The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post

pilotXC · 11-04-2019, 01:58 AM

I'm in the process and beginning stages of doing an LQ4/4L80E swap into my 1972 K20. I bought the truck about 3.5 years ago and thought it was in good shape when I got it. Has a GM crate engine, 350, from 1994 with a TH350 behind it and NP205 transfer case. Seemed to run strong and well in general. I had to fix some wiring issues, replace the steering box, tie rod ends, get an alignment, new seat cover and fix some rust under the rear window seal from a very leaky sliding rear window within the first few months of buying it. I had a couple years of trouble free driving overall then went to replace the master cylinder and had a hell of a time getting the lines bled, had to replace the proportioning valve that turned out to be faulty, then had to do it all again... Noticed a radiator leak at the same time so pulled the radiator and it was shot, so had it rebuilt and realized that the cooling system was a lot worse than I thought it was. Ran tons of water through it to try to clean it out, finally thought it was good and put it all back together... A few months ago out of no where I got a very loud "ping" start and took me a while to figure out what was going on. Finally found out I had no compression in #3 and #5, air was passing between the two cylinders. I pulled the head and the gasket was blown. Thought that's all it was, then a buddy noticed a hairline crack between the cylinder walls that was very difficult to spot. That immediately threw everything into a tail spin. Obviously I could find a new 350 block and swap everything over, which wouldn't be terrible, but the more I started reading and talking to the same friend (he has done a couple 5.3L swaps into Jeep's) I decided if I was pulling the engine, I'd much rather have a modern power plant. Started looking for a donor and found the combo I have now. It's been such a puzzle to try to find info for what I'm doing and there are obviously different ways to go about the swap, but wanted to try to consolidate all my learnings into one place in hopes it might help someone else on their project, so here goes...

Transmission:
This is the biggest issue I've run into. Trying to marry the 4L80E with my NP205. I found 2 viable options that I was planning to choose from originally:

1. Advance Adapters - They make what looks like a great package of the adapter that will bolt to the trans side 6 bolt pattern and an input shaft to swap in the transfer case. You also have to have the housing machined to accept the 90mm bearing for the larger 32 spline input shaft. If you have a 4wd 4L80E you also have the output shaft swapped to a 2wd shaft and have the rear relucter ring installed if your donor trans is 1997 or later. You're probably looking at minimum $1000 just to get the existing 27 spline NP205 to work. That doesn't include the speedometer sensor in the tail housing of the transfer case either.
https://www.advanceadapters.com/prod...h350-or-sm465/

2. Offroad Designs - I did some calling around and when I looked at what they had online and talked to them, this was the route I was planning to go. They offer a similar kit that AA does, but they build it to work with a 4wd 4L80E so you DO NOT have to swap the trans output shaft. You would also need to machine the input housing for the 90mm bearing. They also offer a service to machine the NP205 tail housing to accept the donor VSS for $195, plus shipping both ways. Pretty sweet package and they were super cool and told me, if you find a TH400 adapter for an NP205 and can get it machined down 1/16 you will accomplish exactly what we offer for that portion. Still would have to do the input shaft, but still, very cool of a company to tell you exactly what they do so you can do it yourself if you are capable.
http://offroaddesign.com/catalog/Tra...seAdapters.htm
http://offroaddesign.com/catalog/NP205VSS.htm

Ok, so I was pretty convinced that was my plan, but then my friend said, doesn't a NP241 or an NP208 bolt right onto a 4L80E? Good question. I called Offroad Designs back the next morning and asked, they said, yes, will bolt right up. Change of plans. I started looking around for one of these instead. I'm not building anything crazy, just a driver so these would be totally fine options. I found a NP208 locally for a good deal with linkage, shifter, and even a slip yoke driveline, so I grabbed that to throw in... Problem hopefully solved.

