2000 K2500 8.1 Swap

[00CrewCab]

Starting this thread off with questions. Got a 2000 K2500, CCSB, 454 4l80 4WD W/ electric transfer case. I’m wanting to do a 8.1 swap, and keep it as OEM/factory as possible. How I plan to do this is use parts from 01-02 3500HD “classic” cab and chassis truck, as these few models came with factory 8.1’s in the GMT400 platform. My question(s) comes in here, what all do I need to pull from the “donor” truck? Or what all OEM parts would I need to source from said truck. I’m assuming I’d need the following:
-Engine harness
-Computer (I think they can factory with 0411 pcm from my research)
-Front accessory bracket(s)
-Front accessories
-Cooling system(?)
-Fuel system(?)
-Engine mounts(?)
-Flywheel and starter

What else would need to be swapped over? I believe (and correct me if I’m wrong) those GMT400’s W/ 8.1’s came with 4l80’s, so is there anything I’d need to swap over for my 4l80? My donor engine will be coming from a 2005 3500 Silverado, is there any engine components or engine electronics I would need to swap to fit the 01-02 gmt400 platform design? To my research only thing I would need to fabricate is exhaust and possibly intake tube if I can’t find one. Any other input will be appreciated.

Reason I’m doing this swap instead of rebuilding my 454, cost (and fun), in my area, the cost of finding a good Gen6 454 would only be slightly under the cost of finding a good 8.1 and all supporting pieces. A good 454 is 1800-2500 used in my area, a good 8.1 is 1000-1500, and using salvage yard parts I could get the rest for 500-1000. And why not rebuild the 454? I’m not a fan of how much it lacks in performance from factory, it’s a dog IMO towing or not towing, low rpm and high rpm, and building a performance version to match the stock 8.1 would put me around the same cost or more than doing a factory 8.1 swap. And in the future I can modify the 8.1 to my liking.

Again any input is appreciated so input away, thanks all!

 

[b454rat]

I have 2 of the same trucks as you. I haven't driven the one yet but the other up n down the road. I can tell it's tired, but it will still lite the tires up. I had a 97 that would it effortlessly. It towed awesome too. I haven't messed with the 8.1, but heard they are a good engine, but parts are kinda hard to find and expensive. Forget performance, Raylar is the only one and they are extremely proud of that when you buy from them. But I'd rather build the 454, it would be cheaper and easier (since you have it, and don't need to swap anything over) and can get more out of the 454 over the 496. I think there are 2 companies that sell an intake, Raylar for one, and the other is a carb'd intake. I plan on making mine a 489, with the 0411 and some other stuff. Should be a good runner....

 

[Schurkey]

Keep in mind that the 8.1L is practically all metric for bolt threads. The bellhousing bolts, exhaust manifold bolts, motor-mount bolts, etc. are all metric.

Flywheel/flexplate is neutral-balanced. I don't know about the damper.

And of course, there's the difference in firing order which won't be a problem if you use the 8.1L wire harness--but could be an issue if you didn't re-wire the coil and injector harness from the 7.4L.

 

[00CrewCab]

I have 2 of the same trucks as you. I haven't driven the one yet but the other up n down the road. I can tell it's tired, but it will still lite the tires up. I had a 97 that would it effortlessly. It towed awesome too. I haven't messed with the 8.1, but heard they are a good engine, but parts are kinda hard to find and expensive. Forget performance, Raylar is the only one and they are extremely proud of that when you buy from them. But I'd rather build the 454, it would be cheaper and easier (since you have it, and don't need to swap anything over) and can get more out of the 454 over the 496. I think there are 2 companies that sell an intake, Raylar for one, and the other is a carb'd intake. I plan on making mine a 489, with the 0411 and some other stuff. Should be a good runner....

