I WANNA BUY A 1985 F350 6.9L 4 SPEED, 3.55 GEARS, OR 3.73. WHAT KINDA HIGHWAY MPG DO YOU GUYS THINK I'LL GET? I DO PLAN ON GETTING A BETTER AIR INTAKE, AND A HIGH PERFORMANCE EXHAUST.

 

Its not going to break any records... I would guess in the mid teens at best.

Not much to do about exhaust, is it a turbo or NA?

 

NA.

 

Performance air filter isn't going to help much, and they let too much dirt and dust into the engine anyway. You might get 20, but that's if you drive it easy.

 

with mine, 4 speed man, 3.55 gears and 35 inch tires. i got 25mpg on the highway.
75 mph from lima ohio to quakertown pa, 600+ miles on 2 tanks of fuel. 16 gallon tank.
15 around town. truck loved to cruise.

 

16-17 max hwy

 

hey diesel crawler how come the old diesels got rly good milage hauling *** down the highway? i used to have a gm 6.2 and it got like 22-23 when i held it on the floor bored going down the interstate... like the camo paint job

 

was never quite sure, unless the air flow into the intake at higher speeds aced like a little turbo? but never figured out why it got so good.

mine wasnt to the floorboards. the truck would do 105 before it hit the engine gov. so at 75-80 i was probly around 2500-2700 rpms.

 

mabey the injector pump leans out or somthing, my 12 valve the faster i drive it the more fuel it sucks

 

You GAS MILEAGE will be excellent! Your truck is a diesel!