horrible fuel mileage

[goodyg92]

i am getting horrible mileage i have a 7.3l idi turbo and i am getting on average 6mpg i have 38.5 in tires what kind of gears would be good idk what is in it but floored on the highway i mak out about 75-80 top speed any suggestions on what i could do to get better fuel economy if it is even the gearing? anything other than gears that anyone can think of?

[SIC-E]

first off, if using odometer to calc mileage you are way off given 38.5" tires. def need to change gears with that tall of a tire.

[goodyg92]

yeah i am looking for a set of 4.10 or 4.30 used but they are hella hard to find but i dont have the money to get a respeed calibrator

[cdnsarguy]

Would you post some info re your truck in a signature...... is it auto or manual trans.

Check the door post label for the axle ratio.........

Axle codes

Ford Axle Code Chart .: Articles

Automotive What is my Ford rear end ratio, do I have positraction

[boracay]

tall tires give you higher gearing ,thats why to keep the same power and gear ratio its necessary to change the gear set. taller tires to lower gears you can also jack up your truck -draw a line on the bottom of the tire to the floor - and mark the driveshaft against the diff . then rotate the tire one complete turn while counting how many times the drive shaft rotates , for example 3 3/4 would be 3.73 gears i have 33 's on my truck and ihave to add 8-9 miles per hundred on the trip od for the correct millage [ checked against two diff gps 's ]

[M.L.S.C.]

To the original poster - yes, if you have 3.55s with that large tires you do need to regear. Our engines make most torque in the 1600-1800 rpm band, while being most efficient about 200-300 rpm lower than that, so if you're in the 1300-1400 rpm range when you actually demand high torque output you'll be loading the engine a bit too much and you'll be burning fuel like no tomorrow.