L18 8.1L swap resource thread

[Larry]

I skimmed and didn't see this covered, thought I would share.

When doing an 8.1 swap and you plug off the oil cooler ports, the oil is then rerouted to the oil cooler bypass valve. I would remove the filter adapter and pull this valve as it is no longer needed. On our most recent 8.1 swap this valve was stuck, which gave zero oil pressure. You can also see the ports in the bypass are not very large. Another thing to keep in mind is the filter bypass no longer works with the cooler ports plugged.

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I agree, that is a good item to add for those of us not using external oil coolers. Just this past weekend someone was asking me what Allen head was the correct size to remove the oil filter adapter in order to get it out of the way to pluck out the bypass valve. Do you recall what size Allen head it was?

Thanks for the added info!

 

[Team208Motorsports]

Do you recall what size Allen head it was?

1/2" i believe.

 

[shady]

248,000 miles too much for a running donor on an 8.1?


Edit: it's $2500 for the whole truck

 

[Larry]

248,000 miles too much for a running donor on an 8.1?


Edit: it's $2500 for the whole truck

That is a lot of miles, but I think I mentioned my company sold 1,242 2007 Model Year Workhorse chassis to UPS with 8.1L’s. Many of those now have well over 200K and 300K and still going strong.

$2500 would be way too much for the engine but for the whole truck that isn’t too bad although I would try to do a little better on the price. For reference, a buddy and I scored this one last year for $1000 albeit it was 2wd with a 6.0L. We made a ton of money parting this thing out. This one had 368K on it. The 6.0L had a plugged up PCV and was blowing oil out of the dip stick. Planned on using the engine for a 4x4 Van project but my buddy abandon that project and sold the engine/4L80E (he has a difficult time staying focused on pretty much anything). The profit from this truck would have more than paid for the 6.0L swap and most of the van build costs. Ah, well. It was his build, not mine

Wasn’t much left when we were done. Between selling every bit and piece I bet we quadrupled our money.

It was a shame to throw away such a clean body but you can’t keep everything

 

[shady]

Yeah I've been thinking that's a lot of miles... Wife was kinda pissy when I said I might buy it lol. That 6.0 truck you bought was a $5-6k truck around here all day. Wouldn't have even had to wait to sell it probably lol. If I found a 6.0/4l80e truck around here for $1000 I'd buy it that day..... Cheapest I've found is $3500 with 250,000 miles. That's why I was excited about that 8.1 when I seen it. Cheapest 8.1 truck I found before that one had 200+ and was all rusted n dented for $5000.

 

[Blue85]

Is there a good resource documenting swapping between 5.3/6.0 and 8.1L engines? It seems for GMT800-series swapping between would be much easier than into a square body, but I haven't seen the basic questions answered on any of the GM truck forums. Examples:

• Can the 8.1L run on a 6.0L PCM via a calibration change or does the crank sensor require either a) wiring change or b) PCM swap.
• Can the whole 8.1L harness and PCM plug into a 2500 with 4L80-E?
• 8.1's were available without the body lift, so the radiator must be shorter than the Duramax rad, but is it the same as the 6.0 rad?
• What's required between BCM and PCM to sync up the VIN?
• Does 8.1 flexplate work with 6.0 torque converter?

Likewise, there may be guys with 5.3/6.0 in their square body interested in swapping to 8.1, which should be much easier than going from old SBC/BBC.

 

[Larry]

Is there a good resource documenting swapping between 5.3/6.0 and 8.1L engines? It seems for GMT800-series swapping between would be much easier than into a square body, but I haven't seen the basic questions answered on any of the GM truck forums. Examples:

• Can the 8.1L run on a 6.0L PCM via a calibration change or does the crank sensor require either a) wiring change or b) PCM swap.
• Can the whole 8.1L harness and PCM plug into a 2500 with 4L80-E?
• 8.1's were available without the body lift, so the radiator must be shorter than the Duramax rad, but is it the same as the 6.0 rad?
• What's required between BCM and PCM to sync up the VIN?
• Does 8.1 flexplate work with 6.0 torque converter?

Likewise, there may be guys with 5.3/6.0 in their square body interested in swapping to 8.1, which should be much easier than going from old SBC/BBC.

