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How to improve MPG in an old truck

nyc123

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Hi, new member here. I had an 82 F100 but sold it because I was making Saudi kings and Texas tycoons rich. Is there a way I can get 20+ mpg, maybe even 30, out of an old 70's or 80's model truck? My options I was thinking was doing a modern swap for a new engine, wiring, etc., and the other option I was thinking about was if there's something I can do to greatly improve the MPG on an old truck from those years. I think I was getting less than 10 MPG in that F100. Any suggestions on an old 150/1500 size truck with certain specs that would make this more doable, please let me know. I am just looking at what to buy now, but I like pretty much all the late 70's, 80's, and even up to mid 90's trucks. Ford, Dodge, Chevy, GMC - I'm open. I have to say, I really like how the Fords look (I know that's probably gonna tick some people off but I'm not a truck expert at all). I would also like to keep the good sound of an old truck (I had a friend suggesting making it electric...). I think if I could it with keeping the old engine, it'd be best, since I'm assuming the resale value is a lot of the old engines. If I could get an idea of costs, too, I'd appreciate it. If it costs way more to do the modern engine rather than modifying the old ones, that would change the outlook
 

7mopar

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Guess it would be possible if you are willing to throw enough money at it. 30 MPG would be a stretch unless you are will to do a diesel swap with overdrive.
 

65 sporty

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Modern drivetrain would be great, but not 30, maybe mid 20's. Like 7mopar said, diesel swap and overdrive and you still would be stretching it to get 30.
 

7mopar

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I have heard of one Ram 3500 diesel that got 32 mpg unloaded. Manual trans with od plus a gear vendor. It possible but at what expense.
 

nyc123

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How much would a diesel swap with overdrive probably cost? Couldn't I just buy an old diesel truck? Overdrive you mean gearing?
 

66fs

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Some of the 70's and early 80's Ford vans with the 300 and manual O/D used to get around 30mpg on the highway.
 

7mopar

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How much would a diesel swap with overdrive probably cost? Couldn't I just buy an old diesel truck? Overdrive you mean gearing?
You could buy a running truck with overdrive and add the additional unit for less than the cost of a swap and have a nicer truck.
Dont know what the cost would be. Around here $10000 doesnt buy much and what you a suggesting could go well over $20000.
 

Cranky1

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My 97 Cummins powered Dodge 2500 has knocked down 25 mpg at times and does high teens pulling a an open trailer with a 71 Duster on it. Weight of the trailer with the car was around 4400 lbs and running 70 mph with it. If you like to do a project, a 4bt Cummins can knock down 30 in a smaller pickup like a Dakota but you got to do some fab work to get it in. The 2nd gen Dakota (97-2004) tips the scales in the high 3000 lbs range and higher depending on configuration and options but you can bump up the tune on the 4 and have pretty good performance and mileage. Why Dodge never did this at the factory is beyond me.....
 
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nyc123

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wow, 10 and 20k

Is there a way to at least get 20 in an old truck? Maybe some sorts of doohickeys put on the engine, or fabrication here or there? What about dropping an old LS motor in it? <----I heard that somewhere else

I have a couple buddies who are real good at this kind of stuff. Necks are as red as it gets and they've done this for years, but not for mpg
 

7mopar

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Dodge doesn't offer the diesel in the new Dakotas like they do in the 1500 Ram? I gave up on looking at new trucks long ago. Just to expensive.
 

Cranky1

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Dodge doesn't offer the diesel in the new Dakotas like they do in the 1500 Ram? I gave up on looking at new trucks long ago. Just to expensive.
Seems the Dakotas didn't get a lot of love from Dodge. How many commercials did you see since they were first produced? And if Dodge did offer a diesel in one, I've never knew about it either.
 

volaredon

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my 79 D100 with slant 6 and 3 on the tree would get 22 on the highway. No overdrive, 3.55 rear, when I went to a 318 with 833OD, small cam, (I chickened out and went even smaller than my 1st choice which was a COMP 252) I didn't know much at the time, this cam was between the stocker and the 252, was a MP "purple shaft". '69 318, with the smaller chamber (stock for 69) heads, Eddy Streetmaster 318 with a Carter Competition series AFB, # 9626 as I remember, wound up going to a 3.91 after I killed the 8-1/4 that was stock/ I put a 8-3/4 in out of a '69 and the 3.91 was what it came with
Manual steering and brakes, shortbed. I got the same economy from that combo as I did from the original combo.
WHEN I drove it sanely....
I also had an 81 W150- stock with 318 and Carter TQ, 3.21 gears, 32" tires, 727 that also got the same on the highway… unusual but true. None of the trucks I have had since could touch these in that department... I did have an 87 B250 van (another 318) that came close.
then on the other end, there was my 88 D100, 1st year TBI 318, that was good for 9 MPG downhill... I spent a lot of "good after bad" money trying to improve on it..... finally wound up selling for a huge loss....
I have been in a "Dakota rut" for the last 10-15 years.... best of them was (again) 22 MPG, a 93 318 club cab that I converted to a stick. I still miss that one. and the '81.
 

