6.6 Gas L8T Engine Swap in 2015 Suburban

[L8T BURB]

Hello all! My 2015 Suburban is currently dead. 186k miles with a collapsed lifter and a VERY tired transmission. Current plan was to refresh the engine with non-AFM parts, and go back with a GM reman 6l80 transmission. However, I am recently seeing a lot of information about the L8T engine, which is the 6.6 liter gas engine that GM is using in its HD truck applications.

I have read that this engine has no AFM/DOD/DFM systems on it, and is tuned to run on 87 octane with HP around 400, and TQ around 440. Research also shows that this engine bolts directly to a 6L80 transmission.

When looking at dollars vs dollars, I would be nearly the same money to swap a sub 10k miles 6.6 gas engine w/6L80 in my Suburban as opposed to freshening up my 186k mile 5.3 and going with a reman GM 6L80.

Does anyone here have any insight on this or otherwise informed opinions? I am leaning heavily towards going this route, unless there is just some massive deal breaker with compatibility of the 6.6 in my Suburban.

Thanks in advance!

 

[strutaeng]

No, but it sounds cool as heck!

There's some guys that have used the factory 6.6 gas engine crankshaft straight from parts dealerships (it's a forged crank) into their 6.0 blocks to make like a stroker from GM factory parts.

I guess the only downfall is that it's direct injected. But the aftermarket guys have figured out how to swap the intake for a port injection. That's probably more for like a swap vehicle that didn't have direct injection.

 

[L8T BURB]

No, but it sounds cool as heck!

There's some guys that have used the factory 6.6 gas engine crankshaft straight from parts dealerships (it's a forged crank) into their 6.0 blocks to make like a stroker from GM factory parts.

I guess the only downfall is that it's direct injected. But the aftermarket guys have figured out how to swap the intake for a port injection. That's probably more for like a swap vehicle that didn't have direct injection.

My research suggests that both the 5.3 L83 and the 6.6 L8T are both direct injected. So maybe that part won't be an issue?

 

[Marky Dissod]

Are you trying to swap in the 6.6L direct injected V8 for a 5.3L direct injected V8?

If so, you should get in touch with a pcm tuner.
It's not quite as simple as we'd all be hoping, but any tuner competent with segment swapping should be able to make this doable.

 

[L8T BURB]

Are you trying to swap in the 6.6L direct injected V8 for a 5.3L direct injected V8?

If so, you should get in touch with a pcm tuner.
It's not quite as simple as we'd all be hoping, but any tuner competent with segment swapping should be able to make this doable.

This is correct. I am eyeing a full engine/transmission dropout from a 2021 Silverado 2500 to put in my 2015 Suburban. I found that HP Tuners has in fact cracked the ECM of those engines, which gives me more faith that this may be an attainable swap.

I am awaiting the green light from my technician. If he says yes, I will be purchasing the engine and transmission this weekend.

 

[Marky Dissod]

If your technician is not HPTuners-literate, be prepared to seek out another tuner.

 

[CMoore711]

I have read that this engine has no AFM/DOD/DFM systems on it, and is tuned to run on

When looking at dollars vs dollars, I would be nearly the same money to swap a sub 10k miles 6.6 gas engine w/6L80 in my Suburban as opposed to freshening up my 186k mile 5.3 and going with a reman GM 6L80.

I don’t have any specific technical knowledge to contribute here.

But I really like where this thread is going!

And for these 2 reasons above that I quoted from the OP are strong logical reasons that support why you should pull the trigger and make it happen.

I would maybe look into what model PCM and TCM the 6.6 L8T runs on? Compare that to the PCM & TCM in your 2015 Suburban.

Questions:
Can you run your current PCM/TCM with the 6.6 L8T and just have it tuned appropriately?

If yes; Then on the surface I’d say you should be good to go.

Would you have to swap your PCM and TCM to a different model for the 6.6 L8T than what’s in your ‘15 Suburban now?

If yes; Then the swap may prove to be more difficult than it sounds.

 

[L8T BURB]

If your technician is not HPTuners-literate, be prepared to seek out another tuner.

I've lucked up on this technician. He is the one who turned me on to HP tuners, so I'm hoping it'll be smooth.

A couple things I'm seeing that I had not previously accounted for...

The L8T engine uses a hydraulic power steering system rather than electronic on the Suburban. Would it be easy to ditch it for electronic, or better to convert my Suburban to hydraulic?

Also I noticed the L8T has a mechanical cooling fan that's driven by belt rather than the electronic cooling fan on my Suburban. Any idea if this would be an issue?

The engine/trans I'm looking at comes with all accessory drive components as well as ECM. It's as complete as an engine swap could be.

 

[CMoore711]

The fan shouldn’t be too big of a deal. That should be able to be converted to electric fans with GM OEM parts and a relay pretty easily. You should get with your technician/tuner on doing so.

In fact if your electric fans on your 5.3 pull enough CFM to accomodate cooling the 6.6 maybe your technician/tuner could whip up a harness and relay to reuse your current electric fan set up for the swap?