Not aiming for high performance numbers with the 8.1, at best a mild custom grind cam, and a supercharger. Which if I’ve done my research right there is one company that makes one. Or I’m not afraid to have a custom intake built for one of the “off the shelf” 6.0 ls superchargers or something similar. I won’t be getting rid of my 454 at all, I’ll be rebuilding and making a twin turbo engine for another project down the road. From my experience the 8.1 is more reliable, and a much better running compared to an equally built 454. Plus I’m also doing this for the fun factor, plenty of 454’s have been built, and plenty 5.3 and 6.0 LS’s have been thrown in these trucks, and the few 8.1’s I have seen have been mostly hacked together, I’m aiming for as oem as possible with mild upgrades. Eventually getting a built 4l80 or figuring a way to get a ZF6 to work with my electric transfer case. Big plans for the truck but first I want to tackle getting it into an oem 8.1 build first. I’m just not a fan of the 454, I’ve had two this one being my second, the first truck was 2wd with I believe 4:10, and I couldn’t spin the tires on wet roads. This one has 4:10’s for sure, and it’s such a dog, it can’t hardly spin the tires on gravel. Maybe I have just really worn out trucks, but my 305 sbc could spin the tires through second stock, ext cab long bed is what it was in so not a light truck. Not sure what gears it had though. I’ve also had a 8.1 4l80 combo before, was a 03 crew cab long bed work truck, could blast the tires off like it was nothing.

 

[00CrewCab]

Keep in mind that the 8.1L is practically all metric for bolt threads. The bellhousing bolts, exhaust manifold bolts, motor-mount bolts, etc. are all metric.

Flywheel/flexplate is neutral-balanced. I don't know about the damper.

And of course, there's the difference in firing order which won't be a problem if you use the 8.1L wire harness--but could be an issue if you didn't re-wire the coil and injector harness from the 7.4L.

This is why I’m trying to do it as “oem” as possible. Trying to use as many 01-02 gmt400 parts as possible. I looked a bit more into the harness and computer issue, and found that the 01-02 uses 0411 pcm from factory in the gmt400 platform. Also some 01 trucks got the 4l80 where as some 02 trucks got the Allison trans. So I’ve figured when it comes to mechanical parts I’m going to search 01 and for electrical I can search both 01 and 02. At least based off the limited research I’m able to find. Seeming the 8.1 is all metric, I wonder if the 4l80 that was used with them was the updated 4l80 rather than the one I have, either way the bolt patter should line up, I just need to find the correct bolts themselves. Or I may just swap over all the electronics I can pull and upgrade to the Allison trans, my only concern comes with the transfer case, I’d have to update/upgrade to the newer one, which I have zero idea if it’s even possible, seeming I haven’t been able to find any 02 gmt400 8.1 w/ Allison’s and 4wd. But again I may be searching for something that doesn’t exist because I haven’t been able to find much info on these trucks, let alone a specific combo on an already limited truck. But that’s the love of creating something special, especially when it’s getting built as if it was oem.

 

[L31MaxExpress]

01-02 8.1L vans were 4L80E backed as well. Even the 6.6L Duramax had the 4L85E in some vans. They all bolt up the same. The 8.1L flexplate is the same regardless if it has a 4L80E or Allison. Same 6 bolt converter pattern. The motor mount and bellhousing bolts are easy. The wrecking yards are full of them, grab them off the ground around a LS truck. IIRC my starter bolts are also LS bolts, bolted the old 350 PMGR starter right on the 8.1L. If you want to swap to high mount brackets, you need the accessory brackets, water pump and crank pulley/harmonic dampner off of a GMT400, Van or RV. My understanding is the Kodiak brackets and crank pulley are different though. The GMT800 water crossover is the same as the GMT400/Van but the Kodiaks are different as are some RVs. The correct one places the thermostat outlet slightly outboard of the driverside head. If you can find a newer 8.1L like 2005+ snag the timing cover, cam sensor amd timing set as well. The early cam sensors are discontinued and not serviced by anyone. Save yourself the headache and update to the newer parts. The newer one use a Gen III LS sensor and I doubt those will go away for a while. Before you stab the engine, hose down the crank sensor with penetrating oil where it goes into the block, remove the crank sensor and lube it really well with antisieze before re-installing it. They rust into place and can be impossible to remove without removing the transmission.

