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Diesel swap for pure tow rig. Normal towing and best mpg options....?

shady

shady

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I'm going to do a dream build on my dually soon. And my main use will be towing my k30 or skid loader.
I'm willing and able to use whatever 2wd combo would be best to,
Get decent mpg when not towing (priority 1)
Able to easily tow 10,000# in normal terrain without beating it to death. (Stock 454 wasn't horrible, but not enough)

I'm not sure whether I'll end up manual or auto. Depends on what the best all around choice ends up as.

Current ideas are,

Gm 6.2ls/6l80
Gm 6.2ls/10l80
Gm 6.2ls/ nv4500
". " 5600

Vortec 7.4/ 4l80 (actually have these now)
". " Either of the manuals above

Lb7 dirtymax/ Allison. (rather do lb7 than the newer)

7.3 and whatever the best trans that comes behind one auto or manual.

Cummins of some sort and same as above for trans.
 
I keep leaning towards the vortech and 4l80 I have. But I want to be able to do Moab and other places without getting 6mpg or something close.
 
So I think going with what you have is a great starting point. The 6.2's LS engines are great don't get me wrong, but they are not stump pullers. They still need too many rev's to get the torque out.

The L29 is a great baseline. Roller cam block, decent heads. I'd take it further and bump it up with a better camshaft. It seems like every one I've driven gets moving quickly but runs out of breath in higher gears. Watch some of Richard Holdner's videos that he's done on L29s with changes in camshaft and heads. A good cam will wake up an L29 and going a little further put better heads on it to take full advantage of the cam profile.

I'd switch up from the stock L29 intake and go for a conventional 4bbl style intake converted to multiport injection run with a Holley terminator system for easier tunability than the black box pcm the stock engine had that is limited in its ability to handle changes.

Unloaded it still won't get better mileage than a non-emissions diesel like a 12v or LB7 though. It would probably be low teens for mileage if you optimized the gearing and tire size combo.
 
For your goals and parts availability, a 12V Cummins diesel would be my choice if you want a manual transmission (NV4500 or NV5600). If you want an auto find a 6 speed Alison transmission for it.
 
The cam and intake thing with a terminator is actually exactly what I was thinking lol.
But I was thinking a step farther and go coil near plug for full sequential mpfi.
Run a dual plane with the divider milled out for the longer runner length. Which should help down low. But keep the stock heads.


I do have another vehicle the 7.4 and 4l80 could work and be FUN in.... That I happen to need a motor and trans for. So really it's not a big deal if I don't use it for this truck. Which is what made me start thinking.
 
My only balk on the Cummins is that the older ones at least are just so damn loud.
Much louder standing next to the truck than the power stroke or Duramax in my experience.
Inside I'm sure it can be made ok, but fock they're noisy outside. Beyond that the Cummins is my favorite choice really.
A bullet proofed 7.3 or lbz should be quieter and just as powerful in mostly stock form I would think.
But it's hard to beat the simplicity of a 12v Cummins.

That's why I'm torn on the whole deal lol.
I'm willing to put out 10-15 k on my drive train.... I don't want to wish I did something else later.
 
shady said:
My only balk on the Cummins is that the older ones at least are just so damn loud.
Much louder standing next to the truck than the power stroke or Duramax in my experience.
Inside I'm sure it can be made ok, but fock they're noisy outside. Beyond that the Cummins is my favorite choice really.
A bullet proofed 7.3 or lbz should be quieter and just as powerful in mostly stock form I would think.
But it's hard to beat the simplicity of a 12v Cummins.

That's why I'm torn on the whole deal lol.
I'm willing to put out 10-15 k on my drive train.... I don't want to wish I did something else later.
Click to expand...
Having owned 2 Cummins trucks (06 and 93) and an 01 7.3 I don't think the 7.3 is any quieter and the fuel mileage is usually a little better on the Cummins. I've never owned a duramax but I've had a couple as work trucks.

Out of the options you listed I would recommend the duramax its going to be the best overall power/quiet/mpg. I don't the extra complexity of the 7.3 is worth it over a 12v Cummins, so the Cummins would be my next reccomendation. For the trans behind the cummins I would highly recommend a zf6 manual, in my opinion its much better than a nv4500/5600.

On the noise issue comparing my Ford with a 7.3 to the Cummins trucks I've had the 7.3 seemed quieter until the insulation under the hood came apart now its just as loud if not louder than the Cummins trucks so that might be something to look into.
 
Gas Towrigs are worthless in my world , the 50% reduction in fuel mileage and lackluster performance is just not something I’m willing to deal with.


So Diesel it is:

Forget the 7.3 , while it’s a pretty dang good engine. It’s not a great swap candidate and they don’t really have much power potential vs. dollars spent.

I would say the same thing for the Duramax as well. It’s easier to make big power with a D-max then 7.3 , but they are not without their quirks .

Allison Autos, if you are leaving the engine mostly stock then they are ok . But they are big and heavy and complicated. Once you start adding big power the Allison needs to be built just like the Dodge Automatics . Except the Allison is double to triple the price .

NV4500/NV5600/G56/ZF6
All great transmissions , price and availability would be my concern.

Probably stay away from the NV5600 it’s getting hard to find parts for them lately.

A NV4500 with a Gear Vendors overdrive is a really great setup.

