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L18 8.1L swap resource thread

Hi All!
It looks like I will be doing the 8.1 swap on my 91 in the next month or so. I have been debating replacing the tired TBI for a few months now and was focused on an lq4/lq9. Our friends at PacFab have been walking me through the 8.1 world and I have read this post thoroughly. I have not decided if I should do the physical part of the swap on my own or not, might be impossible due to other requirements and I need it done by Easter break next year. I will be doing the 8.1/4l80e/np205 replacing TBI350/4l60/np241. My junk is about 7200lbs with all gear inside and I am now towing an excursion trailer so the BBC makes sense. I do worry about fuel though, hoping that I can keep my foot off the gas :)

My only question is around how PacFab does the harness or if the Howell setup would be the way to go....

Dave
 
I don't think you could go wrong with a harness from either but if you have friends at PacFac anxious to help you I'd go with them. I know I would be interested in trying someone other than Howell for the next project.

I ordered the harness and tune for my Suburban to be exactly the same as my K10. The second harness arrived totally different and needed a few hours of rework to move things where I wanted and there is no way the tune is the same as the trucks run quite a bit different. The K10 has more low end grunt and the Burb feels to have more higher revving gonads by my butt dyno. Both rigs are the exact same with transmissions, gears and tires except the Burb has shorty headers. It would be hard to beleive shortly headers alone would make such a difference. I actually prefer how the K10 runs with a stronger low end.

One piece of advise I would give you is to have the harness builder wire and tune in the EVAP purge solenoid. Mine smell pretty gassy on hot days. So badly wish I would have done more on the EVAP side to make it functional
 
I used Tilden Motorsports (sister company of Pac fab ran outta the same building from my understanding). Their harness was good. The didnt label anything like Howell does, but to be honest, a moron can hook up a pre-worked harness. All the plugs can really only plug into 1 port. But Howell or Tilden would be just fine. Both are good reputable companies
 
GWeakland620 said:
Did you cut the frame a bit on the K10 then?
Click to expand...

No way dude! You only have to do that when the 8.1 manifolds are used. I'm using typical old squarebody 454 manifolds. The 8.1 accepts any ole BBC manifold or header. There is no acceptable reason to cut the frame but people do it all the time for some dumbass reason
 
Thanks Larry,
So it looks like my 8.1 will come from a 2002 HD work truck with a 2WD 4L80E. It has the AC bracket high on driver side. I have not seen any issues specific to the 2002, speak up if I missed something

My K5 has the following specs:
5.13s/37" tires, D60 & 14 bolt FF, original TBI 350/4L60/NP241, SYE on 241 with High Angle Drivelines CV unit. Hydro boost brakes with PS system cooler. I also have an engine oil cooler (stock).

So I am looking at additional parts for the following (with Tilden):
* 2002 8.1L with AC
* Harness, include 4l80e, EGR block, remove torque management, other
* Replace cam and crank sensors
* Transmission - looking at rebuilt units, upgrade seems straight forward for the 'low' horsepower of the stock 8.1. What stall speed torque converter do y'all recommend?
* 4l80e crossmember / tranny mount
* Tilden Cold Air Intake
* Cross Member - will use ORD unit
* NP 205 - will use ORD rebuilt unit
* Radiator - C&R
* Tilden fuel system upgrade kit
* Exhaust manifold from older big block truck

Some minor questions stated above, just thought I would put this out here for discussion/sanity check.

Mine will be the 2nd one (with AC)

8.1.jpg
 
2Dogs said:
Thanks Larry,
So it looks like my 8.1 will come from a 2002 HD work truck with a 2WD 4L80E. It has the AC bracket high on driver side. I have not seen any issues specific to the 2002, speak up if I missed something

My K5 has the following specs:
5.13s/37" tires, D60 & 14 bolt FF, original TBI 350/4L60/NP241, SYE on 241 with High Angle Drivelines CV unit. Hydro boost brakes with PS system cooler. I also have an engine oil cooler (stock).

