1981 F-150, 302/C6.

I have a very unique (read: work in progress) combination of engine parts right now on my truck, and while I know it's not particularly the most optimal setup, I'm trying to get the best mileage out of it as I can until I can afford the right parts. Right now my engine has

- Edelbrock 1406 4bbl carburetor, rebuilt about a year and a half ago
- Factory 2bbl intake with adapter plate to allow carb to fit
- Distributor recurve kit installed in factory DSII distributor
- MSD 6A multispark ignition box with Blaster 2 50kV coil
- OE Autolite (or Motorcraft, can't remember) plugs, .060" gap
- Factory exhaust with factory style muffler, single 2"

The truck runs very good and is perfectly reliable, but compared to the Jeeps I'm used to driving, it's hitting the pocketbook pretty hard. I know a new intake and exhaust would help it alot, but that's out of my financial reach right now. I'm spending quite a bit already on new tires and ball joints as it is.

BTW, for those who might wonder, the reason I ended up back in the truck was because my green Cherokee met its demise in Dallas after getting t-boned by a cop car at an intersection, and the white Cherokee started having major top end clatter and knock so I parked it (at 239,500 miles).

 

The only improvement you could make would be the transmission. The c6 is a little bit of a gas hog. If you could get a overdrive tranny, it would help but in your case probably only a mpg or 2, since you already have a 2.75 rearend.

What are you getting by the way? If you are getting 15 or 16mpg, I don't think you could hope for much more.

 

I'm probably getting about 9-10 at best right now. I plugged a few vacuum leaks and that seemed to help both the mileage and the overall performance of the engine.

I don't know if changing jets in the carburetor would help anything. It's already pretty conservatively tuned being as it's the 1406.

 

Make sure your tires are fully inflated.

Beyond that the factory Y pipe is a restriction. The CatCo pipe is pretty good or you can roll your own. I'd do that before a trans.

You can work on the carb jetting and lean it out.

 

I would close that spark plug gap up to .045". What size tires are you running and at what psi?

 

The C6 is really a gas hog, as Dave said. But you should be getting around 12 - 13 MPG with that setup, if not more. I'm getting that much with Rusty. However, how you drive it is important. These trucks have horrible aerodynamics, and trying to drive them 70 MPH is going to really hurt the MPG - but still not that much.

On the carb, the 1406 is jetting slightly lean out of the box, so it's jetting isn't what is killing your MPG. You may be able to lean it a bit more, as I've done, but it won't get you much improvement in MPG. However, if the choke isn't coming off it will kill MPG. Check that for sure.

Beyond that, check to see if your brakes are dragging. I've had fits with the fronts on Dad's truck, although Rusty seems fine. Ditto the rear brakes. And check for vacuum leaks.

 

NTEA | Reducing Fuel Costs the Old Fashioned Way (Part 2)

 

That's a good read. But, it says aero drag goes up by the cube, not square. I didn't realize that. In fact, I'm pretty sure in my physics classes it was squared - although those classes were about 50 years ago, so.....

 

I remember it as, there is "a lot" more drag at 70 MPH vs. 55 MPH... all that physics stuff is for physicians.

 

They say that's why they went to the aero plastic headlights in 87, getting rid of the headlight buckets in these trucks. A little bit here, a little bit there I guess.

 

Yes. The 80 - 86 trucks may be the all-time worst on aero. With everything recessed, such as the headlights and grille, they grab onto the wind rather than allow it to slip past. Worse than the proverbial barn door since it doesn't have any recesses.

So, to see what was needed all you have to do is compare an 86 to an 87, which has rounded and smoothed everything. That surely made quite a difference. Then they added a much larger chin spoiler, which I think was on all 87's vs the itsy bitsy one that was on a very few 86's, to reduce the amount of air going under the truck. And, as you say, a little bit here and a little bit there.

 

TheKirbyMan,

I drive with the desire to do the best I can regarding gas mileage and have some ideas which help with whatever engine/transmission combination you find in your truck. Some have already been mentioned in prior posts.

1. Make sure the engine is in its best state of tune.
2. Make sure the choke operates correctly.
3. Make sure the brakes do not drag.
4. Make sure the alignment is correct.
5. Eliminate weight when possible.
6. Roof mounted lights, racks, etc. create drag.
7. Use the highest temperature thermostat possible [195F].
8. Run the highest recommended air pressure in tires.
9. "Street" tires will likely give better gas mileage than aggressive "off-road" tires.
10. Oversized tires are heavier and require more energy to get rolling [and to stop].
11. Make certain the speedometer / odometer are correct [especially if tire sizes or axle ratios have been changed].
12. Allow the C6 transmission to shift into high gear as quickly as possible. [The discussion about changing to an O.D. transmission is correct, but does not address the fact that you will have to drive thousands of miles @ +2 mpg to pay off the expense.]
13. When you drive, pretend that there is an egg between your foot and the gas pedal.
14. Probably should be included in #1, but have a clean air filter element.
15. Have the hoses connected to the air filter snorkel which supply warm air @ start-up and cold air once at operating conditions.
16. Use the thinnest oil possible [synthetic?].
17. Some have good results with the use of synthetic transmission fluid and differential grease.
18. Cruise at speeds of 55-62 mph.
19. This suggestion likely will bring out differing opinions, but use the lowest octane gasoline possible without excessive pinging or knocking.

Hope this list will help! It has worked for me.

 

Well done, David! Reps to you.

 

Thank you, Mr. Lewis!