I can’t answer that but I can tell you there is a Facebook group called “8.1 8100 496 Vortec Info Swap Classifieds” that have many guys that have swapped 8.1’s into everything from 1940’s cars to Dodge Ram Chargers to late model Suburban’s and everything in between. Especially, the group Admin, Ed Coss, could answer many of your questions has he has swapped 8.1s into GMT400s and 800’s but I’ll take a stab at your questions as well.

• Can the 8.1L run on a 6.0L PCM via a calibration change or does the crank sensor require either a) wiring change or b) PCM swap.
  Yes, the 8.1L ECM is not specific to just the 8.1L. Same 12200411 ECM used in the same generation 4.8 on up to 6.0 engines. The calibrations are obviously different though. Yes, the wires inside the CAM and Crank sensor connectors must be swapped. Not swap cam for crank but the wires inside those sensor connectors need to be swapped.
• Can the whole 8.1L harness and PCM plug into a 2500 with 4L80-E?
  Yes, for the most part… I would venture to say yes with some minor rework but if a vehicle already has a period correct 4.8 up on to 6.0 the original harness could easily be reworked by the cam/crank repin and possibly extending a few leads. In all reality, the Howell 8.1L harness is nothing more than a same generation LS harness but with longer leads and cam/crank repin. Again, Ed Coss on that FB page could confirm.
• 8.1's were available without the body lift, so the radiator must be shorter than the Duramax rad, but is it the same as the 6.0 rad?
  Good question for the FB group or go do some research on Spectra Premium’s website to see what they show for part number usage across the different engines. Comparing part numbers on various part supplier websites is the best way to confirm what is compatible and what isn’t. I can tell you the radiator in my stock 2001 Silvy HD with an 8.1L sits pretty low below the top of the radiator support.
• What's required between BCM and PCM to sync up the VIN? Good question for a tuner
• Does 8.1 flexplate work with 6.0 torque converter?
  Dunno for certain as mine are manuals but I would venture to say most likely. It is possible the 8.1/Allison flexpate may be different than an 8.1/4L80E as in G-vans, Subs, and Avalanches. Research the part numbers on Napa, A/C Delco or whose ever website to check usages.

 

[bigblock72]

I can’t answer that but I can tell you there is a Facebook group called “8.1 8100 496 Vortec Info Swap Classifieds” that have many guys that have swapped 8.1’s into everything from 1940’s cars to Dodge Ram Chargers to late model Suburban’s and everything in between. Especially, the group Admin, Ed Coss, could answer many of your questions has he has swapped 8.1s into GMT400s and 800’s but I’ll take a stab at your questions as well.

I'll add my .0005 cents worth.

• Can the 8.1L run on a 6.0L PCM via a calibration change or does the crank sensor require either a) wiring change or b) PCM swap.
  Yes, the 8.1L ECM is not specific to just the 8.1L. Same 12200411 ECM used in the same generation 4.8 on up to 6.0 engines. The calibrations are obviously different though. Yes, the wires inside the CAM and Crank sensor connectors must be swapped. Not swap cam for crank but the wires inside those sensor connectors need to be swapped.
• Can the whole 8.1L harness and PCM plug into a 2500 with 4L80-E?
  Yes, for the most part… I would venture to say yes with some minor rework but if a vehicle already has a period correct 4.8 up on to 6.0 the original harness could easily be reworked by the cam/crank repin and possibly extending a few leads. In all reality, the Howell 8.1L harness is nothing more than a same generation LS harness but with longer leads and cam/crank repin. Again, Ed Coss on that FB page could confirm.
• 8.1's were available without the body lift, so the radiator must be shorter than the Duramax rad, but is it the same as the 6.0 rad?
  Good question for the FB group or go do some research on Spectra Premium’s website to see what they show for part number usage across the different engines. Comparing part numbers on various part supplier websites is the best way to confirm what is compatible and what isn’t. I can tell you the radiator in my stock 2001 Silvy HD with an 8.1L sits pretty low below the top of the radiator support. The 3/4 ton suburbans have a taller radiator support than the 1/2 tons. The 6.0l radiator is about 4 inches shorter and uses a spacer between the radiator and the support. You will want the taller 8.1l fan and shroud. I think the 8.1 uses larger diameter oil cooler lines that won't be compatible with the 6.0 radiator, not 100% on that though. If you deleted the oil cooler lines a 6.0 radiator may be sufficient for a 8.1 depending on application and use.
• What's required between BCM and PCM to sync up the VIN? Good question for a tuner Easiest to flash the same VIN in both modules using GM software, can get a little tricky depending on what features you want to use.
• Does 8.1 flexplate work with 6.0 torque converter?
  Dunno for certain as mine are manuals but I would venture to say most likely. It is possible the 8.1/Allison flexpate may be different than an 8.1/4L80E as in G-vans, Subs, and Avalanches. Research the part numbers on Napa, A/C Delco or whose ever website to check usages. The 8.1 flexplate is just your standard 91-up big block piece with a 11.5" 6 bolt pattern that should be compatible with most if not all 4l80/85 converters.