Next is the speedo. How to get a mechanical gauge work with VSS tech. The guy doing my harness told me about Dakota Digital pass through pulse generators and said I can program your PCM on the rear speed sensor for the 8 pulse output from the pulse generator so your speedo will work and transmission will shift correctly. He said he's used it a few times and seems to work great and it's $42 on Summit. That problem solved too, hopefully.
https://www.summitracing.com/parts/dak-sen-01-4160

For motor mounts, I went with Dirty Dingo's cross member and motor mount combo. I haven't pulled it out of the box yet, but looks pretty cool and I love the ability to access the pan if needed. The stock cross member won't come out without some serious negotiating with the engine mounts at best I learned... How often will I need to drop the pan? Hopefully rarely if ever, but I like having the option. I read you can modify the stock cross member and haven't seen a lot builds where people call out this being an issue, but when I called Dirty Dingo, they said the engine will not fit unless you do this cross member change...
https://www.dirtydingo.com/shop/prod...oducts_id=1408

So far, I'm putting new gaskets and seals on the engine, having the transmission given a once over just to make sure it's going to be good once it's in. Figured I'd rather do it now when it's out and easy to get to it than wait and see what happens, even though the place I got if said it's fine and it shifted smooth. Just want the piece of mind... As I started doing the gaskets, I got trapped in the rabbit hole that's so easy to go down. I got a water pump and oil pump and knew I wanted to do those, but once I got it a part I decided since it's a part and the cover is off, I should do the timing chain and power steering pump. Also heard to replace the oil galley barbell when I do the rear main seal and rear cover gasket. I didn't want to or plan to do all of this, but it's one of those things that once you start looking at things and thinking about it, you might as well do it since you have it a part and the engine is out. Again, I would prefer to have the piece of mind to know these things are new not having the repair history on the engine.

My truck has 3 tanks currently as well, stock behind the seat and the dealer option saddle tanks. I wanted to get rid of the behind the seat tank anyway to free up the space and not listen to gas slosh around anymore, and found out I can do a 6 port selector valve and 2 in tank pumps wired up to a switch in the cab. Then decided, with some pushing from my buddy, maybe I won't need 2 tanks and I can add the selector valve and switch later if I want and save myself one more headache to try to get done with the swap.

Still trying to figure out things like if I want to pay for electric fans now or just go with mechanical to get it going and make that switch later? What to do for trans cooler lines to the stock radiator, radiator hoses, if I should or need to swap the battery from the passenger side to the driver side, etc.
No pictures to share really at this point, nothing much has been done yet, just been trying to line everything up. The next few weeks should ramp up and I'll try to post some follow up on how everything works out. Hope some of this is helpful to have it consolidated in one post.

