Swap 6.9 or 7.3 for a 460 in 75' F350 crewcab dually?

[blthomas]

Hey there.

Been searching the site looking at particulars related to swapping the engine in my truck.

I bought the truck to haul my Jeep on a flat deck, and occasional RV towing. Lately, I've been working the truck hauling scrap, doing some side jobs, and in general staying busy helping my Dad who has a half ton, I pull his tractors around (old antique stuff).

That said, the 460 pulls great (out of a 84' RV with a C6 and around 66k on it), but obviously the fuel usage is of concern.

I started researching a ZF5 swap to help with when I'm not towing, that would give me a overdrive, and during towing maybe I could pick up 1 or 2 mpg over the old auto.

Then I started reading here seeing that a IDI with a turbo and some minor tweaking should be able to pull just as well as the BBF, and probably out perform it in the mileage catergory.

I'm not super diesel savvy, thoughts on goign this route? I can handle fabbing the motor mounts, trans mount.

I would think my tanks would be fine after draining them.

Are the electronics tough to sort out? What about speedometer? Mine is cable driven now.

I have a 3.73 LS rear, I think that would be a great rear for both economy and towing with a ZF and IDI.

What kind of mileage could I expect not driving it hard? I tend to cruise 60ish on the highway loaded or unloaded.

Right now I'm around 6 with a heavy trailer, 8 with a full bed or light trailer, and maybe 10 empty. Guess it could squeak towards 12 empty, downhill, with a tailwind and Jesus pushing me along, but I doubt it.

Thanks for any input or advise on doing this. Not sold yet, but seriously considering it.

Blair

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[Devon Harley]

I would do 7.3 that's my opion with the zf would be a great combo and yes with a turbo and and moose pump you would have a stronge dependable good mileage rig I would say 14 towing 16 to 19 unload since u gt a dually if your capable of fab work do it it will be alot of work would be worth in the end by far diesel is about the only thing that makes since these days

 

[Keeway]

nice truck to start with. but a idi would be right at home in there

 

[Iowa 73]

Depends on how long you plan to keep the truck, and how many miles you put on it. Assuming you get a 4 mpg increase and it costs $1500 to do the conversion, it would take 18,000 miles for you to break even. After that it saves you money.

 

[blthomas]

You know I thought I was savvy with a calculator. What is a real world number for a truck like mine moving down the road unloaded with a IDI, zf5 and 3.73 gears?

If it's only 4mpg at best in difference then maybe I'll stick with my original plan for now with dropping a ZF5 to the gasser motor and see how it does. I'm using it alot, but probably only actually running it around 5k per year, since it's always on a weekend, and it's not every weekend at that. And this is the 1st season I've run it much at all. Maybe I need to crunch more numbers.........

 

[jhnlennon]

If your only putting on 5k miles a year, its probly best to stay with the gasser(unless your going for the cool factor or something). It would take quite a while to recoup costs if thats the sole reason your doing it, not to mention the time and aggrevation spent figuring everything out.

From my experiance towing heavy with an IDI i was always around 12 mpg. In a dually crew cab truck like yours, empty your gonna be around 14-15 mixed driving. An IDI costs slightly more to maintain, and replacement parts generally cost more and are harder to find. They are also little more diffulcult to work on than a carb'ed gas engine, and require a little patience and knowledge.

That being said, they will get roughly TWICE the mileage when working than a big block, and they are the cheapest of diesels to work on.

Either way, it costs money to run these big trucks anymore, its just a fact of life.

 

[Olb Blue Beast]

I plan on doin the same thing (cept w/ a 77' supercab Camper special). I'd go w/ a 6.9l idi & a ZF5

 

[SHARPIE]

Talk about a bunch of Debbie downers...I say go for it I'm in process of doing a diesel swap in my 78 as we speak, Changing the tranny will not increase you fuel mileage already been down that road but I was looking for the granny gear and overdrive in my old Bronco got 10 before and got 10 after but I could drive 70 on the highway so it was worth every dime...With a big truck and a 460 8-9 MPG if your lucky and dont bother with putting on a after market fuel injection tried that too waste of money...

Most posts I have read about fuel mileage is 16-18MPG is avg so thats a 50% increase in mileage in my book that makes it worth it alone, With a IDI there is no electronics except the transmission if you go automatic then youd need the E4OD controller,If you do stay below 93 (I think) It will have the VSS on the tranny If you go above then youd need to swap the rear end too, I got a complete truck so I dont have to go digging through junk yards getting nickeld and dimed, The only thing is you need a gear reduction starter other then that its not too bad.

Just look for my tread its all in there.

 

[bike-maker]

I took out a perfectly good 460/c6 out of my truck to replace it with a 7.3/zf5. I did it because I had my heart set on a diesel and manual trans. I did the math, and when you factor in the higher maintenance costs of the diesel, the diesel is hardly cheaper to operate than the gasser. I figured it would take about 10 years to pay for itself, and that's using the truck as a daily driver.
Now if you have access to waste motor oil for free everything changes......

 

[blthomas]

Thanks for the heads up on costs bike-maker. I've played with a calculator a couple times trying to get some good hard numbers.

I appreciate everyone's info and input as well.

I haven't bought a IDI or anything yet. I've run the truck alot, I would say it's 6-8 pending load. I never think to write the mileage down while driving.

I feel like 10 is a honest number unloaded with the c6. I never run it hard, many times trying like hell to keep it revving low.

I think the biggest obstacle with me heading one way or the other, is I can't find a IDI with a OD tranny anywhere local for a good price. That definitely puts a ding in my plans.

Unless I can get one or a whole truck cheap enough, it definitely will keep the project held up. Again, thanks for all the input and advice. This site is a great resource.

 

[franklin2]

I do not know how a 460 would react to the zf, but I swapped out my c6 behind my 7.3 for a zf, changing nothing else, and gained 3mpg. I was getting 12mpg, and now I get 15 mpg. I have 4.10's, 4inch lift and 35 inch tires. If you get overdrive, you won't believe how quietly it cruises down the interstate, keeping up with everyone else at 70mph+.

 

[GOOSE]

I have 4:10's, 33" tall tires with a front add a leaf, and squeak out 15 mpg's around town consistently. I think your lower 2wd truck with smaller tires and 3:73's would do slightly better. 12 is a good number for towing. Put a turbo on your "must have" list. Also, guys with a brownie or gear vendors get up to 14mpg's grossing 18,000lbs and 20 empty.

 

[chevytaHOE5674]

With my old bronco I went from a C6 to a ZF and went from around 10mpg to ~14mpg afterwards.

 

[blthomas]

Yea I find it hard to believe I couldn't get another mile or two per gallon with the ZF5 behind the BBF. Got several aquaintances telling me I'll see no change and even the thought of switching to diesel is also a bad idear.

I'll mull it over as much as I want dammit. ;p

I found a 6.9 with all new pump, injectors, glowplugs, with a Zf5 behind it couple days ago.

Waiting on a reply to see where it comes in price wise. All he has to do is call me back.......

Thanks for the input so far.

 

[blthomas]

With my old bronco I went from a C6 to a ZF and went from around 10mpg to ~14mpg afterwards.

Gasser or a diesel convert?