1980 F-150 4X4 4.9l with carter YF carb.

235/75R-15 tires NP 4 speed manual trans and NP 208 transfer case, gears are 3.54.

If not loaded 22-24 MPG, if really light footed 26 MPG on long haul flat ground. In town any where between 16-20 MPG. New stock engine has less than 500 miles.
And passes CA smog.

irhunter does your state require smog emissions testing? This would change a lot of options.

 

GMC,

No smog testing. Maine used to have it down south where the people live; here, up in the woods, there has never been testing. Maybe it was when ethanol hit the gas, they stopped testing even down south.

Your MPG numbers are great. Were taller gears available as original with the 4WD? I was looking at a '95 2WD with the E4OD and 3.08 gears.

 

expect low 20s to high teens with that combo, with a 92 and all the other stuff i get low 20s

 

I'm reminded of how cool it is/was combining dual fuel tanks with 22 mpg economy.....total range between fillups of 836 miles!

 

i read on a different thread something about the 84's and an economy package that had tall gears and maybe something different with the crankshaft, or timing i think it was timed different and had a low hp output. which would move your power-band into a different operating range; depending upon you application could achieve greater gas mileage. i know the efi are timed 2 degrees different from carbed models.

the engine itself is only going to get you so much mph your mileage will be in the drive-train, we are talking about 60's technology gas was cheap and plentiful.

sorry i am ramblin a bit i am a new father and a little sleep deprived

 

I used to own what is now my son's 1984 F150 with 4.9L, 4 speed manual O.D. and 2.47 rear gears. It would return 26+ mpg [before the advent of gasohol] on the interstate @ ~60 mph.

I have read from one source that the trucks equipped with 2.47 and 2.70 rear gears were equipped with a different camshaft, BUT most sources disagree and say that all camshafts for 300/4.9L engines were the same specifications.

 

How ever they got 26 mpg in a F150, one has to ask "what happened?" I mean, today engines are so much more sophisticated and can't come close to that mileage.

I assume it is a combination of factors. Heavier, taller-looking-body-style, better acceleration, cleaner. But, it still stinks.

And, it is not just full size trucks. I had a '78 Datsun truck which always got >30 mpg.

 

Factors...overdrive, differential, higher-pressure tires, a basically economical engine especially for a 300 cu in, a driver who brings the shift points to a lower rpm.

 

...and drives like an old man with an imagined egg between his foot and the accelerator.

 

My 82 F-100 has a carb'd 300, 3 speed, and a ridiculous 2.47 rear end gear. On a trip of 100 miles of straight, fairly flat highway driving, I was getting 27mpg. This was, as I found out a few days later, on 5 cylinders.

Tweaking the timing and carb a little (and after a full tune-up), I was able to touch 30mpg on the PA turnpike, although I was a few MPH below the limit and was getting passed constantly. I didn't mind, I was enjoying doing so well on gas.

Oh, and as for city mpg - even if I baby it and shift early, I MIGHT do 15, tops. If I'm in a hurry, 11-12 is more like it. This thing does not climb hills or enjoy heavy throttle at low speeds.

 

The very impressive highway mileage is due to the 2.47 rear gears and your driving style ["although I was a few MPH below the limit and was getting passed constantly. I didn't mind, I was enjoying doing so well on gas"].

The more normal city mpg is an example of the fact that your F100 is still a heavy weight in which power must be used to get it in motion.

Thanks for sharing your observations!

 

My truck, 95 F150 SC 4x2 300 5 speed 3.08 gears and 31" BFG AT tires will get 20 Mpg at 60 Mph. If I go 70 -75 the mpg drops down to 18. I get about 16.1 to 17.5 Mpg on average back and forth to work.
Although I have had some Chevy trucks that got better mileage with the 4.3 and 5.0 they were not as versatile or dependable as the 4.9.
Regards
rikard

 

1985 4x4 300 with 31- 10-50 tires best i can see is 16 --that s feather footing it TR

 

If your truck is carbed and getting poor mileage, a couple of places to look are (1) a timing problem - not enough centrifugal and/or vacuum or initial or (2) the jet(s) in the carb. Some carb rebuilders will put whatever jets they have in stock into the carbs - just so they can get them out the door. They may or may not be the correct for your application. As most of you know, these are very basic ideas, but they might just help someone....jack

 

Back in 1984 , my new sticker stated 17 highway ,13 cityTR