Is the 8.1 still a dead end swap?

[Frankenchevy]

I’m crazy, but bear with me. I’m thinking about pulling the new nv4500 I just installed in my K30. For what I’m doing with it, I think I’d like to go back to an auto trans.

I still have my good HD th400, but I’m thinking 4l80. So I started perusing my local CL and found a 2001 2500 burb 4wd with 8.1/4l80e. It runs, drives, passes smog in NV, etc. 180k on the clock, asking $4500, but I’m sure I could get it for less with the current gas prices. I have plenty of space to part it out to recoup a fair bit of money.

1. Will the 8.1 fit as is, besides engine mounts and some crossmember adaptation? I’d like to run stock manifolds if I did this swap.

2. What do I need to do transfer case wise?

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[Dutch Rutter]

From everything I've read they are the same mounts and even exhaust patterns as a old school 454 BBC. One of the more internet known guys who's done this swap, put it in front of a nv4500 and really seemed to enjoy it. He did say there is not much aftermarket support for them but he was fine with that since it was more then enough in stock form. I'll see if I can find his info again, it was on a different forum but he did a lot of good detail through the process.

Edit: Here he is.

8.1L install into 1978 K10DONE - The 1947 - Present Chevrolet & GMC Truck Message Board Network

8.1L install into 1978 K10DONE The 1973 - 1987 Chevrolet & GMC Squarebody Pickups Message Board

67-72chevytrucks.com

 

[Frankenchevy]

Its looking like I’ll need the front drive from a van or medium duty truck if I want to run the AC up high to avoid notching the frame.

 

[Dutch Rutter]

Its looking like I’ll need the front drive from a van or medium duty truck if I want to run the AC up high to avoid notching the frame.

If it were me, I'd stay with your current nv4500 and t-case setup then plug the 8.1l in front of it and use a standalone ECU. Mainly for the simplicity and using what I already had. But if you do want an automatic, I've read that in 91 gm used a np205 behind the 4l80e in the crew cabs (pretty hard to find i bet). That would keep the front drive line on the passenger side.

I think (going off memory, so probably wrong) in Dirty Larry's build he used the serp belt setup from a van which held the AC high up.

Btw... you should let me know if/when you want to offload that nv4500

 

[yevgenievich]

Van accessories are not easy to find. But frame notched and reinforced correctly should be fine. Transfer case can be used as is with right adapter but will need modification to add a tone ring. Or simply use dakota digital converter

 

[Frankenchevy]

If it were me, I'd stay with your current nv4500 and t-case setup then plug the 8.1l in front of it and use a standalone ECU. Mainly for the simplicity and using what I already had. But if you do want an automatic, I've read that in 91 gm used a np205 behind the 4l80e in the crew cabs (pretty hard to find i bet). That would keep the front drive line on the passenger side.

I think (going off memory, so probably wrong) in Dirty Larry's build he used the serp belt setup from a van which held the AC high up.

I figured I could get my 32 spline 208 to bolt up to the 4l80 with the right adapter or spacer.

The NV4500 is a great transmission, but it’s a slow shifting truck transmission. I love the mannerisms of my nv5600 behind a Cummins, but I want something different for my square…

 

[Dutch Rutter]

I figured I could get my 32 spline 208 to bolt up to the 4l80 with the right adapter or spacer.

The NV4500 is a great transmission, but it’s a slow shifting truck transmission. I love the mannerisms of my nv5600 behind a Cummins, but I want something different for my square…

Thats is definitely one of the downfalls of the nv4500 behind a gasser. The diesels you don't feel it nearly as bad since they don't rev as high as the gas and they have all of that low end pull. But you are very correct, they are a big slow shifting truck transmission.

Yep, from what I've read on this swap. A 32 spline np208 will work fine. Im also assuming that keeping the np208 will let you keep your speedo cable. Unless that won't work/adapt with the 8.1l ECU, I have no idea on that one.

 

[Bextreme04]

I figured I could get my 32 spline 208 to bolt up to the 4l80 with the right adapter or spacer.

The NV4500 is a great transmission, but it’s a slow shifting truck transmission. I love the mannerisms of my nv5600 behind a Cummins, but I want something different for my square…

No adapter needed. A 32 spline 208 is a direct fit onto a 4wd 4L80e.

 

[Hunter79764]

The 4L80 should have an electric speedo output (VSS) that will feed the ECM the right information, and your NP208 should have the mechanical speedo cable to run your gauge just fine. I believe the Donor 'Burban uses the 4L80E VSS for computer functions and a secondary VSS for gauge readout, as well as diagnostics to make sure the transfer case is in Low when it is supposed to be etc. That is probably something you will need to have removed on the ECM tune, but I don't think that would be a problem although I haven't run into it directly myself yet. Most likely you would just change the parameters to a 2WD calibration segment instead of 4WD, which I think it a drop-down menu in HP Tuners. I'll echo my understanding that headers and mounts are same as old school, and you might have some looking to do on oil pans but I could be wrong.

