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Discussion Starter · #1 ·
Hi,


I'm building what will be a rig I want to travel the USA with, but do some light off-roading to get to the good spots.

I have: an 05 express van, 6l LQ4 engine, 4l80e transmission. It says 3500 but has a 12 bolt rear. I have a 14 bolt from a 93 truck, or access to one from an 06 truck with disc brakes, but I know I'll have to cut and re weld leaf spring shackles because the van is slightly wider. I may wait until a disc brake 14 bolt van width axle appears.

I am rebuilding the engine, and transmission. I am extending the frame 20" to make it the "long wheelbase" express van. I have to cut the rear axle anyway due to the addition of a np214 transfer case.

After this, I have a large covered utility bed I got from an 80s era Ford van (van was scrapped) I will mount to the GM van frame. I'm a college educated welder, and decent with fabrication. I have a shop where I live.

I think the covered utility bed likely weighs a half of a ton, give or take.

I also purchased brackets from Timberline, to convert it to a 4x4, using the gm 9" differential I have, for an IFS (relax, I'm not going to rock crawl with my live-in rig. I don't need a solid axle rig I might roll. I plan on putting 4 of my industrial solar onls on it for 1,600 watts, 12v inverter freon climate control in the box, ham radio, 12v fridge (I have an 80l fridge\freezer), toilet with septic, I'm shooting for 40 gallons of fresh water with full pressure pump, electric folding bed\sofa, sink, workshop, drone launchpad, sun deck with ballistic glass sunroof, mood lighting, swivel TV, swivel propane oven\stove so I can cook in almost any position including outside, full dvr and 180 degree cameras, possible directional cell booster antenna on an x\y axis, 6kwh of lithium polymer batteries, 4 individual mppt charge controllers and a 3kw pure sine wave inverter, as well as a small propane on demand water heater, winches front and rear, and possibly air lockers, front and rear. This will be my second rig I've built with similar specs)

That said, I looked into 3.08 gears, as 85-90 percent ofy driving will be long distance highway.

I don't want to lug my rig, but I am willing to sacrifice some off the line performance for the sake of better overall fuel mileage. I don't want to overstress my transmission as if I'm towing a trailer at all times, either. And, I don't my need engine spinning at needlessly high rpms at 65-75 mph. I also don't need super low gearing, as if I need more guts off road I'll just shift into 4 low. I just want to get into the cozy camping and scenic spots. But not get 4mpgs getting there.

I wonder if 3.08s will be too tall, but I've heard the 4l80e is geared very low, so maybe it evens out?

I also wouldn't be surprised if I'm carrying over 2,000 lbs in the utility bed alone with my tools, batteries, water, ammunition (have to be prepared for the invading Chinese Russian Nazi communist gay Italian Zionist zombie gothic transgender-fluid werewolf alien (if I left anyone out I apologize) apocalypse, like every other red blooded American patriot!)

It's starting to sound to me like 3.08s are too short, but I also don't want to shoot myself in the foot on the highways, either.

My girlfriend will have a schoolie soon I'll be helping her turn into a live in tour bus, if anything happens to her rig I can tow it in 4 low, plus if anything happens she can ride with me, so towing won't really ever be an issue. If I can't fit something in the rig I'll just put it in storage.

Partly the reason my rig is going to be so well powered and capable is so I can assist in an emergency, if decide to. But light to moderate off-roading will likely be part of my journey.
 

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Discussion Starter · #3 ·
Figure out a tire size and punch all of your info into a gear calculator.
That is a legit idea. I, perhaps, also need to ask myself, what tire is good for fuel mileage foremost, and perhaps light off-roading second. (if at all. My first live in camper van was 2wd, I had to clear paths, winch in, and winch out of the best spots I've ever been to. Spent weeks in paradise, sometimes. The 2wd van has 15 inch rims and low cost street tires. But I made it work. I'm fairly decent with 2wd vehicles off road at this point)

My van has 16" rims, any suggestions? As narrow as possible? Any deficiency off road can be helped with the winches, digging, high lift jacks- but I don't really plan on getting too crazy with the rig. I may sell it as an apocalypse vehicle, depending, when I am done with it. So the less damaged it is the better.
 

