Hi folks,
I've rescued an old worn out '91 F250 7.3 IDI 4x4 extended cab out of a farmer's weed patch. Now I'm rebuilding it, mainly for self-education purposes. This truck will just be a snazzy toy when completed - I have plenty of other Ford workhorses to do the jobs I need done.*

Along with some bodywork & paint, I'm rebuilding it mechanically, including rebuilding & possibly modifying the engine. This truck won't be doing any work, but I'm hoping to improve my fuel consumption as much as possible. I've already replaced the 410's with 355's; replaced the auto tranny with a 4 spd & overdrive. Does anyone have suggestions for engine modifications while I've got it torn apart?
Thanks in advance for any assistance offered.*

 

Turbo, cam and tune up.

 

Thank you!

 

if it's a 91, wouldn't you want the zf-5(5-speed)?

That being said, 3.55s with the OD in a zf would give you basically 60MPH at 1600RPM; good cruising speed.
I'll tell you right now that if all you're doing is cruising at 60mph, you'll get good mileage without a turbo.
If you intend to drive 70mph+, or 60mph with a load, get the turbo. I've not noticed any appreciable difference in fuel economy with the turbo with that gearing(because you're already in the peak efficiency band), but you get far more power and efficiency out of it in the 1800-2400RPM range.

 

Thanks for the tip regarding the different transmission. I just bought a '93 F250 to use as a parts truck (for engine, tranny, transfer case, & 355's), and it came with a 7.3 IDI & 4 spd & OD transmission. I haven't had a chance to look for the transmission you suggested. I haven't installed the tranny I purchased, so, if I find a better type I can use this one in another project.

 

are you saying its a 4spd with an auxillary overdrive, or that it is an overdrive transmission? The 93 should have the ZF5-s42 which is a 5spd

 

Any fuel mileage you get will be much better than the 11.4 I get in my '08 450. I wish I could get better mileage without breaking the bank. I've always been told the better it breathes the better mileage and performance you will get. By getting a free flowing exhaust, bigger air intake and a programmer you will increase both. I have a 6.4 so I dont think I can be much more help than that. Good luck and have fun with the project.

 

Manual shift transmission, **** says 4, then OD.

 

Thanks for the well wishes.
If it makes you feel better about your fuel consumption, my '86 F350 dually - 460, 5 spd, 410's - gets about 9 miles/imperial gallon, and my '89 E350 Cabriolet FI 460, 3 spd auto, 410's - gets 7.
There, doesn't that make you feel better?

 

If I find a zf5, I'll put that in my F250 custom project. This 4 & OD tranny can go in something else. I'm also working on cutting down the frame on a '93 F350 & removing the body, then putting my old Festiva on the frame.
(my medication has been checked & approved. Maybe an air quality check in here wouldn't be a bad idea...?)

 

A ZF5 has a shift pattern like:
1 3 (OD)
| | |
-----------
| | |
2 4 R
If that makes sense.
If it's got a total of 6 gear positions, it's the 5-speed zf-5. If it's got 5 gear position(4 forward gears + reverse) it's the earlier one without an OD gear.

I think you've got the zf-5 transmission, which is what you want.

 

I agree, sounds like a zf-5. Might have an aux od trans too if you have an extra shifter other than the trans and 4x4! Some use buttons instead to do the aux trans controls.

Ways to increase mileage:
Cut weight as much as possible

Improve airflow if at all possible - height can be a factor. A skid plate on the bottom might reduce some drag. Mythbusters did a test on tailgate up vs down, apparently up is better as the air gets trapped and circulates. If you've ever sat in the bed of a truck you will know this as all the crap flies around you, whereas it flies straight out the back with it down. I doubt a tonneau cover or canopy would help more. Either way these are basically bricks on wheels.

Free flowing intake/exhaust - cold ram air intake especially

Narrower tires for less rolling friction/weight. Plus proper alignment.

Turbo with ceramic coated pipes to keep more heat in. Lower a/r would help at lower rpms. Non-wastegated are less efficient I think because they will generate excess boost at cruising speeds.

Electric fans or no fans. Stock fan sucks for efficiency.

Use as few accessories as possible. Dont need ac?- take the belt off.

Just running, this platorm uses minimal electricity. But running all the lights, wiper and blower motors come close to the limits of the stock alternator. Dont know if the 3G alts are anymore efficient though. Swapping as many lights to LED could reduce the consumption some - the less an alt has to generate the less drag it has.

Injectors might change efficiency some. Diesel burns better when properly atomized versus old Dribblers/peeing injectors.

Proper timing can help.

I got about 17 when i went camping a few years ago. It was a little higher than that but close enough. Standard cab on 34" tires, banks nonwg turbo, tired 6.9, new BB injectors, dana 44 front. T-19 4-speed. Cruising around 65-70mph no idea on RPMs. Probably weight close to 6250-6500.

Could always swap it into a smaller truck - f-150 or something too.

If your worried about fuel costs, these engines will run off almost any kind of oil or fuel... Some people filter old motor oil or vegetable oil and run a mix of that with diesel - 50/50, 80/20, so on. Some even add some gas to thin it out. But there are cons to running that stuff too so ask around before doing it. The shorthand is it can wear the fuel system out faster and you'll want to do the return line kit for veg oil a its acidity can eat it up.

I think thats all correct, could be wrong.

 

Ways to improve efficiency:

Aluminum driveshaft, Turbo, LRR tires (the LRR tires work btw), tune up, synthetic lube, electric fan, etc. I put a lot of my eco mods on my signature.

Basically the best way to save fuel is to drive slower. Go 55 mph and you'll be getting excellent mileage.

I run WVO. Don't run a blend or BioD, they will destroy your system. Best plan is to run a separate heated WVO tank with separate aluminum fuel lines, with an aluminum heated filterhead (do not use the stock filter), and separate duralift fuel pump (do not use the stock pump). The veg tank should be aluminum (do not use a mild steel tank). Do not use any brass or copper or steel fittings. I've run my Jetta on WVO for 7 years without issue and my van for 35000 miles so far since Oct 2012. You need a good supplier and a good filtration and dewatering method. For more info, visit the biofuels section of this forum. The investment is high for a good WVO system, but once it's done, rolling on reliable grease is the bees knees.

 

This thread has been inactive for a while, but has some good info and suggestions in it. Basically the biggest gains are going to be from gearing. If you have an overdrive transmission and 3.55's your in a pretty good range depending on what speed you want to drive. Keeping the rpm's in the 1600-1800 range just above peak torque gives the highest mpg unless heavily loaded.

https://www.ford-trucks.com/forums/7...rs-thread.html

 

Another thing, changing the fluid in rear axle can help too