 

[RootBreaker]

so I have been so tired of tuning my carb'd motor. so want to do a 8.1L...
I am seeing mention of an 8.8L out there now... so maybe go 8.1L to get truck all setup for it then 8.8 some day??? mmmmm

is there a better 8.1L out of all the years to really look for? my 78 chevy would love a nice new heart and I'm so considering it when I get my bonus in March (wife will be pissed but what else is new)...

When I am ready... I know a guy who sells vehicles that were in accidents and really banged up. maybe I can find something with an 8.1L Tboned or something. I know a guy that bought a truck from him with a 6.0L for $2200 and got to hear it run. Was rear ended then rolled....

 

[Kay86K5]

so I have been so tired of tuning my carb'd motor. so want to do a 8.1L...
I am seeing mention of an 8.8L out there now... so maybe go 8.1L to get truck all setup for it then 8.8 some day??? mmmmm

is there a better 8.1L out of all the years to really look for? my 78 chevy would love a nice new heart and I'm so considering it when I get my bonus in March (wife will be pissed but what else is new)...

When I am ready... I know a guy who sells vehicles that were in accidents and really banged up. maybe I can find something with an 8.1L Tboned or something. I know a guy that bought a truck from him with a 6.0L for $2200 and got to hear it run. Was rear ended then rolled....

Larry spells everything out really good in this thread. Its a long thread, but worth reading the whole thing to really learn the ins and outs of the 8.1 and also swapping into a square. But in short, pretty much all the years of the 8.1's are relatively the same as far as "which year is best". Some came with different bracket assemblies on the front (referred to as workhorse or van assemblies) but if you really don't care about keeping or having AC in your truck, then getting a normal 8.1 out of a 3/4 or 1 ton truck is fine. Earlier years (up to 2003) had a return style fuel rail on it, which can make it a lot easier to deal with your fuel setup in a square body (just get a TBI tank with an EP381 pump, then run two high pressure lines from the tank and hook up to motor). 2004 and up used a returnless fuel rail (there is info out there of how to still make this work in a swap, but just a little more of an annoyance IMO). Also 2004 and up they got rid of the stupid EGR tube off the back of the motor. It's nice to not have that. If you get a 2001-2003 motor, and you don't have to do emissions, then you can just get the block off plates and remove EGR from the tune and your good.

Other than that, really doesn't matter which year you get, I'd say just look for one with the lowest miles for the best price, but seen lots of dudes go way into the 200K+ miles on these motors with no real issues...its a good motor

 

[RootBreaker]

yeah I was reading it and so much info, I was bleeding knowledge outta my ears!!!! hah.. I was on google and forget where but someone said depending on which year/truck you could get 325hp all the way up to 450hp .. stock... that is why I asked as I didn't see that mentioned. maybe ill have to search up and find that to quote it. I do need new fuel tanks (1 removed already and other super rusted) so maybe ill go tbi tank anyway and run that pump as I have an electric fuel pump now and put a regulator on the line to just use it for now. hmmmm

 

[wheels87k5]

@Larry,
Did you use the same radiator for both the '78 and '89 with the 8.1? I just read the whole thread and never seen anything on what radiator you used. I remember reading that you got a couple delivered and they were damaged but I didn't see anything on what you ended up with.
I'm doing a 7.4 Vortec swap and wanted to use the same one that came with the donor truck. But it's huge compared to the one that's in my 87 Blazer with the 350 TBI. Did you have to use a different radiator support or just modify the one with the smaller radiator? If there is a link for this, let me know and I'll do my research there.

