I have kept my 1979 F-250 4x4 in barn for many years and its a gas guzzler. Anyone ever done a conversion to a 12 valve Cummins. Mine is still a nice truck and still would rather drive it than my 19 f350 but just uses to much fuel. Wondering what I could expect on fuel mileage. Mine has 3:54 gears auto trans.

There is a poster here that did a Cummins swap into a 79 Crew cab. It was sweet and he had a good thread you can search for but I believe he sold it a while back. Good luck

$4k for an engine.
$1k+ to swap?


10mpg to 20mpg.

10,000miles

1000gal gas x$2.80= $2800
500 gal dsl x $3.40 = $1700

So, you might recover $1100 per 10k miles.

40 or 50k miles to break even. Bet you won't drive that in
decades if it's a barn dweller. Plus, if it now get 12 or 14 mpg,
your payoff just got worse.

I love the torque and performance of a Cummins12v, many
who are used to gas engines don't like the turbo lag, and
high torque/low horsepower profile.

Always hearing how Chevy or Ford diesels are better, just
because they are more like what car drivers are used to.

Thanks Kid, will see if I can find his thread.

Is your 79 a V8 or I6? If perchance it’s a 6 cylinder you could put a 4BT Cummins in it relatively easily if you could find an old Frito Lay truck or UPS truck with one in it. They were about the same power as the 300 six but can be easily turned up and they last forever and make decent mileage.

Acesneights had the cummins/Ford.

You should pm him.
I think he liked the result, but Igor the impression he
wouldn't do another.

And his was an awesome truck.

It’s pretty pricey unless you are very resourceful and handy. My neighbor got one of a school bus and I think has the motor now in its second or third home . May wanna Check bolt pattern on your Ford drivetrain.

Mine is a V8 351m with c6 auto that I have found is not a good choice of trans for fuel economy. I will most likely put truck in my shop and do the engine swap just need to visit with someone who has done it to hopefully eliminate some mistakes along the way.

I’d talk to Tim Meyer about building a good 400 using his parts in your block and heads. Properly tuned you can see 14mpg with the C6 and reasonable sized tires. Plus all of your mounts and accessories are there, no junkyard searching or fabricobbling stuff up. Tim is the only place making good parts specific to the M blocks and really knows those engines.

14mpg would be almost double what its getting now. Its gets 9 on highway and 8 just running around.

Hig's ford was pretty sweet.

Here is the for sale thread: https://www.24hourcampfire.com/ubbthreads/ubbthreads.php/topics/12113476/1

And the "build" thread: https://www.24hourcampfire.com/ubbthreads/ubbthreads.php/topics/6037641/1

Unfortunately pictures are blurred by photobucket in the first and gone from the second.

Thanks cwh2. I remember the sale thread now. The build tread answered some of my questions already.

I wouldn't do it again, but it was fun.

Shoot me a pm if you have more questions.

Glad to help out.

Will do after the holiday weekend.

Thanks

Considering something similar myself, a friend replaced a 460 with a 12 valve in a 92 with the OEM 5 spd, he gets 23 mpg @ 70 mph. I have a 90 Cummins with Dana axles, only drawback is the original 3 spd auto.

I have seen MANY 76-79 F 250s both stick and auto and have NEVER seen one get anywhere near 14 MPG no matter what was done to them or which engine combo was used, mine got 11 with headers, a good intake, carb and cam designed for economy, that was IF I didn't get it over 65 on a flat road, a 12 valve would definitely get you there and likely into the 20s but a lot of work it would be!

My buddy’s son had a mid 90s Powerstroke. They bought a school bus with a Cummins and had it swapped. Their money, so who am I to judge. Can’t see how it penciled out.

You tube it. Couple of good ones there.

I think Higbean did that conversion also.......
Local guy I run into here once in a while around town, has a 74 or 75 F 250 4 WD,,,,

his sons, own a diesel repair business in town...

they had one of those IVECo's trucks brought into the shop that had been totalled, the customer just let the vehicle go..

when Dad's old 390 finally went with 300K plus on it, they pulled the IVECO engine out and trans and put it in the F 250...

He's got alike a 50 gallon after market tank on the F 250 due to the old 390 camper special....

he ran the vehicle up to Bellingham WA to visit his brother and made it all the way back to Roseburg before he had to fill it up.....worked out he was running 24 mpg or so on it.. and that is what he still gets with it....

due to the age of his truck and where he lives in Oregon ( no EPA inspection), it doesn't have the DEF crap on it...
Lewss HO over the 390 4 Barrel, but it makes up for it in torque....

I think that IVECO engine is a 6, but I really don't remember, as the last time I saw one its been quite a while...the vehicles are certainly around enough.... commercial vehicles.

saw this after I posted, sorry Higster...

There's no way you're doing that swap for $1k,

I know your's is a 3/4 ton but, are you running the stock motor?

I had a 78 F-150 with a 351M/4-speed trans and a 79 Bronco with a 351M/C6 auto and it was a tale of 2 motors. The 79 was stock except dual exhaust. It was plenty fun for a 16-17 year old kid. But, It got about the same gas mileage as you're getting.

My 78 which I did an amature resto on, was a different tale. It had mild cam of unknown specs, (stock valvetrain) otherwise, stock distributer, new plugs, wires, filters, an edelbrock 4bbl carb and intake, headers, and dual exhaust with no name glass packs. After that it got a legit 14mpg.

Mine is stock except for RV cam and dual exhaust. Has c6 auto with 3;54 gears and on a good day straight down interstate at around 68mph it gets close to 9. Be hard to add 5 mpg to that.

Might be money ahead to get a gear vendors overdrive.

I've sure thought about it with a 95 F350 flatbed dumptruck I use. I get 5-6 mpg every day in that pig, and gutless as hell to boot. I don't think I could get 7mpg if I through that POS out of an airplane from 40,000 feet.

A Cummins would sure make a good truck out of it. Only reason I haven't done it is I have a pto for the dump body running off the Ford auto trans and I wouldn't want to keep the auto. Don't want to lose the pto as it cost a couple K when I had it installed.