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Justifying a 4bt swap?

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Location
Mount Laurel NJ
I am considering a solid 4L80E actually, and I saw they have 208's that can be mated to it. Do you think that it might be able to fit under the body tub without a body lift? Also, the cost of a 6bt varies heavily. A 6bt that was rebuilt from top to bottom will run about $11,500. Not cheap. But they have pullouts as cheap as $1500 in working order. Rough, but working.
 

red

Active member
1,988
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Location
Eagle Mountain/Utah
The 4L80E has been swapped into a bunch of trucks/k5s/suburbans of this body style without body clearance issues. So no need for a body lift or modifying the transmission tunnel. The 4L80E is basically a th400 with an overdrive, a locking torque converter added to it and a computer to control it unless you add in a manual valve body.

GM standardized their transmission ouput to a 6 bolt round setup in the mid to late 80's so as long as you have the right input shaft for the tcase they will bolt up. np203/205/208/241. Don't know if the allison has the same bolt pattern but I think so.

Can buy rough but running 6.2/6.5 pullouts for less than $200 or a brand new (not rebuild) P400 long block for $8000 with all of the 6.5 issues eliminated. I like Cummins engines but the dirt cheap price tag of the 6.2/6.5 is very hard to beat. New injectors for $50 each with no core charge for example. That's not including the military surplus stuff.
 
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Mount Laurel NJ
Thanks, I appreciate the input and knowledge. Here is what I have learned. *Hopefully useful to anyone reading this in the future* The np205 can attach to the 4L80e easiest, since some of them actually came with a 32 spline female input shaft. There are readily available adapters that will hold the figure 8 bolt pattern version to the round bolt pattern on the back of the 4L80e with a passenger drop, rather than the driver side drop found on the fords/dodges. If you end up with a 205 with the male 10 or 27 spline, you will either have to bite the bullet and sell it for a 32 spline female, or you will have to have the hole that the input shaft bearing rests in enlarged to accommodate the female 32 spline setup. Also, even if you were able to get it to work, the 10 spline is the weakest and will likely suffer or break with any diesel engine swap. If you were going a 6bt route, a 32 spline is almost a must for that 205.

That is what I learned over the years, and more so recently. Making an allison work is probably excessive and pricey. A 4L80e can take up to 440 ft lb of torque, which is the max of the 6bt from 1996-1998. If you purchase a 1st gen level 6bt, you are looking at a max of 400 ft lb of torque (stock), which is actually less than a nice 6.5 diesel, and probably a bit simpler. Heavier yes, and if you want that to work with especially an M1009, a strong crossmember (there is a guy selling custom ones on ebay) should cut it and you won't have to touch the firewall. But you will have to try and relocate as much as you can, mainly the batteries to the rear. That should equate to less strain than a stock CUCV with a plow. Oh, and better front springs or an add a leaf will help loads.

As for the transmission, does anyone know if the old crossmember tranny support could be of any use? Or will that have to be scrapped?
 
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Mount Laurel NJ
I have one more big question for those that are reading this. Regardless of the swap or what we choose to do, don't I have to convert to 12 volts? And if I do, I see that it involves keeping the two batteries (which is preferred actually) but what do I do about the single alternator that will be on the swap instead of two? Any advice??
 
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Barrman

Well-known member
5,254
1,761
113
Location
Giddings, Texas
4L80E to transfer case.

The CUCV trucks all had TH400 transmissions with a 32 spline output shaft. All of the trucks had either a NP208 or NP205 married transfer case. If you find a 4 wheel drive 4L80E with the pedestal/transmission mount bolted to the back of it. Then any CUCV 208 or 205 will bolt right up to the transmission. The 4L80E will bolt to any GM 6.2 or 6.5 that had a TH400 behind it without changing anything at the engine or flex plate.

However, the 4L80E is about 1.5 inches longer than the TH400. The stock CUCV cross member will have to be moved toward the rear axle 1.5 inches. By happenstance, that is exactly the bolt spacing on the frame rail of the CUCV trucks where the cross member bolts in. What was the rear cross member bolt hole in the frame now becomes the front cross member bolt hole. Bolt the cross member up with the front bolts and drill new rear holes with the cross member as the template.

Of course, the transmission shift linkage will have to be lengthened a few inches. So will the transfer case shift linkage. If you are not doing a lift at the same time. The rear drive shaft will need to be shortened and the front drive shaft might need to be redone longer.

The CUCV TH400 pedestal mount is cast iron. It will not bolt directly to a 4L80E. It is just a hair too big. Think SAE standard on the mount and metric on the 4L80E. The aluminum 4L80 mount fits the transmission and the transfer case. I did, just for fun turn a cast iron mount down with a hand file in a short amount of time to fit a 4L80E. I used the aluminum one because it was right and I had it.

Back to the 6.5, 4Bt, 6BT debate. The Cummins engines make more torque at a lower rpm than the GM engines. Dodge had a lot of trouble the first years of the 6BT keeping torque converters alive in their automatic transmissions. Same with clutches and transmission input shafts on the manual transmissions. That is why there is a diesel version of the NV4500 used by Dodge. The original version would break too easy.

I don't know who manufactured the Frito-Lay delivery trucks with a 4BT and TH400 in them. Just that when they were sold off at super low prices they became very popular. I would imagine they are where most of the available 4BT engines people can find at a good price today came from. Frito-Lay apparently had a massive TH400 failure rate in those vehicles. They went to the NV4500 I think because of it in the later ones.