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blatant asshole
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Lol. 3.08, gas motor, 10-11000lbs and off road tires!


Depending on tire size youre gona want 4.56/4.88.

You will be bogged down foot to the floor 24/7 and that will eat 2x as much fuel as spinning 3k @ 1/4 throttle.

With rpm drop work load goes up.

3.08s are for cars, 1500s, and stock diesels.
 

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blatant asshole
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And you sure as shit arent gona get 3.08 for a 14bff. 3.21 was the fastest.

Your stock axle is a dana super 60 hence the 12 bolt cover.

Very few heavy axles were ever able to use faster than 3.42.

Youre also going to need to match your front gears. So you need to look at whats available for it.
 

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Discussion Starter · #7 ·
Lol. 3.08, gas motor, 10-11000lbs and off road tires!


Depending on tire size youre gona want 4.56/4.88.

You will be bogged down foot to the floor 24/7 and that will eat 2x as much fuel as spinning 3k @ 1/4 throttle.

With rpm drop work load goes up.

3.08s are for cars, 1500s, and stock diesels.
Are you sure the effect would be that dramatic? The engine makes 300-330 hp\ 360-370 lb ft, and the transmission is also geared pretty low... Judging by the heaviest 05 express, 6,000 lbs, plus 2 more is 8,000 lbs. You may very well be right.

I wonder how big of an mpg difference all terrain tires would make vs street tires, vs aggravation off road, if the fuel difference is worth the hassle.
 

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Discussion Starter · #8 ·
And you sure as shit arent gona get 3.08 for a 14bff. 3.21 was the fastest.

Your stock axle is a dana super 60 hence the 12 bolt cover.

Very few heavy axles were ever able to use faster than 3.42.

Youre also going to need to match your front gears. So you need to look at whats available for it.
All very good points. I did, however research it, the gm 9" front has a 3.08 kit available as well as the same for the 12 and 14 bolt.

I may try 3.08 at first, the move to 3.56 and see what real world difference it makes. I don't want to swap out diffs as it's a pain in the ass, which is why I'm hoping some real world people chime in, here.

When I was a kid I remember people crying about the terrible fuel mileage of a 4x4 vs a 2x4. But, the only real difference is differential gearing, as far as I'm concerned, as adding 250 lbs of hardware would kill fuel mileage as drastically as I heard (and assumed).

I thought, why not gear your 4x4 for highway driving? Use 4 low for climbing off road. In my mind getting street mileage from a 4x4 was possible.

I have a 1983 Isuzu pup truck that is unstoppable off road but gets mid to high twenties fuel mileage, almost 30 during a long trip. I also have a 1984 gm square body 4x4 1500 with the 6.2l Diesel, I tuned it and got the same mileage as the pup, almost 30 mpg.

Why can't I get good mileage out of my gas 4x4 rig, too? Well I can try. And I want people to know, so if I survive, I want to give real world answers. I'm just trying to minimize my pain in the meantime

Also the Dana super 60 appears to be a front axle, the 12 bolt is rear, the front will be the gm 9" ifs
 

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blatant asshole
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You dont have a 12bolt. 12bolt stopped existing in 1984.

Super 60s comes in fronts and
........van rears.

4l80 are not "low geared" the are 2.48 1rst same as most other gm trans. They are a th400 + od. 700r4 is 3.00 1rat bit a pos 1/2t trans



14b 3.08s are for semi float h2, esclades, and trailblazers.

You can try, but failing is a better teacher.

Ive rebuilt over 2000 diffs. Ive installed and removed a few dozen geavendors, i have had 4x4 of a few styles.

