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LS swap, ECM and wiring ??

B454rat,

Like Russel said, $500 is a steal for all of that! The way I have the gauges set up in my old square bodies is no different than how they were originally but on a newer truck like yours gets more complicated but not difficult.

Keep in mind, the 8.1L was used in the 2001/2002 3500-HD truck backed by an 4L80E or NV4500. The 3500-HD was a GMT400 just like your Tahoe. With that, I would recommend finding a factory GM service manual / diagram for that truck to help you repin your current harness to work with the 0411 ECM on the 8.1L. If your real lucky, you might even find a 2001/2001 3500-HD in a junk yard and use the entire harness from the bulkhead on. In fact, there was one CL here in CO about a week ago that was a rolling 3500-HD chassis being parted out that had an 8.1L originally but I can’t find it now. If it helps you at all with parts searches here is a VIN of one of those GMT-400 8.1L trucks > 3GBKC34G61M101958

As far as a harness goes, I’ve never been a fan of reworking harnesses but if you got your hands on a 3500-HD harness that would be the cat’s ass for a quick and easy install. Of course, if you used the Allison that would require some modification as the 3500-HD was not offered with an Allison, only NV4500 and 4L80E.

This GUY did an 8.1L into a 97 Hoe which is pretty much what you’re doing. While I don’t agree with all of his processes he recipe seems to have worked out in the end. He is also a member of the 8.1L Facebook group. Might look him up with questions. I can’t remember his name though…. Jake??

BTW…this is what a 3500-HD with a 8.1L looks like. They were a bit larger than a 1 ton with an I-beam front axle mounted to leaf springs. 2wd only although there are some 4x4’s that were converted by upfitters that are harder than hell to find. Cool trucks
001.jpg


An 8.1L in a 3500-HD
Flatbed-Trucks-Chevrolet-3500-HD-5358805.jpg


Good luck!
 
The yard that has the engine has a coupe HDs, but neither were the 8.1, but diesel. Sold 4 wheeler tires I had laying around, so now I at least have a deposit to hold the combo. This isn't gonna be an overnite swap, as I want to tear the motor down and take a looksee inside. I might be sending you many PMs Larry!!!
 
A friend of mine who buys and flips cars and trucks for a living bought a late 90's or early 2000 Chevy dump truck ( 1 ton?),4wd, that has a 8.1 and either a 4L80E or an Alison in it...came with a Henniker minute mount plow..

He paid less than 2 grand for it--it is a bit rough as far as rust on the cab floors and rockers,and the dump bed,but its built like a brick s***house..was wishing I could have made him an offer on it--it has a weird skip that coils and plugs and an injector failed to cure--he sent it out to another guy 6+ months ago to fix it,and hasn't gotten it back yet..
I've seen an 8.1 in a Suburban not that long ago,around the same vintage,all original--never knew they offered them in a Burb..
 
Post KOH there is another 8.1 conversion waiting here....

8.1 plus NV4500
IMG_1194-L.jpg


Plus 65 Apache
IMG_1195-L.jpg


Plus other things :), should equal some fun.
 
I got bored one nite searching c-list, and found a couple 4wd 3500HDs with the 8.1 and 4500. Can't remember where they were but were stupid expensive too. I missed out on one years ago, not gas but blown diesel, but 4wd and 4500. Had a huge plow and a wing plow. Looked like a mini DOT plow truck....I'd love to have 8.1 liter, tranny no big deal, but 4wd crew or ext cab flat bed....
 
Just read that post the Larry linked. 32 pages!! Wow, now my eyes and head hurts. But after reading it, looks like the toughest part is the wiring. But I think the best and easiest is to get the aftermarket standalone harness. Also if he got it to pass in CA, no reason it won't here in NY. But I know people lol. He also went with the 4L80 (4l85 close enough). Not sure if I want to stick with the Allison or go with the '80. I know 80s are a dime a dozen, and everyone tells me the Allison is worth some coin, but I like the idea of having a "bullet proof" if you will tranny.
 
4l80 with simple upgrades can support 800 plus hp. Would still be cheaper than an Allison. I can destroy a stock Allison with an 8.1 and a hot tune. Bullet proof is not usually associated with that trans.

Wiring wise. We are $650 to convert a stock harness and performance tune. When I typed converted I didn't type hack it together. Harness is stripped, cleaned, inspected, shaped as needed, cloth taped and terminated with a 5 relay 10 fuse block that controls the harness, pump, fans and a few extra things you may need.

Nothing wrong with a brand new harness but there is nothing wrong with a GM engineered one either.

There is some awesome tech in that thread! There is also tech not in it that isn't easy to come by. The tuning side and overall potential of the 8.1. Yeah yeah, a lot of places claim the tuning is turning off codes and tq management. That's cool but that's not a tune. After KOH I am doing the swap shown above. I'll start a thread on it, show the basic swap.... If you guys want, I'll get heavy on the tuning side. Just let me know. Its not getting a cam but I can get into cam tuning. I saw issues in other 8.1 threads with cams.... That's an easy fix.
 
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Can you rewire the stock harness from an Allison to the 4l80? I can get a local tune for $300, but if you can do it all for $650 I'll go that route....
 
If I dont' get screwed on taxes and can get motor before too long, I'll send the ECM and harness out and have you do your magic. What all can and do you do to the ECM? I guess EGR is deleted on newer ones, that will make for a little more room and easier install, Evap BS, and guess there are only 2 O2 sensors. The simpler the install the quicker it may go!!
 
Team208Motorsports said:
After KOH I am doing the swap shown above. I'll start a thread on it, show the basic swap.... If you guys want, I'll get heavy on the tuning side. Just let me know. Its not getting a cam but I can get into cam tuning. I saw issues in other 8.1 threads with cams.... That's an easy fix.
Click to expand...
I'd love to see as much detail as your willing to type. I love learning new stuff. :)
 
b454rat said:
If I dont' get screwed on taxes and can get motor before too long, I'll send the ECM and harness out and have you do your magic. What all can and do you do to the ECM? I guess EGR is deleted on newer ones, that will make for a little more room and easier install, Evap BS, and guess there are only 2 O2 sensors. The simpler the install the quicker it may go!!
Click to expand...

Harness will be down to bare needs unless you need emissions in your area. You will need a VSS for the trans to work. Thats easy as the 4l80 can run input and output in the trans itself.
 
ashman said:
I'd love to see as much detail as your willing to type. I love learning new stuff. :)
Click to expand...

I have no problem showing what I am doing..... Final numbers will be different but at least you guys can see whats gong on this way. Hows your rig doing?
 
Wish I could do it sooner!!!! I miss my big block truck. Didn't matter what size tire, it would still light the tires up. right not I can't on wet pavement going around a corner. I think was the wiring is taken care of, the rest sorta seems like an engine swap. Some people make it more difficult than it needs to be. Other thing, I know this motor ran good, but has 200k on it. I don't want to go thru with the whole swap, only to pull the motor later cause it's tired, smokes, blows up whatever. So once I get it, gonna tear it down and look things over. Does anyone know rebuilding these? Does it use same bearings and stuff as a regular big block? I hate getting "kits" cause they give you more than you need or not enough. Want to do it right the first time, don't want to pull the motor if I don't have to.
 
I have not built one personally, so I cant answer that. I do know when swapping, if it sits for any amount of time. Pull the injectors and rail, clean them very well.
 
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