Learn me: Efficient torque converters

I'm working on my ramp truck, trying to make it not suck. 1990 F-350 351w, C6 auto, 4:10 gears, 32" diameter tires. The one time I bothered to calculate fuel economy, I managed 11mpg carrying a car. I understand that's pretty fantastic for an old Ford, but that's probably a standout occasion. I feel like I do worse with it most of the time and I want more.

I've looked into swapping to an E4OD, which isn't cheap, likewise putting a ZF5 in would require a fair bit of work and expense. For a lot less money, I could get a lower stall torque converter and save what I'm going to assume is about 2-300rpm at highway speed. Not near as much as an overdrive transmission (with a lockup torque converter no less!) But I'm looking for some gains. Does anybody have any experience with swapping torque conveters for better efficiency?

I had 79 Panther platform LTD with a mildly modified 302 and a C4. Rear gear was 2.26:1. Road trip car. 

I had the C4 rebuilt with a set of wide ratio gears (marketed as poor man's overdrive), and bought a special low stall converter, I think from TCI (not sure, it's been 27 years). It's selling point was as a fuel saver. 

The new converter would brake stall about 200 RPM higher than the stock one. Mileage from the whole thing dropped a bit (as in worse).

Based on my experience, I recommend you save your money for a transmission swap, or do the smartest thing, and don't touch it.

If the converter nets you 2 MPG, which I would consider unlikely, and costs a couple of hundred dollars, plus your time (as well as the "while I'm in there" tax), you still have to calculate how far you need to drive it before you're ahead financially.

I have to agree with Floating Doc here.  Unless you can find a cheap E4OD you're not going to get much in return.  The first year for them in trucks was 1989. The early models were best as they were "stand alone" I.E. they didn't need any electronic connection to the vehicles ECC. Later one are of course more common and a better trans but need to talk to a computer to work.  Baumann makes a stand alone controller for these transmissions. I looked at doing a swap on my '88 E250 van with the 5.8L C6 combo.  I didn't drive it enough per year to ever offset the cost of the swap, and this was years ago when fuel cost more then it does now.

But it's only money so just ask yourself: What will I spend for "X" amount of gain and how long will it take to be save that much in fuel?

I agree on using an E4OD. I wonder if you could use the 7.3L IDI diesel controller and harness as it was standalone. The Diesel E4OD won't work, bellhousing pattern is different.

So I've actually got the whole efi swap, harness, computer, MAF and all that from a 95 bronco. I plan on putting that on the engine at some point, and I'm fairly certain it was attached to an E4OD before I got it.

Apart from buying a used trans in unknown condition, rebuilds aren't terribly cheap I'm coming to find. Should I start looking for a zf5?

With 4:10s you're probably well enough above the converter stall rpm at your normal cruising speed that lowering the stall speed isn't going to gain you any efficiency. 

I honestly wouldn't do anything short of the trans swaps, and even then I wouldn't expect to ever even touch 13mpg unless this thing never breaks 55mph. 

3.73's?

Meh... 3.73s likely won't do much either.  You'll be slower and need more "foot" to maintain speed.

With the torque curve on a stock 351, you'll probably get the best MPG at around 1800 on the highway, but your trans will constantly be shifting.  2000 rpm should be the sweet spot.

With heavier towing and bigger vehicles, gearing isn't the main cause of your MPG.  Efficiency is.  You're moving an 8000 lb brick through the air.  Focus on efficiency losses.  It takes X hp to maintain your speed.  A gear swap might work on a Miata, but not really on a pickup.

Efficiency losses:  belt fan, not having torque converter lockup, tire friction, aerodynamics.  no smoking gun here.  You're just going to chase little things with big dollars and get not much in return.  Making a gas truck good on fuel is like trying to take the calories out of a donut.

If you REALLY want to save money on fuel, the answer here is a diesel swap, but how long will it take you to recoup your costs in MPGs?

And, honestly... I had an 88 TBI chevy that barely got 9 mpg towing a 7500 lb trailer, and even empty with a cap/topper/camper on the back, 13 empty was a really good day.  11 mpg loaded is really pretty good.

This might sound stupid, but... 5.3 aluminum LS + four speed auto swap?