11-04-2019, 01:58 AM	#1
pilotXC Registered User Join Date: Feb 2016 Location: Portland OR Posts: 154	1972 K20 LQ4/4L80E Swap I'm in the process and beginning stages of doing an LQ4/4L80E swap into my 1972 K20. I bought the truck about 3.5 years ago and thought it was in good shape when I got it. Has a GM crate engine, 350, from 1994 with a TH350 behind it and NP205 transfer case. Seemed to run strong and well in general. I had to fix some wiring issues, replace the steering box, tie rod ends, get an alignment, new seat cover and fix some rust under the rear window seal from a very leaky sliding rear window within the first few months of buying it. I had a couple years of trouble free driving overall then went to replace the master cylinder and had a hell of a time getting the lines bled, had to replace the proportioning valve that turned out to be faulty, then had to do it all again... Noticed a radiator leak at the same time so pulled the radiator and it was shot, so had it rebuilt and realized that the cooling system was a lot worse than I thought it was. Ran tons of water through it to try to clean it out, finally thought it was good and put it all back together... A few months ago out of no where I got a very loud "ping" start and took me a while to figure out what was going on. Finally found out I had no compression in #3 and #5, air was passing between the two cylinders. I pulled the head and the gasket was blown. Thought that's all it was, then a buddy noticed a hairline crack between the cylinder walls that was very difficult to spot. That immediately threw everything into a tail spin. Obviously I could find a new 350 block and swap everything over, which wouldn't be terrible, but the more I started reading and talking to the same friend (he has done a couple 5.3L swaps into Jeep's) I decided if I was pulling the engine, I'd much rather have a modern power plant. Started looking for a donor and found the combo I have now. It's been such a puzzle to try to find info for what I'm doing and there are obviously different ways to go about the swap, but wanted to try to consolidate all my learnings into one place in hopes it might help someone else on their project, so here goes... Transmission: This is the biggest issue I've run into. Trying to marry the 4L80E with my NP205. I found 2 viable options that I was planning to choose from originally: 1. Advance Adapters - They make what looks like a great package of the adapter that will bolt to the trans side 6 bolt pattern and an input shaft to swap in the transfer case. You also have to have the housing machined to accept the 90mm bearing for the larger 32 spline input shaft. If you have a 4wd 4L80E you also have the output shaft swapped to a 2wd shaft and have the rear relucter ring installed if your donor trans is 1997 or later. You're probably looking at minimum $1000 just to get the existing 27 spline NP205 to work. That doesn't include the speedometer sensor in the tail housing of the transfer case either. https://www.advanceadapters.com/prod...h350-or-sm465/ 2. Offroad Designs - I did some calling around and when I looked at what they had online and talked to them, this was the route I was planning to go. They offer a similar kit that AA does, but they build it to work with a 4wd 4L80E so you DO NOT have to swap the trans output shaft. You would also need to machine the input housing for the 90mm bearing. They also offer a service to machine the NP205 tail housing to accept the donor VSS for $195, plus shipping both ways. Pretty sweet package and they were super cool and told me, if you find a TH400 adapter for an NP205 and can get it machined down 1/16 you will accomplish exactly what we offer for that portion. Still would have to do the input shaft, but still, very cool of a company to tell you exactly what they do so you can do it yourself if you are capable. http://offroaddesign.com/catalog/Tra...seAdapters.htm http://offroaddesign.com/catalog/NP205VSS.htm Ok, so I was pretty convinced that was my plan, but then my friend said, doesn't a NP241 or an NP208 bolt right onto a 4L80E? Good question. I called Offroad Designs back the next morning and asked, they said, yes, will bolt right up. Change of plans. I started looking around for one of these instead. I'm not building anything crazy, just a driver so these would be totally fine options. I found a NP208 locally for a good deal with linkage, shifter, and even a slip yoke driveline, so I grabbed that to throw in... Problem hopefully solved. Next is the speedo. How to get a mechanical gauge work with VSS tech. The guy doing my harness told me about Dakota Digital pass through pulse generators and said I can program your PCM on the rear speed sensor for the 8 pulse output from the pulse generator so your speedo will work and transmission will shift correctly. He said he's used it a few times and seems to work great and it's $42 on Summit. That problem solved too, hopefully. https://www.summitracing.com/parts/dak-sen-01-4160 For motor mounts, I went with Dirty Dingo's cross member and motor mount combo. I haven't pulled it out of the box yet, but looks pretty cool and I love the ability to access the pan if needed. The stock cross member won't come out without some serious negotiating with the engine mounts at best I learned... How often will I need to drop the pan? Hopefully rarely if ever, but I like having the option. I read you can modify the stock cross member and haven't seen a lot builds where people call out this being an issue, but when I called Dirty Dingo, they said the engine will not fit unless you do this cross member change... https://www.dirtydingo.com/shop/prod...oducts_id=1408 So far, I'm putting new gaskets and seals on the engine, having the transmission given a once over just to make sure it's going to be good once it's in. Figured I'd rather do it now when it's out and easy to get to it than wait and see what happens, even though the place I got if said it's fine and it shifted smooth. Just want the piece of mind... As I started doing the gaskets, I got trapped in the rabbit hole that's so easy to go down. I got a water pump and oil pump and knew I wanted to do those, but once I got it a part I decided since it's a part and the cover is off, I should do the timing chain and power steering pump. Also heard to replace the oil galley barbell when I do the rear main seal and rear cover gasket. I didn't want to or plan to do all of this, but it's one of those things that once you start looking at things and thinking about it, you might as well do it since you have it a part and the engine is out. Again, I would prefer to have the piece of mind to know these things are new not having the repair history on the engine. My truck has 3 tanks currently as well, stock behind the seat and the dealer option saddle tanks. I wanted to get rid of the behind the seat tank anyway to free up the space and not listen to gas slosh around anymore, and found out I can do a 6 port selector valve and 2 in tank pumps wired up to a switch in the cab. Then decided, with some pushing from my buddy, maybe I won't need 2 tanks and I can add the selector valve and switch later if I want and save myself one more headache to try to get done with the swap. Still trying to figure out things like if I want to pay for electric fans now or just go with mechanical to get it going and make that switch later? What to do for trans cooler lines to the stock radiator, radiator hoses, if I should or need to swap the battery from the passenger side to the driver side, etc. No pictures to share really at this point, nothing much has been done yet, just been trying to line everything up. The next few weeks should ramp up and I'll try to post some follow up on how everything works out. Hope some of this is helpful to have it consolidated in one post.