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I currently have a 1978 f250, with a 1997 460 engine that has a 4 barrel carb. It is a fun truck to drive and gets decent power, but I would like to increase the mpg to above what it currently is, which is around 6-8mpg I’ve estimated. The engine is entirely stock minus the 4 barrel.
Welcome to FTE! Bottom line, the best a 460 will get IME is 12-14 and that's driving it with an egg under your foot, on the hwy doing ~57-60 (depends on gearing and tire size) mine was 4.10's and 35's on a 94 F350/4x/CC but the rest of the time it avg. 10, empty or towing, didn't care.
You have a gas sucking beast pushing a brick, best way to get better mpg's out of your 78 is to throw a 300/I6 in it with an NP435 4.10's w/33's
Originally Posted by ckemppai
Hi everyone
I currently have a 1978 f250, with a 1997 460 engine that has a 4 barrel carb. It is a fun truck to drive and gets decent power, but I would like to increase the mpg to above what it currently is, which is around 6-8mpg I’ve estimated. The engine is entirely stock minus the 4 barrel.
More MPG? Get a new truck with a V6. Even those will only get about 20 on the highway at best. $50,000 will buy a lot of fuel.
As alluded to above, if you want fuel economy these trucks aren’t for you. Even if you put a smaller engine in it or something more modern like a Coyote, physics is not your friend. Lots of mass, a terrible drag coefficient, and lots of rolling resistance will result in you never seeing a return on your investment.
Just wait out the higher fuel prices. They’ll come back down again like they always do. In the
meantime, put a vacuum gauge and timing light on there and make sure your carb tune/timing is adjusted for maximum vacuum at idle. It’s a amazing how much more fuel a carb will
suck down when it is even slightly out of tune.
Last edited by Viper Pilot; May 4, 2026 at 07:43 PM.
A really good place to work to get better part throttle economy is the calibration of the idle feed in the carburetor. The idle feed restriction feeds not only fuel to the idle screw but also to the transition slot and the slot is what feeds about 90% of the fuel that the engine uses. Most of the time they are way richer than needed. A good test is to take a stranded electrical wire, strip off about an inch and use one strand inserted into each idle feed restriction in the metering block(assuming a Holley carburetor). This will trim the mixture in this circuit leaner by about 10% or so. Readjust the idle mixture screws which should be out from seated about 1-1/2 turns if the mixture being fed to it is about right.
Overdrive ($$), EFI ($), re-gear ($-$$), stock height or lower it ($-$$), more efficient engine ($$$).
Ive been chipping away at little things that sorta make a brick slightly more efficient. Aero can be big, and air temp (density) contributes as well.
An air dam can help, smoothing the front end out with some clear acrylic over the grill and headlights (leave an opening for radiator).
460s & 429s are not known for efficiency. One of the fellas on here mentioned he has one that’s running Propane at half the cost of gas. That would give you the best bang for your buck.
Otherwise:
This is only for winter, and it helps a lot with the truck warming up better, letting the T-stat do the temp regulation, instead of all the 40* air through the grill.
I managed to get 13.5mpg at 50*, a little in town driving, a jaunt up I-5 and back, doing 75 at times. 1:1 final, 3.54 gears, 32.5” tires, and an FE.
I’m going to wait til summer when I can lean out the carb, and try another run on flat interstate and shoot for 15mpg.
I spent way too much getting here; I should’ve just kept the 429 and C6 in there.
He has an older Toyota 4x4 and a mid gen Prius. While some of the write ups get way too technical for some, you can glean a lot of good info.
One of the other mods I’m planning will start with using plastic sheet to cover the gaps between the bottom of the body panels and the frame. Also blending fender flares into the air dam. I’m just using HDPE sheet from Speedway Motors. It comes in rolls and is affordable and semi-rigid.
At some point I may also make a skid plate, but the truck is so long it seems silly.
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