 

[L8T BURB]

I am also interfacing with someone on the HP tuners forum who has successfully done this swap on a Sierra Denali 1500. This was his response...

It will be an awesome swap. My daily is a 2016 Sierra Denali with a 6.6L swap. If you can get the complete engine, that would be the way to go. In your case, you can use your original ECM and wiring harness. You'll just have to swap your original 4 pin fuel rail sensor instead of the 3 pin sensor on the L8T.
The vacuum pump will have to be deleted as well, since the L8T doesn't have mounting provisions. That's an easy job as well.

Thoughts?

Thanks all!

Michael

 

[Marky Dissod]

The L8T engine uses a hydraulic power steering system rather than electronic on the Suburban.
Would it be easy to ditch it for electronic, or better to convert my Suburban to hydraulic?

I would not be surprised if the aluminum blocks lack the ability to hang power steering onto them, whereas only the iron block L8T would have such bosses to mount power steering.
Long story short, prepare to go hydraulic, unless you are willing to swim uphill for 2 or 3MpG.

Also I noticed the L8T has a mech cooling fan, belt-driven, rather than the electronic cooling fan on my Suburban.
Any idea if this would be an issue?

If the L8T & your 5.3L engine both use very similar or identical pcms, you'll wind up with the ability to choose between electronic fans with pcm control, or mech fan.If you tow HEAVY, mech fan. If not, electronic fans.

The engine/trans I'm looking at comes with all accessory drive components as well as ECM.
It's as complete as an engine swap could be.

And I bet dollars t' donuts the transmission attached to the L8T comes with its own tcm too.
USE THOSE!
To be clear: lean very heavily toward using the L8T's engine AND transmission control moduleS if at all possible.

Save your 5.3L ecm & tcm.
If they are BOTH sufficiently similar to the L8T's ecm & tcm, keep and use them for custom tuning purposes.

Sell your 5.3L engine -unless you want to keep it (for future upgrades?).
Keep your 5.3L's transmission to use as a core, or upgrade-rebuild it.

 

[B-train]

This is an AWESOME thread! I'm super excited to see how it works out. You may have opened pandoras box to making these SUVS bullet proof and long lasting w/o the CAFE BS that plagues them with age.

Thanks for taking the leap for us!

 

[CMoore711]

I am also interfacing with someone on the HP tuners forum who has successfully done this swap on a Sierra Denali 1500. This was his response...

It will be an awesome swap. My daily is a 2016 Sierra Denali with a 6.6L swap. If you can get the complete engine, that would be the way to go. In your case, you can use your original ECM and wiring harness. You'll just have to swap your original 4 pin fuel rail sensor instead of the 3 pin sensor on the L8T.
The vacuum pump will have to be deleted as well, since the L8T doesn't have mounting provisions. That's an easy job as well.

Thoughts?

Thanks all!

Michael

Boom goes the dynamite.

Between this guys experience and your technician/tuner telling you it’s doable I’d say order the L8T motor and transmission and do it.

 

[L8T BURB]

The next point of contention here looks to be whether the 6L90 transmission could be made to fit my Suburban? The donor L8T comes with a 6L90 attached to it. Both my Suburban and the donor are 2WD. Of course my Suburban has the 6L80.

Any insight on what would need to be done? Perhaps shorten the driveshaft?

I am currently negotiating with the seller on the L8T donor. Will update once I secure it!

 

[Geotrash]

The next point of contention here looks to be whether the 6L90 transmission could be made to fit my Suburban? The donor L8T comes with a 6L90 attached to it. Both my Suburban and the donor are 2WD. Of course my Suburban has the 6L80.

Any insight on what would need to be done? Perhaps shorten the driveshaft?

I am currently negotiating with the seller on the L8T donor. Will update once I secure it!

The 6L90 is longer but I believe the mounts are in the same place so all you should probably need to worry about are having a shorter driveshaft fabricated and perhaps adapting the u-joints.

 

[strutaeng]

So sounds like the typical GM LS/LT swap, i.e., "plug and play!" LOL

 

[Marky Dissod]

The variances between the 6L80E & 6L90E can likely be handled by a different driveshaft, a rubber mallet, and patience.
Can you make use of the 6L90E driveshaft that already came with it? Or do you need a different other one?

 

[L8T BURB]

The variances between the 6L80E & 6L90E can likely be handled by a different driveshaft, a rubber mallet, and patience.
Can you make use of the 6L90E driveshaft that already came with it? Or do you need a different other one?

The donor vehicle with the L8T is not available for me to get the driveshaft from. I talked to my technician today and he suggested that (if needed) we could utilize a driveline shop that's the next town over and have them cut down the driveshaft. Feeling pretty good about this! In the final negotiating stage, all signs lead to me finalizing this deal tomorrow morning and freight to the shop by midweek next week!

 

[L8T BURB]

UPDATE!!

Engine/transmission has been purchased! The seller will be palletizing and prepping for shipment by weekend, and I should receive it by the middle of next week! I'm freaking PUMPED!!

Here are some pics of the donor vehicle and engine/transmission...

 

[L8T BURB]

Some more pics...