AJ.

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Those old trucks are huge and heavy bricks and they take power to push thru the air, and the faster you go, the worse it gets. So if you really want one of those, you are gonna have to figure out how to make it take less power to push it thru the air.
Here is some help; the rule of thumb is that it takes about a half a pound of gasoline to make one horsepower continuously for one hour.
Lets say that old truck might take 50 hp to maintain 60 mph. Therefor in 60 miles it will consume
50 x .5= 25 pounds of gas. At 6 pounds per gallon, that is
25/6= 4.17 gallons. The end result then is
4.17 gallons to 60 miles, or 14.4 mpg

But if you can aero that truck down, or lighten it up, to say a 40 hp requirement, then
60 miles /(40x.5)/6= 18 mpg.

But a better idea is to just start with a smaller lighter more aero truck at say 35hp requirement; then
60/(35x .5)/6=20.6 mpg
So now; you can begin to aero/lighten this truck to say a 30hp requirement or
60/(30 x .5)/6=24 mpg.

And finally;
Now you can start to "cheat " the above rule of thumb by;
Leaning out the cruise circuit, or
increasing the engines efficiency, or
reducing the number of cylinders, or
the number of cubic inches, or
the method of power transmission, or
by bringing down the rpm, or
installing EFI, or, or, or.....
So long as the engine can still physically cruise at 60 mph.

With a carb, a low-compression V8, and a 3speed auto trans, it's gonna be doggone hard to break into the 20s.

To help you get started, I suggest;
a 2-wheel drive,fuel-injected regular cab short-box, light-weight, first gen Dakota,with a 5-speed manual, or an A500 trans,and a hiway rpm of sub-2000. Then lighten it, lower it, modify the running gear so it rolls easy, and install tall, skinny, hard tires; at a million psi.
The engine can be just about anything if you are just looking for point to point economy because the hp requirement to cruise is the same, leaving just engine friction as the major difference, and, I guess, in that game,6 cylinders outta trump 8.
Of course any engine you use, will have to be in tip-top condition.
And the bigger the engine, the more fuel it will use when not cruising.
My money would be on the 5.2 Magnum.

Not all carburated engines are able to cruise well at sub 2000 rpm and it is impossible to give that engine the proper ignition timing, at sub-2000cruise rpm, with a factory distributor-type ignition system. So, you will have to spring for a programmable timing computer.

And just for kicks; you know how much headroom is in that cab? I'll guess 6 inches could be cut out with bucket seats, and that would reduce your frontal area by about 2.75 square feet! which maths out close to 10%. That is huge. Not sure what it would look like tho...............

BTW; the aftermarket makes fiberglass fenders and bedside panels for the 88 to 96 boxy models. It ain't much, but it's something,lol.
 

volaredon

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nope.. I have had both 6 and 8 cylinder Dakotas, in my experience the 8s have never gotten "worse" MPG than the 6 cyl equipped ones. in fact my "mileage champ" of the bunch was a 93 club cab with a 318 Magnum that I converted to a stick.... sadly wrecked way beyond repair. I wanted the 5 speed setup off of it back, but I was so pissed at the fact it was wrecked I just said "screw it".... and sent it off to the junkyard.... a $300 ticket+ a mandatory missed day from work for court, for that ticket plus barely being able to move for a couple weeks, plus having to go buy another truck so I could get to work, (that the insurance co raked me over the coals for the next 3 years on) added up to lots of frustration at the time. lots of money spent that did not benefit me or my family one iota. nor did it benefit the "other guy" one bit either..... nevermind.
Replaced that truck with a 92 318 club cab, that was "close but not quite" the truck that 93 had become....
sorry for the rant, but I really liked that truck.... I now have a 96 4wd with a 318 and a 99 club cab with a 3.9 that is a "dog" and only out does the 4x4 V8, by 2-to 2-1/2 MPG on a "good day".... now back to the regularly scheduled thread.
 

AJ.

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I had a 92 Dakota extended-cab longbox with a 5.2/overdrive ,4x4, and 3.91s. I crashed it into a guardrail on glare-ice. I miss it a lot.
65 was ~2100
 
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