiency of the 7.3L Power Stroke. He added a large aftermarket air filter and a 4-inch exhaust system, then disabled the backpressure valve on the turbo that had caused him to lose about 2 mpg during the winter. He also added a 203-degree thermostat that keeps the engine running hotter than stock, which improved his mileage by three-quarters of a gallon (even more in the winter). The cooling system also had all the water removed and replaced with Evans waterless coolant made of 100 percent propylene glycol. The last drivetrain modification was a custom-burned chip that decreases fueling and advances injection timing under 2,000 rpm to maximize mileage. Above two-grand, the chip switches to its performance mode, which is good for adding 56 hp at the rear wheels.
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The faring over the bed is made of the rubber used to put tread on stairs (with the ridges down). It's held together with fender rivets and stretched over a homemade skeleton made of plywood and 1-inch stock. The slope of the faring is 25 degrees, which is based on findings by NASA and NASCAR (yes, they sometimes work with each other). Aerodynamic tests have shown that a slope steeper than 27 degrees will cause the airflow to separate from the canopy and cause mpg-robbing drag. |  |
The covers over the windshield wipers are designed to keep them from getting packed with snow and ice, but they work well at making this Super Duty slip through the air. | 
The 4-inch DPI exhaust was good for an instant 150-degree drop in the exhaust gas temperature. With all of the modifications, Dave is able to consistently run the truck with a low EGT. Every once in a while, he blasts up a grade to get the temperature up to 1,200 degrees to burn out any built-up coke deposits. Dave would like to lower the truck another couple of inches, but has already snagged the exhaust tip in a parking lot. | 
The F-350 rides on stock aluminum wheels and Firestone Steeltex Radial R4S tires. The rear tires are the stock size at 235/85R16, but the fronts were reduced to 225/75R16 to lower the truck ride height by about 2 inches (in addition to the 3-inch suspension drop). |