When computing gas milage figures, one has good accuracy in knowing the amount of distance traveled (if the speedo gear is correct -can be field checked by matching several milage markers along interstates). The other accurate item is how much gas we put into the tank at each fill-up (the gov'mt and interstate regulators keep the gas pumps up to snuff). But taking the milage and dividing it by the volume of gas purchased is not true gas milage. It is just that a ratio of miles traveled /gas purchased(or added to tank). THIS IS NOT FUEL MILAGE BECAUSE WE ARE ASSUMING THAT THIS FILL-UP QUANITY IS WHAT WE CONSUMED! 99% of the time it is not, it is just what we put in.
These filling errors can be minimized by continuing the test over as many fill-ups as possible. It is these errors that enables the fellow next door with the '62 462 inch Lincoln to get 20 + mpg. He knows he went 120 miles and he knows he PUT IN 6 gallons. But the car was sitting tilted with the filler neck down low, impossible to fill properly-probably could not put too much in tank- if level perhaps another two gallon would fit in thus giving him 15MPG-hmmm not much to brag about-but boy 20 SURE IS.
Tom's old '65 has a simple tank compared to a '72 vehicle which has an evaporative emmissions tank, they have odd bumps to their shape to satisfy their need for areas of vapor for cannisters to collect from etc. You can click off gas pumps for days and not fill them up. His will make it a bit easier to fill-up uniformly/accurately.
In order to make this test an accurate venture, a good round trip total should be considered without breaking it into several low milage jaunts.
Sorry to be seemingly pouring rain on the parade, as I am as interested as anyone in seeing if a 250 can deal with 2.56 gears. Any one can short fill a tank and get bragging rights quite easily for only one short distance fill-up-but boy check the milage on that next tank... 13 ??... what happen to the 22?