My 8.1Ls are all GM minus the headers. One has the 454HO/Base 502 cam and the other has the 8.1L HO Mag cam. I used the stock GMT400 8.1 air box and intake tube on my Tahoe, then switched it out to a custom 4" tube with a cartridge style LS7 MAF. If you find a GMT400 3500HD, get the PCM bracket and pedal as well. I would also grab the AC manifold hose set and canister purge line. 8.1L with either of the cams I am running, long tubes and a tune is a ~450 hp engine with 550 tq. That 450 hp comes in at a nice ~5,000 rpm and torque peak around 3,000-3,500. The 454HO/502 cam makes a bit more grunt down low than the 8.1 HO cam but the HO cam is smoother running and the torque curve is a bit flatter through the midrange with its wider LSA. Then there is the aound difference between the firing orders. I am more of a 1-8-4-3-6-5-7-2 kind of guy.

 

[Road Trip]

I’m just not a fan of the 454, I’ve had two this one being my second, the first truck was 2wd with I believe 4:10, and I couldn’t spin the tires on wet roads. This one has 4:10’s for sure, and it’s such a dog, it can’t hardly spin the tires on gravel. Maybe I have just really worn out trucks, but my 305 sbc could spin the tires through second stock, ext cab long bed is what it was in so not a light truck.

00CrewCab, the factory horsepower ratings wouldn't explain the dramatic differences
in performance that you have observed. Possibly the disparity is because the factory
ratings are based on healthy examples? Check this out:

* '96-'00 L29 7.4L (454) = 290HP / 410 ft-lbs torque

* '01-'03 L18 8.1L (496) = 340HP / 455 ft-lbs torque
* '04-'06 L18 8.1L (496) = 320HP / 420 ft-lbs torque

(Source: dieselhub.com article LINK)

Who knows? You may have been unfortunate enough to have driven not 1 but 2
wounded warriors? My '99 C2500 is no lightweight, but it pulls hard on the onramp,
and effortlessly continues towards triple digits. In English, the drivetrain seems to
have much more headroom than my wallet does. :0)

FWIW I've also driven a 305ci/5-spd GMT400, and it was a night & day difference.
The 305 felt like I was always driving uphill, whereas the 454 feels like I'm always
driving downhill. The difference is not subtle.

Don't get me wrong, I'm not try to call you out at all. Given the numbers above, if you
were used to a happy 454 punching out it's rated 410 ft-lbs of torque, and then managed
to swap in a '04 8.1 putting out it's rated 420 ft-lbs of torque, I don't think the difference
(stock) would be all that much to write home about. Sure, it would be great engine bay
eye candy at the local show & shine, but the 'back dyno' (ie: how far you get pushed into
the seat at WOT) might be in for a disappointment. (Especially if you were to also use
the Allison? Possibly moving from the 4L80-E to Allison accounts for the net loss in HP
& torque between the '01-'03 vs '04-'06 offerings? The Allison is made for long lasting
with severe service, and my understanding is that is takes more HP to run the
transmission itself?)

****

If it helps any to understand where I'm coming from, I started messing with BBCs ever since
a buddy bought a worn out 6 year old '73 Camper Special with a 454/Turbo 400/4:11 and
we rebuilt it to pull harder than new: (Misspent Youth)

To summarize, I'm not trying to talk you out of this at all. Actually, if the 8.1L engine was
the proverbial flagpole on a freezing day, I'd be the one to triple dog dare you to see if your
tongue would get stuck to it. :0)

Seriously, if you go for the 8.1 make sure to pick & choose carefully so that you will have no
fear of an old mild-mannered white-haired dude showing up in a dark blue truck and keeping up
with you...or at the very least making it a 'too close for comfort' race at the local drag strip.

