What's the mpg's capabilities of these trucks? I realize it will vary depending on many factors so i'll try to be specific. My truck is a '75 F100 2WD with the inline 300-6 engine and NP435 4-spd. trans, and 3.23 gearing w/31" tires.

The engine is basically stock with the exception of an aftermarket carb/intake and header. On the highway over the course of 1K miles, driving a steady 70mph I'm averaging 21mpg. Is this pretty much par for the course?

 

I'd say 21 MPG is outstanding even unusual. You have about the best "theoretical" combo for mileage (1/2 ton, 2 wd, manual transmission, 300 I6, moderate rear ratio). With 4 WD and V8, high single digits are the norm. Your tuning is probably well sorted out.

 

I had a bud with same setup you have basically and he usually could get around 18 highway. Slow speed wasn't really that great but highway it was so nice drive. I loved how soft it rode at how little gas it seemed to use.

 

I was pleasantly surprised myself. The previous owner told me to expect 20-21mpg on the hwy. but I assumed he was just giving me his best sells pitch. After two months of driving I now know he was correct.

If I go above 70mph the mileage does drop off, to about 18mpg, same goes for driving around town, about 18mpg, which is to be expected. 65-70mph seems to be the "sweet spot" for best mileage when cruising the interstate.

 

That is exceptional mileage for these trucks. I could push 20 MPG in my '79 with a 300 and C4. It had 2.72 gears and 235/75/15 tires

 

Only way I could get that outa mine is if it were on a roll back wrecker. That is outstanding mileage and you have the best set up for it it seems like.

It might not win the race, but is will sure let you drive by a few gas stations. And these days that the best deal going.

 

390, C6, 9" 3.50:1, Holley 350 61 jets, MSD Blaster 2, breaker points, synthetic oil with additiv, 20" vacuum at idle,*
Mr Gasket 925D, thermal fan clutch, dual exhaust, 38 psi in P-metric tyres, 235/75-R15, 18.8 mpg below 55mph.

 

anything north of 15mpg is pretty good IMO.

 

I get 12-14 MPG on my 2 barrel 360ci with a C6 and 3.25 rear end if I use a light foot on accelerator pedal.

 

78' F250. 400ci, C6 tranny. 10mpg no matter what I do. Tow a Sherman tank uphill or cruise on the freeway empty at 60mph.

 

1975 F100 4x4 SB 360 NP435 4.56 gears with 33 tires, spinning 3k rpm at 65mph I get 13mpg

 

I miraculously got almost 13 mpg out of my '73 4x4, 360, 4sp, 33s and 4.10s.

 

all the emission equipment is off my truck with the exception of the PCV. From Prescott AZ to Tucson I get 13 mpg, going from Tucson to Prescott I get 12.5.

I am working on swapping in some sort of Overdrive, thinking a Auto swap to a E4oD to reduce the RPM at highway speed.

 

74 F100 390 two barrel Motorcraft, stock except for dual exhaust, c6 auto 3.50 rear gears, 235/75r15 tires, around 2750 rpms at 65 mph. So far getting between 12 and 14 mpg highway.

Thinking about swapping to 2.75 rear gear... but will it help the mileage? I would like to get over 15 mpg and be able to drive 70 mpg without winding it out so much...

 

My 460 in my f250 gets 10-11 mpg. Holley 750 cfm carburetor. 3:11 gears. 16.5 x 8.75 tires.