So I am looking at additional parts for the following (with Tilden):
* 2002 8.1L with AC
* Harness, include 4l80e, EGR block, remove torque management, other
* Replace cam and crank sensors
* Transmission - looking at rebuilt units, upgrade seems straight forward for the 'low' horsepower of the stock 8.1. What stall speed torque converter do y'all recommend?
* 4l80e crossmember / tranny mount
* Tilden Cold Air Intake
* Cross Member - will use ORD unit
* NP 205 - will use ORD rebuilt unit
* Radiator - C&R
* Tilden fuel system upgrade kit
* Exhaust manifold from older big block truck

Some minor questions stated above, just thought I would put this out here for discussion/sanity check.

Mine will be the 2nd one (with AC)

View attachment 314549
Click to expand...
I have heard of bad oil pump drives on the 02 and 03 engines, something to think about before the install.
 
2Dogs said:
Thanks Larry,
So it looks like my 8.1 will come from a 2002 HD work truck with a 2WD 4L80E. It has the AC bracket high on driver side. I have not seen any issues specific to the 2002, speak up if I missed something

My K5 has the following specs:
5.13s/37" tires, D60 & 14 bolt FF, original TBI 350/4L60/NP241, SYE on 241 with High Angle Drivelines CV unit. Hydro boost brakes with PS system cooler. I also have an engine oil cooler (stock).

So I am looking at additional parts for the following (with Tilden):
* 2002 8.1L with AC
* Harness, include 4l80e, EGR block, remove torque management, other
* Replace cam and crank sensors
* Transmission - looking at rebuilt units, upgrade seems straight forward for the 'low' horsepower of the stock 8.1. What stall speed torque converter do y'all recommend?
* 4l80e crossmember / tranny mount
* Tilden Cold Air Intake
* Cross Member - will use ORD unit
* NP 205 - will use ORD rebuilt unit
* Radiator - C&R
* Tilden fuel system upgrade kit
* Exhaust manifold from older big block truck

Some minor questions stated above, just thought I would put this out here for discussion/sanity check.

Mine will be the 2nd one (with AC)

View attachment 314549
Click to expand...
I'd skip the NP205 and stick with the 241.
 
I am having a hard time finding the coolant crossover pipe. Is this going to be impossible to find?
 
2Dogs said:
Thanks Larry,
So it looks like my 8.1 will come from a 2002 HD work truck with a 2WD 4L80E. It has the AC bracket high on driver side. I have not seen any issues specific to the 2002, speak up if I missed something

My K5 has the following specs:
5.13s/37" tires, D60 & 14 bolt FF, original TBI 350/4L60/NP241, SYE on 241 with High Angle Drivelines CV unit. Hydro boost brakes with PS system cooler. I also have an engine oil cooler (stock).

So I am looking at additional parts for the following (with Tilden):
* 2002 8.1L with AC
* Harness, include 4l80e, EGR block, remove torque management, other
* Replace cam and crank sensors
* Transmission - looking at rebuilt units, upgrade seems straight forward for the 'low' horsepower of the stock 8.1. What stall speed torque converter do y'all recommend?
* 4l80e crossmember / tranny mount
* Tilden Cold Air Intake
* Cross Member - will use ORD unit
* NP 205 - will use ORD rebuilt unit
* Radiator - C&R
* Tilden fuel system upgrade kit
* Exhaust manifold from older big block truck

Some minor questions stated above, just thought I would put this out here for discussion/sanity check.

Mine will be the 2nd one (with AC)
Click to expand...
Looks like a good score. Getting an engine out of a 2001 or 2002 G-van or 3500-HD chassis cab is the best score one could stumble across. If that second engine is yours, it looks like it has everything you need bracket wise so I’m not sure why you have “2002 8.1L with AC” listed under additional parts needed??? Looks like it even has a neat A/C hose manifold to build upon.

Rick Capito said:
I have heard of bad oil pump drives on the 02 and 03 engines, something to think about before the install.
Click to expand...
I doubt there would even be anymore of the questionable oil pump shafts still on the road as most broke within a few thousand miles. I had to dig deep in my old emails but the improved oil pump drive shaft entered 8.1 production on 5-15-03 with Engine Serial T305190001

Justin V said:
I'd skip the NP205 and stick with the 241.
Click to expand...
Exactly. Nothing wrong with a 241 as long as it is well protected. You’re only going to whack it on a rock once! :haha:
 
Larry said:
Definitely not easy. Got to dig deep for those
Click to expand...
I emailed 3 of our yards that still had these engines on inventory, so I’ll see if one of them pull it for me. If more than one does, I’m buying all I can.
 
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