I've got an 8.1L in my motorhome, and its a great engine so far. C5500 Kodiak based, 12' high, 8' wide brick has no problem cruising 75 (except for the mpg part). We pull the 87 3/4T suburban (in my profile pic) behind it and can hardly tell it's there. And by that I mean the acceleration is barely different, cruising is identical, and I have a hard time seeing it in my mirrors unless I'm turning

Be prepared for the MPG numbers you might get. Obviously my setup is very different from yours so my numbers mean nothing, but 6-7 MPG is my usual range for flat highway trips at 60-70 mph. You ought to be in double digits, but maybe not by far.

 

[yevgenievich]

Dakota digital adapter on the transfer case speedo output will allow stock speedometer to work. As well get the signal to the ecu. 4x4 4l80e after about 93 does not have the output sensor installed. Output of 4l80e is essentially same as th400.

 

[77 K20]

Be prepared for the MPG numbers you might get. Obviously my setup is very different from yours so my numbers mean nothing, but 6-7 MPG is my usual range for flat highway trips at 60-70 mph. You ought to be in double digits, but maybe not by far.

I had a 2003 Silverado 2500HD. Extended cab, long bed, 4x4 with the 8.1L. I kept hearing how bad gas mileage was- but it was from the Allison transmission equipped guys. Mine had the ZF-6 manual transmission. It made them a lot more efficient, and better power to the wheels.

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I use Fuelly and kept track of all my tank fillups. I primarily used it to pull my 21' 5th wheel. When towing I got 10-12 mpg. When running empty on a long highway trip it was 14-16 mpg.

I had the same gas mileage when it was stock vs when I did a BlackBear tune on it. With the tune it got rid of the stupid torque management. I did find I lost around 2 mpg when I used an ethanol blend of gas instead of ethanol free.

If I remember right GM detuned the 8.1L a bit when they put it in the Suburban and the Avalanche as they had the 4L85e? transmission.

 

[OldBlueDually]

Wow, that is one nice Suburban!! I would trade you for my '01 3/4 ton with the 6.0 if you want to send that 8.1 out my way and you could do a 6.0 swap instead

Honestly I would like to own a Suburban like that, some of the hills we encounter with our 6.0 I tell my wife "sure wish I had that 8100 right now"....

That would be a whole lot of engine for your K30!!

 

[Craig 85]

I’m crazy, but bear with me. I’m thinking about pulling the new nv4500 I just installed in my K30. For what I’m doing with it, I think I’d like to go back to an auto trans.

I still have my good HD th400, but I’m thinking 4l80. So I started perusing my local CL and found a 2001 2500 burb 4wd with 8.1/4l80e. It runs, drives, passes smog in NV, etc. 180k on the clock, asking $4500, but I’m sure I could get it for less with the current gas prices. I have plenty of space to part it out to recoup a fair bit of money.

1. Will the 8.1 fit as is, besides engine mounts and some crossmember adaptation? I’d like to run stock manifolds if I did this swap.

2. What do I need to do transfer case wise?

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Before you go disassembling that Suburban, if it's in good shape and not thrashed you can get about $11-12K for it. No I'm not on drugs, especially if it has 4.10 gears and no rust. My suburban is almost identical see below. I'm on a 2500 Suburban form and this a realistic price. People are looking for these constantly.

If you choose to remove the engine let me know, I need a couple of trim pieces.

My '01 2500 8.1L

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This guy on You Tube put an 8.1 into a Square body Suburban.
Pete's Place
https://www.youtube.com/c/PetesPlaceGarage

PSI bought the 8.1 from GM, they have different brackets for truck and bus use. Many U-hauls and Schwann's trucks ran 8.1L engines too.

Raylar Performance can build a 8.1L motor for you, but I would guess that would cost $10K +.

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[Hunter79764]

That makes sense on the transmission options, and yes, Torque Management is pretty severe on these. I've got the Allison in mine and have not made any changes to the tune, but it might be in the works. Keeping some of the TM in the tune for 4L80e and possible heavy duty use might be a good idea, unless you want to do a shift kit etc., or can just use good judgement on how hard you can beat on it.

 

[Bextreme04]

That makes sense on the transmission options, and yes, Torque Management is pretty severe on these. I've got the Allison in mine and have not made any changes to the tune, but it might be in the works. Keeping some of the TM in the tune for 4L80e and possible heavy duty use might be a good idea, unless you want to do a shift kit etc., or can just use good judgement on how hard you can beat on it.

4L80 won't need any torque management. Especially if you have even the mildest of upgrades like internal dual feed, sonnax line to lube valve, and mild shift kit would be more than enough to handle anything a stockish 8.1l could send at it.