75 F100 4x4 w/ an unconfirmed 390 4 barrel Edelbrock and a C6. My odometer is, well lets call it suspect so based on my GPS speedometer/odometer I'm at 8.5 - 9.

NP 203 with manual hubs but I don't know if it has an actual part-time installed or not, surely that doesn't help. Getting some blow-by in one of the cylinders, haven't checked compression but based on the overall condition of the truck I would speculate that it's old, tired and well out of tune.

 

In addition to the aerodynamics, I'd guess the tires instill a lot of roll resistance. For example, when I go into town, the speed limit drops from 55 to 40 to 25 pretty quickly, but I don't need the brakes to slow down

 

74 F-100 390 C-6 auto, 84k original miles, stock 15 inch tires and 3.50 rearend gears.

Overall average is 11.6 mpg so far, with a best of 17 mpg driving 55 mph all highway miles. The lowest so far was 8.7 mpg - once pulling a load at 70 mph and once just having too much fun.

http://www.fuelly.com/car/ford/f-100...mgussey/399189

FWIW, my average with the 01 Ram v-10 5-speed is 12.2 mpg so far...

 

Hi all,

been awhile since I've been on here and was just getting back on here to see about if anyone here locally or near by me, in Olympia, WA area knows of a good mechanic that can help me get my carb tuned up and running better so that I can try and get my MPG up a bit. I tested it one time and it was pretty good if I kept my speed at about 55, and now it's lower even though I'm still driving it at about 55-58, if I go over 60 it really drops off a lot. Anyways, any help would be appreciated on helping me find someone who can help me get my MPG back up a bit. Thanks.

 

Best investment you will make will be an o2 sensor in your exhaust with a gauge in the cabin - check out 'Innovate o2 gauge' on ebay and you'll get some nice results under $200 for the full setup. It will help you tune your carburettor to just what you need by giving you accurate real time feedback - think of it as a rolling road or dyno in your dash.

But, back to the thread... the 351C in my Landcruiser with 35" tyres, 4.11 diffs and 5spd manual trans got a solid 12mpg highway.

My father's stroked 408 Cleveland in his trayback '79 F350 gets about 12mpg average, but cruises at 15mpg highway. He is running the NP 4spd manual trans with a GearVendors unit at the back, and standard 16x7.5 tyres.

Rolling resistance is huge with these old trucks. Higher tyre pressures and stockish 16x7.5 tyres with highway-oriented patterns will help a lot, as will new wheel bearings, U-joints, and diff/trans case/gearbox fluids. Trading big side mirrors for smaller car-style ones, removing external sun-visors, and cutting weight where possible will help a bit with the rest. If you want to get serious then a tapered 'kammback' type canopy will also help with freeway mileage, as well as a manual transmission and gears that see you pulling between 2000 and 2400rpm in your freeway cruise speed.

/rant over