Looking for the Unicorn... Better highway MPG out of a 78 FJ40

[1969FJ]

The cummins r2.8 is considered the way to go. To bad diesel fuel is much higher than gasoline negating the savings.

 

[1911]

Swap in an H55F and split case. Find a 79+ rear axle for the parking brake.

Just FYI for anyone looking for a rear axle with a parking brake, you'll have to find one that was made 8/80 or later - up 'til then, the parking brake was still on the (one-piece) transfer case.

 

[orangeyz]

If you are actually getting 14 mpg with the 2F, then the picture for fuel economy payoff with an R2.8 is pretty ugly.

It will pay off for me at closer to 70,000 miles because I'm comparing it to a 350 that was getting more like 8 mpg

 

[POPO AGIE]

Right now for me the price of diesel only is an issue for my Ram 3500 or my John Deere tractor. I am sure the price will stabilize before I can drive my 40. I have diesel in two different tanks that I paid for years ago.

 

[sogncab]

The cummins r2.8 is considered the way to go. To bad diesel fuel is much higher than gasoline negating the savings.

I would go another route than the 2.8 if I were to do it again. But, brainwashed Cummins fanboy gotta do what brainwashed Cummins fanboy gotta do.


I did it for range more than anything.

20-21mpg is pretty consistent for me

 

[POPO AGIE]

I would go another route than the 2.8 if I were to do it again. But, brainwashed Cummins fanboy gotta do what brainwashed Cummins fanboy gotta do.


I did it for range more than anything.

20-21mpg is pretty consistent for me

I did too because the F motors and stock tank my range was very limited so between the R2.8 and the 29 gallon tank I may have more range then my Ram 3500. But have not been able to test the theory yet.

 

[ginmtb]

I had this made hopefully people chill if they’re stuck behind me while going slower to maximize MPGs lol.

 

[White Stripe]

For fuel mileage on a 2f you will need the carburetor dialed in well at both cruise and acceleration in regards to air fuel ratio. I have an air fuel gauge added to mine. I would probably run a stock carburetor rather than a holley carb. Vacuum advance will also need to be working. A efi kit added that does ignition timing control will make it so you can program those parameters rather than do mechanical adjustments if that's what you prefer. A free flowing exhaust will also help efficiency. With 31s for tires I would run 3.70 differential gears. 14 to 17mpg is doable with a 2f. It just depends how much effort you spend dialing it in.

 

[77mustard40]

Well tuned 2F that's never been cracked open and has plenty of blow by, rebuilt & recurved FJ60 dizzy, clean stock carb and I’m getting 13-15 mpg… and I don’t care. It’s getting harder each year to outrun my bladder.

 

[JohnnyC]

@ginmtb

I resorted to this on mine… the mass pike they ride your a$$ otherwise

It could just be the NY plates as they think all NYers are Yankee fans

 

[cruiserkev]

Did something similar to JohnnyC on my homemade tailgate. Only run it in the summer when the top is off and the ambulance doors are removed, fitting for what is essentially a tractor anyway I think. King of the slow lane!

 

[Chamba]

I bought a Chevy Duramax 4wd 4 door and tow it with that: much better fuel economy that way.... but no where near as fun.

 

[jayp2]

One other note, as you are chasing 1 or 2 MPG's consider how much fuel you can buy for the mods you are making to pick up those couple MPG's.
Here's the math to back that up: At 150 miles per week at $4/gal fuel if you go from 14 to 16 mpg you save $278/year. It's going to take years at that rate to pay out any significant modification to get those 2 mpg's.
Buy a used small car, that's likely a better use of funds. Save the 40 for weekends.

For the money you would put into the 40 to try to make it more efficient you could likely buy a used corolla that will get 40 MPG and go 300k with nothing more than regular maint

 

[Living in the Past]

The H55F and split case with 3:1 low range was more then I paid for the 40 new in 1978. The parking brake can still be used with the split case. If you have the 4 speed case and let the builder know they can build the TC to accept the parking brake. All the parts are off the shelf and still available.

The H55F requires a cross member that the 4 speed does not have. But I kept the mounts for the bell housing and the cross member under the transmission.

For me it was already in my rebuild plan to upgrade to a 5 speed and split transfer case behind a diesel.

There is a lot of support available for converting to the H55F.

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Few things about converting to a H55F. It requires a 10/82+ split transfer case. Those have a provision for a fifth gear oiler. As for a crossmember the four speed had them since 8/80. 10/82 the shape of the crossmember changed. Curve under the front driveshaft was deeper because the back of the driveshaft is further back. The frame on the 9/72+ FJ40 with an F engine barely has room in front of the torque tube to fit a H55F without a hand brake on the back of the transfer case. 10/82 when the H55F started it was never installed on the LWB. Those the hand brake remained on the back of the transfer case with a three or four speed transmission. Besides the cost of the transmission there is a lot of little details that figured out ahead of time can prevent surprises during the conversion.