hey all,

If I wanted to do a build focusing on cruising and mpg more than power or towing ability, what would be a good setup for a 78 f100. Its automatic atm, but open to changes. and I don't really know much about gears in the rear so feel free to educate me. Feel free to recoment anything from a different block to EFI. Im game for any ideas. Just kinda thinking about it. Like I said, I want something that cruises. That doesn't scream at highway speeds

 

It's really hard to gain mpg in our low-aero and heavy trucks. Which engine do you have? I know the 4-wheel drives only had the 351m or the 400, but if yours is 2-wheel drive (sounds like it, as a 100, correct?) then you could have had a 302 or even a six-cylinder. Correct?

You may have to test to see what gears are in the diff, unless you've owned the truck since new and the axle tag is still in place.
Otherwise you'll need to do a few steps to determine the gear ratio in there now. And yes, gears can make all the difference.
Well, all the difference in power and pep, if not exactly making big changes in fuel economy.

But, some things to consider that are universal, if not always making a huge difference.

1. Better breathing exhaust. Doesn't mean 4" duals with glasspacks. Just something quiet but with breathability.
2. Synthetic oils. Not a huge diff, but can still take away some friction. Also makes a good excuse to change the gear lube in the diff.
3. Tires! Tires can make a huge difference. Not just size, but load range and tread/carcass design. On cars it's more noticeable than on trucks in my experience, but it's still there.
4. Weight. Put the truck on a diet if you can. I carry tons of crap in the form of spare parts and tools and urban survival gear. So light weight is not gonna happen for me. But it does help as well.
5. Better ignition timing curve perhaps? Updated ignition components in other ways can make it run better and feel more powerful. But because of the aero really don't result in mpg gains very often I don't think. But they're still helpful.
6. Carburetion. Just not sure which way is better as I've only experimented with the stock 2bbl on my 400. On my 302 however I've used four different carbs and the only one that got me a mileage increase took away all of my ill-gotten gains from all the other things! So it only lasted a short time even though I loved the immediate accel off of idle, and the extra 2mpg I got from it.
7. Aerodynamics. Can't argue with success. But I don't really know any tricks to getting better aero on our bricks-in-the-wind trucks. An effective air dam below the front bumper is a good start. But only if you don't use this thing as much of a truck other than on the street.
8. Almost forgot... Speed! With our trucks, to get better economy, you need to play the patience card. Keep it slow, as in 55-60mph, and it can do wonders.

Now, with all that said, the best mpg I ever got was with the truck literally loaded to the gills and 400 lbs above it's rated maximum GVWR of 8550 lbs. Helping a friend move from here in San Jose to Sequim, WA I got almost 14mpg on the way up. With more uphill than down sometimes!
But on the way back, fully empty and a lot of coasting downhill, it went back to the just over 11 that it normally got. Go figure.

I've had three vehicles now, that got better mileage with the throttle mashed further into the floor with the same vehicle speed. Must be something about volumetric efficiency or something. Dunno, but it worked.
Still have the damn scratch in my paint too, from the kid pumping gas because I couldn't do it myself!
But that's fodder for another whine.... uh, I mean story.

Good luck.

Paul

 

2wd?
put truck body on '04-up crown vic chassis. 4.6/auto. I bet you could pull high teens mpg and would cruise very nice.