Instead, do your homework & make me afraid to drive in Kansas. This would make for a terrific build
thread for all to enjoy & learn from!

 

[00CrewCab]

01-02 8.1L vans were 4L80E backed as well. Even the 6.6L Duramax had the 4L85E in some vans. They all bolt up the same. The 8.1L flexplate is the same regardless if it has a 4L80E or Allison. Same 6 bolt converter pattern. The motor mount and bellhousing bolts are easy. The wrecking yards are full of them, grab them off the ground around a LS truck. IIRC my starter bolts are also LS bolts, bolted the old 350 PMGR starter right on the 8.1L. If you want to swap to high mount brackets, you need the accessory brackets, water pump and crank pulley/harmonic dampner off of a GMT400, Van or RV. My understanding is the Kodiak brackets and crank pulley are different though. The GMT800 water crossover is the same as the GMT400/Van but the Kodiaks are different as are some RVs. The correct one places the thermostat outlet slightly outboard of the driverside head. If you can find a newer 8.1L like 2005+ snag the timing cover, cam sensor amd timing set as well. The early cam sensors are discontinued and not serviced by anyone. Save yourself the headache and update to the newer parts. The newer one use a Gen III LS sensor and I doubt those will go away for a while. Before you stab the engine, hose down the crank sensor with penetrating oil where it goes into the block, remove the crank sensor and lube it really well with antisieze before re-installing it. They rust into place and can be impossible to remove without removing the transmission.

My 8.1Ls are all GM minus the headers. One has the 454HO/Base 502 cam and the other has the 8.1L HO Mag cam. I used the stock air box and intake tube on my Tahoe, then switched it out to a custom 4" tube with a cartridge style LS7 MAF. 8.1L with either of the cams I am running, long tubes and a tune is a ~450 hp engine with 550 tq. That 450 hp comes in at a nice ~5,000 rpm and torque peak around 3,000-3,500. The 454HO/502 cam makes a bit more grunt down low than the 8.1 HO cam but the HO cam is smoother running and the torque curve is a bit flatter through the midrange with its wider LSA. Then there is the aound difference between the firing orders. I am more of a 1-8-4-3-6-5-7-2 kind of guy.

Just for clarification, possibly bringing up more questions. The truck I’m looking to pull parts off isn’t a Kodiak, I believe the technical model, according to gm websites, is a 01-02 C3500HD Cab and Chassis “classic”, it’s a true GMT400 platform with the 8.1 from factory, only other engine option being the 6.5TD. However, if these 01-02 vans/kodiaks/rvs/busses are similar enough to the GMT400 platform, they are MUCH more common around me, and I’d happily pull parts off of those. The front accessory brackets I would still like to pull off of the cab and chassis, because it still sat low in the engine back and theoretically should easily clear both my frame and hood. But if all I just said you already knew, than my next question/clarification is about the cooling and fuel system, so my factory 454 cooling system (radiator, main hose locations etc) should work correct? What about fuel system? Would I need to update/upgrade pump? Or lines? I’ll probably be using the factory 8.1 exhaust manifolds, mainly because I’m concerned of fitment between gmt800 headers and gmt400 engine bay, then build the rest of the exhaust from there. I’ve found that stock 454 engine mounts should work with the 8.1, which means my theory about the accessory brackets should be correct. Also I’ve already picked up my donor engine, it’s a 2006 8.1, from a 3500 pickup, ran great but was my buddies truck he wrecked. So if I read correctly, the 8.1’s had two cams from factory? How would I go about finding that out? So I can get the correct tune for the 0411 PCM. And I’ll likely create my own intake tube, that shouldn’t be much of an issue, finding placement for the sensor may be a concern though. Any input or clarification is greatly appreciated, and thanks for everything so far.

