Engine swap

emtnm · August 8, 2022

I know I might get some flack for this but here it goes. I am thinking about taking out my 8.1 and swapping it for a 5.3. Just wondering if the wiring, or computers need to be changed. I’m mainly considering doing this because of fuel mileage and needing to find an oil leak that might be causing the engine to knock really bad. Any info that can be provided would be greatly appreciated.

shakenfake · August 8, 2022

You do not want a 5.3 in a 2500 truck.

You would have to change the wiring. I believe that the 8.1 computer will work with a 5.3 but I cannot remember

emtnm · August 8, 2022

Why would going to the 5.3 be a bad idea? What about going to the 6.0?

Edited August 8, 2022 by emtnm

David89GMC · August 9, 2022

Why would an oil leak cause the engine to knock?

You won't like the 5.3 if you ever try to tow anything.

Just how can you justify the expense? How many YEARS of ga$ $aving$ will the 5.3 $$$wap have over just keeping the 8.1? That's an expensive swap.

If you're able to swap the 8.1 for a 5.3 and handle the technical issues, why can't you just coax more fuel mileage from the 8.1?

A smaller engine will have to work harder than a large engine, so the 5.3 mileage won't be nearly what you expect.

Get a good programmer and adjust the parameters until your 8.1 mileage gets better.

emtnm · August 9, 2022

What programmer would you recommend?

davester · August 9, 2022

Just to follow up with your original idea, you need the engine, transmission, transfer case, wiring harnesses at least for the engine, transmission, and to the bcm (unless you like diffing the wiring diagram and repinning/wiring stuff, ecm at least, custom fab a driveshaft, possibly the front one as well, instrument panel (it's programmed different between gas and diesel), if the two trucks have different option packages, that is more work to either transplant or get it going.

And that's it you transplant in the 6.0/4l80e

Edit:

Oh yeah, I believe the radiator, shrouds and metal piece (forget the name of it) that goes across the front of the truck holding the radiator are all different as well.

Edited August 9, 2022 by davester

shakenfake · August 9, 2022

6.0 would be a great idea. I would do that. Skip the programmer though, you are not going to get any real mileage out of it.

@davester This is a gasser to gasser swap not a diesel to gasser swap. Half that stuff you just brought up does not need to be touched at all lol

davester · August 9, 2022

ok, you don't need to do the engine harness, bcm, ip. Still need to change all the driveline parts, and rewiring the transmission harness.

emtnm · August 9, 2022

51 minutes ago, davester said:

ok, you don't need to do the engine harness, bcm, ip. Still need to change all the driveline parts, and rewiring the transmission harness.

Are you talking all driveline part, ie: differentials and rear axle?

shakenfake · August 9, 2022

You would only need to do that if it came with an Allison.

Also I don't think the original engine harness works with an LS. The 8.1 is not an LS and therefore has different connectors.

davester · August 10, 2022

The 8.1 comes with an Allison. You don't need to replace the front/rear diff, but the driveshaft will be a different length and you probably would need some adapter u-joints.

emtnm · August 10, 2022

Will the 6.0 work with the Allison transmission?

davester · August 10, 2022

From brief googling, it should bolt up to the allison, so that would cut down a lot of work. You'd have to sort out flexplate/starter/engine mounts and then clearance around the front of the engine (as the engine is a little shorter, you still want the fan in the shroud to pull air through the radiators). And you may want to regear it as the 6.0 will be happier with 4.10's vs I think the 8.1 normally gets 3.73.

emtnm · August 10, 2022

Thank you all for your help. I will be coming back and asking more questions as the time for the swap comes near (if the wife actually lets me).

shakenfake · August 12, 2022

On 8/9/2022 at 9:39 PM, davester said:

The 8.1 comes with an Allison. You don't need to replace the front/rear diff, but the driveshaft will be a different length and you probably would need some adapter u-joints.

Not all 8.1s came with an Allison. The did come with a 4L80 as well.

The Allison has it's own TCM, trying to tie that into the PCM may be tricky