So, yes a TH400 or its overdrive half brother the 4L80E can be bolted to a 4Bt or 6BT if you have the GM Cummins rear engine plate which is very expensive all by itself. Go over to 4BT.com and there are dozens of threads by people who have tried it. Most end badly for the transmission and the owners wallet.

Then there is the Charge Air Cooler needed to make the big power out of a 4BT or bigger power out of a 6BT. I wrote charge air cooler because intercooler isn't exactly correct or applicable to the three main ways of cooling the turbo charged air entering the engine.

The 1992 6BT Dodge trucks without a CAC and without a waste gate had almost the exact same hp and torque numbers as a Banks dealer option equipped 6.2 truck. The 1993 6BT got an air to air CAC along with another ring on the piston to handle the higher pressure. They had higher numbers than a Banks 6.2 which didn't have a CAC. Then Cummins went to the P7100 inline IP that could be turned up to make huge power. With the increase in power, the CAC kept getting bigger too.

There is not much room on a square body Chevy truck for an air to air CAC. Especially, with the engine oil cooler, power steering cooler, transmission cooler and condenser between the grill and radiator. People have done it though. Mostly with a 2003 Duramax air to air CAC modified along with some radiator modifications.

An air to water CAC can be made to fit under the hood without a bunch of large tubing under the hood. It does need a water tank, water radiator, a pump and the plumbing for it though. Most people that have used it say they are great for drag racing length runs but useless on a long up hill climb in 100° outside temps. Especially if you have 3 or 4 long climbs in a short amount of time. The water gets so heated it doesn't cool the air any.

Mist injection is another way of CAC with mist water or alcohol injection. There are some true believers on the internet out there. They use gallons and gallons of liquid getting squirted in above a certain boost or EGT. It works great, but a 50 gallon water tank in the back just isn't my thing.

The CAC discussion is there because without one, sustained power just isn't possible. No matter what super engine is under the hood. So, look at the numbers of a 1992 Cummins in a Dodge D30. That is probably the power level a 6BT in a square body truck will be at unless a CAC is added. With that in mind, is the extra expense, weight and labor of putting a 6BT in the truck compared to adding a turbo to the already in the truck 6.2 worth it?

4BT engines are priced so high with power numbers the same or below the 6.5 turbo with a 2,600 rpm redline that again. Is it really worth the effort?
 

Barrman

Well-known member
5,254
1,761
113
Location
Giddings, Texas
I started writing before you posted the battery question, got busy with my students and then finished after you had posted.

Cummins starters and alternators are available in 12 or 24 volts. I have never searched, but I am sure there are ways to mount a second alternator to a Cummins BT engine to keep the 12/24 system. The hard part will be the isolated ground for the alternators.

Any diesel will need 2 batteries for starting.
 
231
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Location
Mount Laurel NJ
Very good information here, thanks for being able to supply me with your knowledge, I really appreciate that. I am going to double check my options, and I still have a few more months to plan this all out correctly. As for the battery situation, I discovered that there was apparently a way to actually use one alternator with the dual battery setup in the CUCV, so if you wanted to just go the 12V route, it shouldn't be too bad, it's just that the information is a little limited on that.
 
231
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Location
Mount Laurel NJ
I know this question is going to be a shot in the dark but I figured I'd ask. Regardless of 4bt or 6bt, it seems like it can be done without touching the fire wall, but I wonder... will everything be alright with the transmission hump? Like in terms of without taking the body off the frame, will it be able to clear a 6bt/4bt bellhousing?
 

red

Active member
1,988
24
38
Location
Eagle Mountain/Utah
Before I had the wrecker I had a 87 crew cab k30, installed a 4bd2t and nv4500 into it. Complete frame off rebuild. Reinstalled the cab first then the engine/trans after it. Firewall and transmission hump was never touched with the 4cyl and nv4500. a 6bt is TIGHT front to rear and some people end up modifying the firewall for clearance.

IMG_20140506_145232_825.jpg
 
231
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Location
Mount Laurel NJ
So here is the thing. I talked to a guy that sells these custom cross members for 6bt/chevy on ebay about this swap. He claims that regardless 4bt or 6bt (I guess it depends on how you mount a 4bt) you will HAVE to pound in the bottom of the firewall on the bellhousing a bit, because you will not be able to access the bellhousing bolts that mate the trans to engine. Is this true? I want to still be able to remove the trans without having to remove everything in the event of potential future servicing. Did this happen to you?
 

red

Active member
1,988
24
38
Location
Eagle Mountain/Utah
I didn't have that problem. With the 4cyl you can move the engine forward if there is a clearance issue. With the 6bt though there is very little wiggle room.
 
231
5
16
Location
Mount Laurel NJ
Maybe one could hammer back some of that metal? I think you will have only about 1/2 inch from everything when it is all said and done if you did a 6bt. From what I heard you will have to slam that in, I just wonder if that affects anything with the tub itself
 

Chevyguy27

New member
3
0
0
Location
Warner Robins Ga
Summit racing sells the cummins to square-body chevy motor mounts, cross member, and trans adapter. My buddy swapped the 6bt into his m1008 with the motor mounts and adapter. It uses a powerstroke 6.0 starter.
 
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