 

[L31MaxExpress]

00CrewCab, the factory horsepower ratings wouldn't explain the dramatic differences
in performance that you have observed. Possibly the disparity is because the factory
ratings are based on healthy examples? Check this out:

* '96-'00 L29 7.4L (454) = 290HP / 410 ft-lbs torque

* '01-'03 L18 8.1L (496) = 340HP / 455 ft-lbs torque
* '04-'06 L18 8.1L (496) = 320HP / 420 ft-lbs torque

(Source: dieselhub.com article LINK)

Who knows? You may have been unfortunate enough to have driven not 1 but 2
wounded warriors? My '99 C2500 is no lightweight, but it pulls hard on the onramp,
and effortlessly continues towards triple digits. In English, the drivetrain seems to
have much more headroom than my wallet does. :0)

FWIW I've also driven a 305ci/5-spd GMT400, and it was a night & day difference.
The 305 felt like I was always driving uphill, whereas the 454 feels like I'm always
driving downhill. The difference is not subtle.

Don't get me wrong, I'm not try to call you out at all. Given the numbers above, if you
were used to a happy 454 punching out it's rated 410 ft-lbs of torque, and then managed
to swap in a '04 8.1 putting out it's rated 420 ft-lbs of torque, I don't think the difference
(stock) would be all that much to write home about. Sure, it would be great engine bay
eye candy at the local show & shine, but the 'back dyno' (ie: how far you get pushed into
the seat at WOT) might be in for a disappointment. (Especially if you were to also use
the Allison? Possibly moving from the 4L80-E to Allison accounts for the net loss in HP
& torque between the '01-'03 vs '04-'06 offerings? The Allison is made for long lasting
with severe service, and my understanding is that is takes more HP to run the
transmission itself?)

****

If it helps any to understand where I'm coming from, I started messing with BBCs ever since
a buddy bought a worn out 6 year old '73 Camper Special with a 454/Turbo 400/4:11 and
we rebuilt it to pull harder than new: (Misspent Youth)

To summarize, I'm not trying to talk you out of this at all. Actually, if the 8.1L engine was
the proverbial flagpole on a freezing day, I'd be the one to triple dog dare you to see if your
tongue would get stuck to it. :0)

Seriously, if you go for the 8.1 make sure to pick & choose carefully so that you will have no
fear of an old mild-mannered white-haired dude showing up in dark blue truck and keeping up
with you...or at the very least making it a 'too close for comfort' race at the local drag strip.

Do your homework & make me afraid to drive in Kansas. This would make for a terrific build
thread for all to enjoy & learn from!

I have driven and owned both in stock form. The L18 8.1L makes the L29 454 look like it is in reverse when the hammer is all the way down on the 8.1L. The 8.1 torque curve is flatter, longer and there is more of it. The 8.1 has 50 hp on the 454 Vortec. The Allison trucks feel down on power compared to the 4L80E/4L85E ones until about 10,000 lbs goes behind it. Unloaded an 8.1L Van, Avalanche or Suburban will run out extremely well especially with the 4.10 gear option. I drove an 8.1/4L80E/3.42 geared long wheelbase passenger van a few times. It had more get up and go than the 7.4/4L80E/4.10 Suburban I drove about the same time period. The 2005 Suburban I looked at was the 340 hp and 455 tq version. It had 120K on it and plenty of get up and go. The 8.1Ls gain like 40-50 hp and 50-60 ft/lbs of torque tuning them as well without touching anything. The 8.1 has a 60 second delay at WOT before it goes into power enrichment mode.

 

[Road Trip]

PS: @00CrewCab , if you follow @L31MaxExpress 's guidance you will definitely end up with something
that would make me afraid of driving the chore truck in the Sunflower state. Whatever
he recommends he can back up based upon real world testing.

Matter of fact I'm glad that we aren't neighbors, for I would no doubt get sucked into
a friendly engine bay arms race of sorts...with the risk of having to learn his driving patterns
& avoid driving during those times. His engine mojo is strong.