For your boat anchor brick on wheels, over gearing will take the work load off the motor.

Your izuzu weighs 3500lbs
Your 84 is a DIESEL and like i said, 1500, weighs about 4500/5000.

You are not comparing the same vehicles in any way what so ever.

You keep calling the front a 9". Its not, its a 9.25"
 

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blatant asshole
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Go look at what a h2 gets for mpg. Cause that the closet thing your going to be able to compare it to.
 

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Rolling Mod
04 Wrangler Unlimited, 67 F100
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All very good points. I did, however research it, the gm 9" front has a 3.08 kit available as well as the same for the 12 and 14 bolt.

I may try 3.08 at first, the move to 3.56 and see what real world difference it makes. I don't want to swap out diffs as it's a pain in the ass, which is why I'm hoping some real world people chime in, here.

When I was a kid I remember people crying about the terrible fuel mileage of a 4x4 vs a 2x4. But, the only real difference is differential gearing, as far as I'm concerned, as adding 250 lbs of hardware would kill fuel mileage as drastically as I heard (and assumed).

I thought, why not gear your 4x4 for highway driving? Use 4 low for climbing off road. In my mind getting street mileage from a 4x4 was possible.

I have a 1983 Isuzu pup truck that is unstoppable off road but gets mid to high twenties fuel mileage, almost 30 during a long trip. I also have a 1984 gm square body 4x4 1500 with the 6.2l Diesel, I tuned it and got the same mileage as the pup, almost 30 mpg.

Why can't I get good mileage out of my gas 4x4 rig, too? Well I can try. And I want people to know, so if I survive, I want to give real world answers. I'm just trying to minimize my pain in the meantime

Also the Dana super 60 appears to be a front axle, the 12 bolt is rear, the front will be the gm 9" ifs
you can’t get good mileage because it’s a gas vehicle. A friend of mine just took a four-wheel-drive express van with a 3 L diesel on an extended trip through the Pacific Northwest. (Quigly) It’s barely got 20-25 mpg. You’re talking about a much bigger heavier vehicle with a gasoline engine. You will never see that efficiency. For what it’s worth he had a 6L80. A gasoline engine will never get the fuel economy of a diesel.
 

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All very good points. I did, however research it, the gm 9" front has a 3.08 kit available as well as the same for the 12 and 14 bolt.

I may try 3.08 at first, the move to 3.56 and see what real world difference it makes. I don't want to swap out diffs as it's a pain in the ass, which is why I'm hoping some real world people chime in, here.

When I was a kid I remember people crying about the terrible fuel mileage of a 4x4 vs a 2x4. But, the only real difference is differential gearing, as far as I'm concerned, as adding 250 lbs of hardware would kill fuel mileage as drastically as I heard (and assumed).

I thought, why not gear your 4x4 for highway driving? Use 4 low for climbing off road. In my mind getting street mileage from a 4x4 was possible.

I have a 1983 Isuzu pup truck that is unstoppable off road but gets mid to high twenties fuel mileage, almost 30 during a long trip. I also have a 1984 gm square body 4x4 1500 with the 6.2l Diesel, I tuned it and got the same mileage as the pup, almost 30 mpg.

Why can't I get good mileage out of my gas 4x4 rig, too? Well I can try. And I want people to know, so if I survive, I want to give real world answers. I'm just trying to minimize my pain in the meantime

Also the Dana super 60 appears to be a front axle, the 12 bolt is rear, the front will be the gm 9" ifs
You may hate to hear this, but you seem to be quite concerned about fuel efficiency and you are about to build this huge vehicle with massive weight. Being from Texas where folks move livestock, everyone who ever does that swears a diesel is the only way to go. Just something to think about. You may be fighting physics, and physics is undefeated.
 

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Discussion Starter · #15 ·
You may hate to hear this, but you seem to be quite concerned about fuel efficiency and you are about to build this huge vehicle with massive weight. Being from Texas where folks move livestock, everyone who ever does that swears a diesel is the only way to go. Just something to think about. You may be fighting physics, and physics is undefeated.