5.9/6.7 Cummins , to me it’s really the only option . Yes the 12-valve and VP44 24-valves are loud . But honestly So is the 7.3 .

To get a “quite” diesel it needs to be a common rail with the pilot injection. But honestly with good sound deading and good cab rubbers it’s not bad in the cab.

The swap is cheaper and easier then a Duramax and the HP per Dollar ratio is probably double or triple .


In conclusion I’d go 12-valve/NV4500 with a gear vendors with a 3.73 geared rear end .
simple , tough ,and more power then you would need.

Distant Second would be a LLY/LBZ D-max with a ZF6
 
I heard the newer Cummins with the common rail were quieter, so that's sounds like a possibility. Seems Cummins is where this is leaning.

As for mods I don't really plan on doing anything except whatever is recommended for economy and longevity/reliability.

Don't need a 900 hp monster machine. Just more torque to mpg ratio than I have.
Any of them diesels will have around 500ftlb or more stock. Where as the big block will need work for that, and get less mpg because of it I think.


As for sound deadening, I plan to do a lot of that underwood and inside anyway.
 
Id say a ve pump 12 valve with a late model g56 transmission. Ve pumps are great on fuel and start so damn good. They run well and can get 600 ft/lb very easily and probably keep you over 20mpg.
Common rail does not fit in a square like an earlier Cummins does.
I am very happy with the noise level inside my k30 with pretty standard sound deadening.
 
obijuank5 said:
Id say a ve pump 12 valve with a late model g56 transmission.
Click to expand...

Agreed, if you are staying under 425-450HP then the VE reins supreme . It has Dynamic Timing . So they start easy and get better mileage then the P7100 trucks .

2wd VE pumped trucks are known to get 22-23 MPG empty depending on gearing and right foot application.
 
Right now I have 265/75/16"s and 4.10 gears.
I was thinking I could go with the 3.73's with the torque of a diesel.
I could always go down to the stock 245/75 if I needed a middle ground after the gear swap.
 
265 and 3.73 will be 1900 at 70 mph. Under 2000 is good for fuel mileage and over 2200 is tow mode. 4.10 are tow mode. This is considering a .74 overdrive ratio.
 
I dont know how some are getting 15+mpg towing 10k + through the mountains….My 06 LLY/6spd Allison averaged 9.5 for the whole trip to Moab and back. Power was not an issue, set the cruise at 75 and let her ride. It did downshift to 5th a few times going through CO. and pushed the temp up to 230, but then we would head downhill and let it drop down again. Point here is make sure you have a huge capacity cooling system and airflow is more than adequate. The quietness of the newer engines is nice for long hauls.
 
Should have bought this… @The Griff

IL - 94 12 Valve Dodge Dually

It absolutely kills me to do this, but this truck will only rot further into the ground sitting in my yard. 1994 3/4 ton 2wd Dodge, 12 valve Cummins, NV4500, 157k miles, $3500 or best offer. This truck was my dad's baby, the truck he always wanted, the one we took two trips through Canada...
ck5.com ck5.com
 
76zimmer said:
I dont know how some are getting 15+mpg towing 10k + through the mountains….My 06 LLY/6spd Allison averaged 9.5 for the whole trip to Moab and back. Power was not an issue, set the cruise at 75 and let her ride. It did downshift to 5th a few times going through CO. and pushed the temp up to 230, but then we would head downhill and let it drop down again. Point here is make sure you have a huge capacity cooling system and airflow is more than adequate. The quietness of the newer engines is nice for long hauls.
Click to expand...


I have never gotten single digit mileage in any of my Cummins powered trucks even when grossing close to 30k .

Speed has a lot to do with it , dropping from 75-70 mph can be 1-2 MPG difference. It’s one of the reasons most of the big trucking companies have their trucks governed to 68 MPH
 
My dad always complained about that governing thing in his semi. He said it made the average mileage drop a lot.

But back then I think they were doing it by cutting power somehow. Not with computers like today.
 
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76zimmer said:
I dont know how some are getting 15+mpg towing 10k + through the mountains….My 06 LLY/6spd Allison averaged 9.5 for the whole trip to Moab and back. Power was not an issue, set the cruise at 75 and let her ride. It did downshift to 5th a few times going through CO. and pushed the temp up to 230, but then we would head downhill and let it drop down again. Point here is make sure you have a huge capacity cooling system and airflow is more than adequate. The quietness of the newer engines is nice for long hauls.
Click to expand...
Yeah that's pretty low.... Not sure why it would have been.
I got 12.5 (return trip average) towing my k30 back from Eric's in a half ton with a 5.3 :dunno: .


Right now my dually averages about 9-10 regularly, and 7-8 towing heavy stuff.

Did 7.5 when I overloaded it and towed my grandpa's skid loader. Total trailer weight with that on was like 13,500 or so.
Did fine on them trips except one steep hill, where I had to down shift and do 40 lol.

If I could get 12.5 towing again I'll be happy enough.
Trailer weight and gear weight for what I'm planning should be in the 10k ish for trailer, and another 1500# of stuff in the truck by a rough estimate. About what I had with the half ton when I came back from erics
 
My 11,000 pound 06 dodge with a 400/850 tune, aurora 3000 and .79 ratio overdrive I still get 12 towing the blazer. Even back when it was on a 26’ gooseneck.
It’s a 15-17 truck in town.
It’s also 6500 dollars to fix it minimum lmao
 
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