First off let me say that this is just a hypothetical situation and not a for sure project that will ever flurish.

My truck is currently a 1999 F350 5.4 gasser with 4.56 gears and 4R100 4x4. One day I would like it to make it a diesel project truck when I have another daily driver. The dream is to have a diesel powerplant 400HP or maybe less with a ZF6-speed and of course 4x4.

Option A: 7.3 direct swap

Buy a complete donor truck, build the motor in the garage, and swap all desired components (wiring, just about everything in the engine bay, and trans, etc...) and be done with it.
The 7.3 is a great engine with some potential as a power maker, but requires alot of money and upgrades to get there. Not to say that the cummins would not take money to build, but for the same cost building a 7.3 you could build a more powerfull 5.9. atleast that is what I have gathered from alot of other build threads.

Option B: 5.9 12v cummins swap

I would be able to keep my wiring harness in the truck as well as the instument cluster, have an engine which is completely mechanical, and not have to worry much with sensors and other electrical BS which is associated with a powerstroke. With a little help from FordCummins I could have my ZF6 dream truck cummins powered with better possible mpg than the 7.3.

Either way I go I know I will be needing a SuperDuty IC and radiator, transmission and maybe t-case, floor pan cut out for the tanny, and all new exauhst. Another issue may be the low gear ratio's I have in my axles now. 4.56 gears are amazing behind that 5.4 but behind a diesel they are a little steep for 35"s. Correct me if I am wrong, but a v8 (7.3) handles the higher rpms better than an I6 (5.9). So with the 7.3 I may be able to handle the 4.56 gears, but with the 5.9 I may need to consider regearing since the power curve peaks at about 1900rpms. Having said all that I may still need to re-gear even if I had the 7.3 and would more than likely do an axle swap to a D60 front and Sterling posi rear (my truck is currently open diff.) with gears to match my needs.

Now don't hate on me for saying that I am considering a 5.9 swap and I know it would be more cost effective to buy a truck and sell the one I got. But what would you do between the two options? Just looking for opinions not debates.

 

I don't know much ... but I think the 4.56 gears w/ your 35" tires would probably be close to right for pulling.

I have a 2000 PSD. 3.7(3?) ratio. When I bought it, 35's were mounted. was great for empty driving. Not good for pulling. At 70 mph, the engine was turning 1600. 1800-2200 is the best range for pulling on the 7.3 (I do not know about the cummings)

What do you currently turn at 70 ... I imagine it's not far from 2000.

I went back to stock (265/16") and while it doesn't look as good ... it pulls a LOTTTA mo betta!

Al

Still haven't found the signature update!

 

By the calcs it should be turning around 2250 or so but my tach its more like 2350-2400.
I think that has more to do with tire wear and the fact that 315-75-16 is actually 34.6" tires so I am thinking that might be a little high for cruising speed in a diesel; perfect for towing though.

 

I vote Cummins. I the long run I think it would be cheaper to swap. My dream truck is a '05-'10 F550 with a Cummins and a 6 speed manual trans.

 

i have a 5.4 in my F350 and im wanting to do the same type of swap. After its all said and done it would be cheaper to just swap in the Cummins, buy a motor reseal it and buy the kit from fordcummins.com and be done

 

I don't know much about cummins besides that owners like them, but digital engine usually offers better fuel economy than the older technology.
You plan to drive the truck for long years, so initial cost will be secondary, while difference in annual fuel cost can be significant.
My both 7.3 are stock and I've been pulling 30,000 + lb combos with my F450 just fine. Would I love 400 HP? Sure I would, but spending $200-300 on fuel daily is not making me looking for increasing this part.
Would I have 60 grands burning my pocket, I sure would take newest technology with power AND fuel savings, but the World is not perfect and looks like you figured out this part already.

 

My personal vote is also cummins, but only because of the 12v. I would not even consider a common rail because if I did then I might as well throw a 7.3 in there in my opinion (they both require computers). The 12v is such a nice power plant because of its simplicity; it is like the old reliable ford idi's, but you can make late model power easier.

 

Hmmm.... just thinking aloud here with things to consider:

I have to ask about the 400HP. HP is really gasser-speak because that is in the upper reaches of the RPM band and cruising at high RPM is not a common practice. For power, I look at one number - torque. Gas torque peaks near the HP peak - at the higher RPMs. Diesel torque peaks at 1800-2000 RPM - a great cruising RPM. The mods in my sig (with links) were targeted at fuel economy because I drive 20K miles per year, much of it highway. In my chase for MPG, I brought the torque and acceleration up to the point that this beast is much quicker and a better puller on mountains than the 460 gasser I used to drive. I had no idea how quick my truck could be until I chipped. My injectors are stock with 1/4-million miles on them and my transmission is beefed up to where John Woods himself was quoted that this is a reasonable alternative (but not a replacement) to a JW or BTS. The 5.9 is revered in the diesel community, but it's old school. The 7.3, also revered, has that delicate balance of having just enough technology to really ramp it up - but not so much technology that it falls flat on durability and reliability. With my chip, I have the options of dialing for the driving conditions of the moment - on-the-fly. Either one will serve well, but the ultimate goals and cost to attain those goals make this a personal choice instead of a simple "This one is better than that one".

 

Yeah forgive my gasser spirit. Gas is all I have ever known until a couple of years ago when my brother started driving. He got an old 6.9 diesel f250 and it has been nothing but light diesel hotrodding since.

I figured with this thread I would be able to get some folks opinion on which one they would go with and why. I love the idea of both motors going into my truck and I think the deciding factor would probably be 7.3 heads or 5.9 tails. Flip that coin and see what happens.

 

Great post!

 

If you go with the 7.3, it would be easier and probably cheaper just to buy a truck with the Diesel already in it. However it would be very hard to find one with a stick.

 

This. I found one with a stick, perfect in every way - cab/bed config i wanted, nice wheels and tires, good price, etc. What turned me off was the bottle of stop-leak I found under the hood...

 

That's hilarious; My dad had a similar experience looking at a '01 Platinum F250. When he popped the hood one of the heads were painted a different color; only one.

 

When I was looking last fall I found a low mileage (59k) 2000 7.3 6-speed, only real issue for me was it was 2wd, truck wouldn't start on weak batteries, stop leak container under hood, had new clutch (59K...no towing either....?) No thanks.

 

Personally I vote for the cummins swap. I might take on this swap in a few years when I'm closer to finishing school and ill have more free time on my hands to be playing around with my truck.