 

[Larry]

@Larry,
Did you use the same radiator for both the '78 and '89 with the 8.1? I just read the whole thread and never seen anything on what radiator you used. I remember reading that you got a couple delivered and they were damaged but I didn't see anything on what you ended up with.
I'm doing a 7.4 Vortec swap and wanted to use the same one that came with the donor truck. But it's huge compared to the one that's in my 87 Blazer with the 350 TBI. Did you have to use a different radiator support or just modify the one with the smaller radiator? If there is a link for this, let me know and I'll do my research there.

No sir. The radiator in the 78 K10 is a 73-80 flat nose specific big radiator. I don’t have the part number but it was the largest radiator for a 73-80 truck. The Suburban has a Spectra Premium CU774

 

[wheels87k5]

That's kind of what I thought on the Suburban as far as using the CU774. I now recall reading that somewhere but just can't place it at the moment. That just means I'll need to modify my radiator support to make one fit properly. Which also means getting A/C hoses made. No big deal. Just wanted to make sure on fitment.

Amazing what can be done with a welder and some wire.

Thanks for the input.

 

[Kay86K5]

I used a radiator from a mid 80's suburban with a 6.2 diesel (radiator and shroud). Used the same brackets that attach to the core support as what my TBI350 radiator was using, and just bolted it in. It's much larger than a 350 radiator, but is meant to fit in a square body. Just an FYI really

I purchased the radiator and shroud together off ebay for a good price

 

[RootBreaker]

hmmm I have a 1986 4 core radiator from a 454... that should also be stock and usable?

 

[Kay86K5]

hmmm I have a 1986 4 core radiator from a 454... that should also be stock and usable?

I would think so. What's nice about the square bodies core support is it has the "mounting" threaded wholes for both the small block radiators, or the big block/6.2 larger radiators. So you should be able to just pull out your small block radiator, drop in the larger one, and then use the exact same mounting brackets, just bolted into the other holes....at least that's what I did, worked just fine

 

[Kay86K5]

I then just went to the local parts store and purchased some "universal" radiator hoses that can be shaped and molded how you want, and hooked up the upper and lower hoses as I needed...that was easy peasy

 

[RootBreaker]

I would think so. What's nice about the square bodies core support is it has the "mounting" threaded wholes for both the small block radiators, or the big block/6.2 larger radiators. So you should be able to just pull out your small block radiator, drop in the larger one, and then use the exact same mounting brackets, just bolted into the other holes....at least that's what I did, worked just fine

hmm not sure what the 350 bolt holes vs big block were but like said.. I bought an entire front clip off of a BB truck.. and it looks like this. only thing I have handy at the moment..

 

[Larry]

I used a radiator from a mid 80's suburban with a 6.2 diesel (radiator and shroud). Used the same brackets that attach to the core support as what my TBI350 radiator was using, and just bolted it in. It's much larger than a 350 radiator, but is meant to fit in a square body. Just an FYI really

I purchased the radiator and shroud together off ebay for a good price

Yep, exactly what I did. It’s all pretty well documented in my Polar Bear thread. The 8.1L swap starts on page 16 with the radiator details further down.

The whole big diesel radiator has been talked about in many threads here over the past few months. Regarding an 8.1L swap, I honestly can’t remember what I used for an upper hose on my Polar Bear Suburban, but my spreadsheet says a Gates 20416 for a Silverado 8.1L application. I swore I changed it again a while after the 8.1L swap with a better fitting hose by just walking the isle at Napa to find one formed with the right bends then cut it to fit but that could have been the K10. I get the two confused. The lower hose is just a period correct BBC hose where I list I used a Napa 70752 for a 1990 R2500 Suburban 7.4L for the lower hose position.

This is what a CU774 (81-91 Diesel radiator) radiator and shrouds look like. I have seen this in every 6.2L diesel truck I’ve ever laid eyes on including little 2wd half tons with diesels. In fact, my shroud, brackets and upper radiator cover came from a mid-80’s 2wd half-ton 6.2L diesel. I have also seen this big honking radiator in big block chassis cabs and a few crew cabs but not all big block squares came with this big radiator. The radiator is not equally proportioned as it is positioned further to the driver’s side than passenger’s side. The passenger’s side uses the same bracket holes as smaller radiators while the driver’s side uses the set that is closer to the fender.

Zoomad also just had some pictures up in a radiator thread last week with comparo pictures of the big diesel radiator (CU774) pieces vs. the typical small block radiator and bits. You can see how the shroud is offset.