The back end came off of a Diesel... I should have kept it.

What about gas? 4.11 is the way to go? 6.14 is better and a 12\1 ratio is ideal. Run 12,400 rpm at 55 mph because it's gasoline. Yeah. Baby!

Diesel engines are heavier, more expensive to fix and more expensive to fuel. The initial cost of fuel in my opinion is not worth the offset in everything else. It also stinks to high hell.

I guess I have to find out for myself

Nothing but anecdotes here. I may try 3.08 just to succeed or fail.

My rear end is a Dana 60, 12 bolt, used in
Automotive tire Motor vehicle Helmet Automotive lighting Vehicle

modern vans only.
 

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blatant asshole
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Edit/deleted.


You know what. Fuck it.
Document this riot to the fucking penny then post mpg and 0-60.
 

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The back end came off of a Diesel... I should have kept it.

What about gas? 4.11 is the way to go? 6.14 is better and a 12\1 ratio is ideal. Run 12,400 rpm at 55 mph because it's gasoline. Yeah. Baby!

Diesel engines are heavier, more expensive to fix and more expensive to fuel. The initial cost of fuel in my opinion is not worth the offset in everything else. It also stinks to high hell.

I guess I have to find out for myself

Nothing but anecdotes here. I may try 3.08 just to succeed or fail.

My rear end is a Dana 60, 12 bolt, used in View attachment 3125204
modern vans only.
 

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Well, Thomas Edison was famous for trying things to see if they worked or not. Sounds like you may need to give it a shot. I think folks were making suggestions to help you take the next step to discover how well your plan might work, before you spent a lot of time and money to put it into action. Not everyone wants or even needs to do that to move forward. I will say, I think the vision of how your rig will look sounds great!!
In your previous post you mentioned some concern for achieving gas mileage with your rig. One way to get some potential insight on what it might do is to compare similar weight vehicles with similar engine/transmission combinations and that will get you in the ballpark. If your target vehicle is 10-12K pounds, then you might compare a Chevy 2500 or 3500 pulling a trailer with 6-7K pounds and then ask around or some forums what sort of mileage they see in actual usage. Also check there rear end ratios and tire sizes. This approach costs very little to learn a lot and set your expectations.
Also gas engines produce their power higher up in the rpm range, so as soon as you encounter some grade or a headwind, then more rpm is needed. I see you list a Toyota RV in your signature line, so you may be well versed in exactly these dynamics. You then pretty much know things work pretty well on a calm day on flat roads, but get a bit more challenging as the terrain steepens. Anyway, give it a shot and see how it works.
 

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Gm LS motors like rpms. 6 liters are gutless in 2500 pickup trucks with 4.10 gears.do not consider going any higher than 4.10,4.56 or lower would be better WITH STOCK VAN TIRES.this heavy van will be terribly slow and have horrendous fuel mileage no matter the gearing. Don't believe me? Load 1500-2000lbs in the back of it as is and see how it does.you will hate it.

"Rebuild motor and trans" "regear, rebuild and swap axles" are a lot of up front cost before you even start on the tiny home stuff.and won't even work that well when done.

Sell this van and get one with a duramax. it will in no way smell like the detroit,have more power and better fuel economy
 

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^^^ exactly, sorry but I have to smile at your "plan". Stock or slightly bigger tires, 6.0L , 4L80, 12k pounds.....and what 3.08 (where have you seen 3.08 for a 9.25" GM IFS?)........I have a strong suspicion it won't work well. Look at any truck from the OEM, when it needs to move or haul some weight.....there's gears!! If they could get a gasser/4L80 to haul around 12k lbs, get 20+ something mpgs, all with 3.08 gears.....I think it would've been done.

Oh, and it's D60. It's NOT a 12b.....
 
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