First some History...
I have a '76 Crew Cab that I restored a few years ago. The original 460 / C6 was untouched as it only had about 58,000 miles.

Since then, I've put on about 10,000 miles. The motor is getting more and more leaks every day, starting to burn more oil, oil pressure warm is getting lower and lower, it's losing power, harder on fuel... I've done a complete tune up, it has a new carb that is tuned well so I think it is just time for the 37 year old engine to be rebuilt.
The transmission is not shifting like it used to. The torque converter makes a whining sound once in a while. I've replaced / adjusted the modulator, adjusted the bands, fluid and filter change. It's driving OK but it needs to be freshened up.

What I want out of this truck...
I would like to use this truck more and more as a 3 season daily driver. It drives nice, has the room I need, and has a coolness factor that nothing newer can match. I would like to use it to pull my camper which is about 7000 lbs.

Now the decision...
This fall / winter, I figure it is time to address the issue. I am not an engine / transmission guy so I will have to pay to get them rebuilt. I know this will not be cheap.

My cousin has a 1993 F250 2WD that he is done using. 351 / OD trans, about 70,000 miles, runs like a top. I can buy it for $800.

I am really leaning towards pulling the 351 complete with OD transmission and putting it into my crew. Aside from the wiring harness, the rest of the swap should be pretty easy and inexpensive since I have the complete donor available. I presently have the in cab tank that I want to ditch so having to figure out a rear fuel tank option needs to happen anyway.

I am looking for opinions. Rebuild the 460/C6 I have and still not have overdrive? Swap in something newer? I am after comfort, reliability, drivability, and some better economy. A 460/c6 will still be screaming at highway speeds. Can it be built so offer some level of economy? I would love to see mileage in the teens not single digits!!!

 

Time for a cummins 12v swap.

 

Rebuild the 460 it will probably cost less than swapping that 351 in and the power will be there. You are driving the wrong truck for good economy. It is possible to get 10-12 mpg out of the 460. The 351 will probably get the same mpg just strain more pushing that heavy truck around.

 

Thanks for the replies. I have been considering a Cummins swap since I ripped the truck apart 4 years ago. I have been watching and I cannot seem to locate a donor for anything close to reasonable $$$.

I realize this truck will never get great economy with a gas engine. I didn't think this truck would be all that much heavier than the F250 that presently has the 351. I don't expect it to pull like a 460 but it should be better than adequate, no?

I have 3.73 gears in the back. If I were to stick with the 460/C6, would swapping some taller gears help much or would I be sacrificing too much low end response / towing capability? Actually, I even wonder if changing gears is an option with the Dana 70 that is in there...

Is there anyone out there with an old Crew who does not have a larger displacement gas engine or diesel? How is it with a smaller V8?

 

Approaches to improve MPG: Engine efficency, driveline efficiency, and aerodynamic efficiency.

Rebuild the 460 and get a reman C-6. I figure about $2500-3000.

I'd consider a Gear Vendors Overdrive based on your description.

 

At the moment I have a 460, np435 with 3:73 gears on 35"s. I think I could actually go down to the next gear ratio but would have to use the granny gear to get moving rather than 2nd that I use now. So feasibly with the close to stock tires you have now versus my 35"s you should be able to drop down to the next ratio.

If you decide to rebuild the 460 think about a e4od or a zf5 manual out of a later model with a 460 also throw in an RV cam to eek out a bit more torque.

 

The 351 swap would be a pain. Lots of sensors, wires, computer, fuel pump, list goes on and on. You would need to swap rear axles too for the speedo sensor. Then the 351 is speed density so there really aren't a lot of mods you can do to them. The 460/C6 would be easier and cheaper. If you go to a 31 or 33" tall tire in the rear you would slow the rpms down a little.

 

NAPA offers a reman 460 at around $1650. That would keep the engine part simple. The 5 speed swap sounds like a great idea but I don't know what is involved.

 

Thanks for the opinions guys. I have awhile to give this some thought. I will probably rebuild what I have but have been thinking about the newer engine swap. I realize it is more work but thought drivability would be better with fuel injection and OD trans. Of course, once what I have is rebuilt, the drivability should be better too and have much more power!

 

Instead of rebuilding the c6, I would try looking into a newer transmission with overdrive. An AOD or e4OD would be some good choices but I'm not sure what's all involved in swapping.

 

From what I have researched, there is no inexpensive way to do this. The AOD would need to be a "built" unit then need the adapter plate to mate it to the 460. The E4OD would need a standalone controller which is also quite a few $$$ added on top of the transmission itself.

 

Instead of buying the truck with a 351 in it could you find a FI truck with a 460 and a E4OD in it? Might have to pay a bit more but then you would get OD, the power of the 460 and FI for best starting and efficiency. This would require a LOT of wiring and such but would make for a good combo for what you are looking for.

On a side note it is possible to switch the 460 over to MAF (mass air flow) style FI and to sequential injection (better low rpm efficiency) if you wanted to but again you are back to even more rewiring and it would require a tuning system for the ECM.

 

I've been watching for a donor truck to do this exact thing but no luck finding one. The wiring doesn't scare me. As long as a person takes their time and has the entire harness to begin with, it shouldn't be that bad. If I thought it might be too much for me to tackle, there are places out there that will take your harness and computer and strip it down to the essentials for you.

The good (if there is a good) thing about our winters is they are long which gives me a lot of time to complete whatever it is I decide to do.