Here's the hypothetical: 4x4 F150, 1996 and earlier, mostly lightly loaded, highway, stock tire size.

What would be the best configuration to maximize MPG (vintage, motor, transmission, gears)?

Roy

 

4bt cummins swap would be pretty good.

 

How much weight is lightly loaded?

 

Oops...I forgot to add, "gas, OEM," to the specs.



Lightly loaded:

80% one person, nothing in the bed;
20% 2-people, 300# in the bed, 2 canoes on roof racks.

No trailer, ever.

 

You said highway so I would go 300 i6 5 speed 3.08. Some hypermilers claim to get 20+ with this setup, but 17-18 would be more realistic. A lot of people say the older carbed 300 with a 4 speed and 2.7? Gear get better than the efi. Idk, never had one. Terrain in your area will play a big role, if you live in the mountains like me, a 3.55 might be a better option. I get 16.5 driving nice with a 300 auto reg cab lwb 2wd 3.73. I travel mostly 55mph hwy. never had it on the interstate with this gear. Last tank was only 13 when I drove the truck back and forth to work with a bunch of red lights. In contrast, a 5.0 will make a much more enjoyable interstate ride, my father-n-law has a 90 302 4x4 swb 5 speed that gets about 12 around town. I don't know what his gearing is but its factory so 3.08 or 3.55.

 

I had a full-size Cherokee with the 258, carb, 3-speed manual, and something like 2.75 gears and it got ~ 20 mpg. Makes me think a F150 with a 300 and ~2.75 gears would be a good match.

I am a fan of in-line motors, but not a fan of internal slaves (which I think all the F150 5-speeds had).

I understand you can't have everything you want.

Roy

 

I have an 86 F150 4X4 reg cab SWB 5.0 EFI with SROD and 3.55 gears that will easily do mid 20's with 235/75/15 highway tires. I previously had a 92 Bronco with 4.9, E4OD and 3.55 gears that managed about 15 mpg. Truck had 30X9.50X15 Goodyear Wranglers. Not enough difference in displacement between the 5.0 and the 4.9 to make much of a difference in fuel consumption. Suspect the difference here is in curb weight, tires and transmission.

FWIW, I used to have a 73 Bronco with a carbed 302. It got around 20 mpg. When the 302 blew up, I built a mild 351W with a 4bbl. Hooked it to the same 3 spd manual and got about 1 mpg better. Was also able to light up all 4 tires, but that's another story.

A lot of the mileage results will also vary with pressure from the right foot.

 

Wow.

That SROD was a 3-speed-plus-OD manual, right? Aluminum housing? External slave?

Your 302 to 351 story is also interesting. OD, gearing, tires, the right foot...makes a lot of difference as opposed to CID.

Roy

 

My 95 150, 5.0 m5od 3.55s 4x4 with 31x10.5 tires will hit between 15-19 dependent on how I drive frustrated with traffic 15 most of the time its 16.5. When I got it with 155k on it after I tuned it up she would do 20 on long trips but at more than 240k she's getting tired and don't road trip her anymore.

 

Um, mid 20's.... How do you figure fuel mileage? Are you Canadian? New 2wd ecoboost don't get that.

 

5.8L/E4OD/3.55 with 235/75R15 tires will net decent, though not best, mileage. I frequently saw 17mpg highway at 65mph (empty). Add a headwind, excessive rest stops, more speed, etc. and that number goes down pretty fast. Had a few fluke tanks, both higher than I thought possible and lower than I thought possible: 20.5mpg (tailwind on glare ice for 300 miles, no stops, 45-50mph) down to 7mpg (towing at trucks rated limit). Realistic average highway was 15, that's what I used when figuring trip costs and it worked out well. Added tall tires, small lift, flatbed, and mileage peaks at about 15mpg now, with a realistic average closer to 12 or 13. In town, don't bother calculating it...

 

Hands down 1996 5.0 5 speed 3.55 gears
Hard to beat 205hp/275ft/lbs/tq
With the auto you lost 10hp

 

For comparison, the 1996 4.9 was:

150 hp @ 3400 and 260 ft lb @ 2k

 

I have heard (but not done) 27 MPG in a 80-83 2wd F100 with a 300, manual, and 2.73 gears, with a slight downhill grade. I believe I saw this claim in a 80s Ford advertisement

EDIT: This claims 29 highway

 

with a "slight downhill grade" all mileage claims are hopelessly skewed.
as for 27mpg in a full-size pickup ... extraordinary claims require extraordinary proof (heck, i would even settle for ORDINARY proof).