Considering a 6.0L to 8.1L swap
 

I have a chance to get an 8.1L engine out of a 2003 Sierra 2500 for pretty cheap. I am thinking of throwing it in my vehicle, a 2004 Yukon XL 2500 with 6.0L and 4L80e tranny. The 8.1L was an engine option on my truck, so i think it'll fit well.

I have a few questions to help decide how much extra $$$ I will need:
-will i need to change out my rad? the 8.1 uses a larger rad I think, but I'm wondering if I can get away with my current one for a while.
-what about headers and connecting to my existing stock exhaust?
-will I need a new computer and wiring harness, or can I make my existing one work?
-are there other gotchas that i should look out for?

I was originally planning on just changing out my cam, but have since found that my current engine is going to need a lot more work than I expected.

I was thinking I could build up the 8.1 into a pretty good engine, swap it out, rebuild the 6.0 and then sell it.

Am i crazy?

In my opinion its not really worth the trouble. With just a few swapped parts (alot less trouble) and less money you can make the same or better power, and more than likely still have better milage.

**all dependent on what goals you have**

Mostly torque for towing. From what I keep reading, the 8.1 is pretty good at keeping around 10mpg while pulling a few thousand pounds, and i know I can't get that in my truck right now, I'm closer to 7-8mpg while pulling a 16" trailer.
It definitely won't be a racer and I won't be going FI.

What have you done to the vehicle so far?
Adding some bolt-on's and a tune may get you where you want to be.
I really don't think the 8.1 would be worth it.

your going to need a new transmission or bell housing atleast. the 4l80e has a LS bolt pattern. I think.

The 8.1, Duramax and 4.8/5.3/6.0 all use the same bellhousing pattern which will also fit older 305/350's as well.

The 8.1 will tow a heavy load much better than the 6.0. Instead of having the 6.0 on the boards, the 8.1 will torque along at lower rpms much better.

Your PCM should be able to be tuned to work. You can use your 6.0 harness although some things will need to be lengthened. The PCM needs teh same info no matter what engine is used.

peace
Hog

So far i have a BB tune and intake, otherwise she is stock. After a recent road trip she has an oil leak that I suspect is coming from the head gasket area, and she has an engine rattle under load at the higher rpms. I'm not sure, but i think it's a lifter going. It sounds kind of like pre-detonation but i've tried all the way up to 93 octane fuel and it doesn't make a difference.
Beyond that, I figure the price of the engine is not much more than I could sell the old one for.

The 8.1 will out tow even a built 6.0 any day of the week, no way around it. You could turbo or supercharge the 6.0, but then mileage goes out the window. It's not a direct swap. If you tow over 6-7k often then I would consider it, if not, the 8.1's DD mileage of 11-12 empty will outweigh the benefits. I use an 8.1 avalanche at work to tow up to 22k combined weight, and it does very very well.

I forgot to mention that the current engine has just under 200,000 KMs (Canada) on it.

Don't the 2500 SUVs with the 8.1 have a body lift? I remember seeing somewhere that the 8.1 is taller and needs a lift. But heck, if you're going to put a body lift in it, get one large enough to fit that allison and put it in with the 8.1 (should already be attached to the 8.1 in the truck). Then it'll be a towing monster. The ally has much better gearing, especially in 1st gear to get loads moving. Just a thought.

I would get all the parts off the truck that you can. Cooling system, wiring harness, etc. The allison and it's associated parts would just be gravy from a towing standpoint if you can swing the extra cash. You'll need a tune for the 8.1 anyway.