http://www.escortfocus.com/html/mileage_build-up.html
"* A race type 45% underdrive crank pulley was added to cut down on the accessories drag and power loss on the engine. On another Escort we recorded almost a 15% increase in fuel economy. The car would constantly get 40-50 miles more on a tank of fuel with no other changes. "
"The mileage test run was about 200 miles using premium fuel with about 90% highway and 10% stop and go driving coming back through a few small towns on a 2 lane road.
The results was nearly 49 mpg at 60 mph (with the cruise set) on the highway with 2 people in the car.
We run our mileage tests using premium fuel with the tank topped off until fuel is visible in the neck and all the air has been shook out. Then at the end of the test, we refuel at the same pump, same spot, and refill it again. We also try to do test in 45-55 degree temperatures to prevent the gas from expanding in the tank and giving a false reading. The A/C was off and the windows were up.
With the same modifications we took the car on a trip to Florida. Running at an average 75-80 mph (but otherwise driving easy) with 2 people, luggage, tools, cooler, and other assorted items, (over 500 lbs of weight altogether w/passengers). Keeping the air off, but otherwise driving normally we got slightly over 41 mpg on one 300 mile leg of the trip and a bit over 40 mpg on another. How you drive drastically affects mileage. In other vehicles, I've seen at least a 30% drop in fuel economy just by driving habits.
Also this car was over 2 full seconds quicker from 0-60 mph than when it was stock."