6.6 Gas L8T Engine Swap in 2015 Suburban

[L8T BURB]

Every 4.8L, 5.3L. 5.7L, 6.0L, 6.2L, 6.6L, and 7.0L shares extremely similar external dimensions.
The whole point of a small-block.
If you don't already know for a fact that a jacqueswhole has swapped a 5.3L into a 'vette, just to get away with selling it to someone unawares ...
Now you know. If you can't believe it, DuckDuckGo it (googl me ars).
As for the 6L90, he did such a good job with that crossmember, the only people who will spot it are transmission and/or crossmember experts.
Never meant to be? They look right at home!

Speaking of 6.6L swaps, dig these DuraMax conversion firms:

Predator Duramax Suburban

predatorinc.com

Duramax Specialties, LLC

Thank you for your patience, this page is currently under development. Feel free to call or visit us at the links above.

duramaxsuv.com

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Precision Fabrication Plus Inc.

Specializing in '60-'91 GM Duramax Swaps and '01-'18 GM IFS DELETE Conversion Systems. From mild to wild we do it all!

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Blame CAFE MpG standards for the fact that we can't go to a dealership and order powertrains like a Five Guys burger.

If you were to consider selling it, consider / research how well Suburban 2500s hold their value.
In other words, when you do sell it, you'd better have sold it for enough money to feel really good about it - because you'll STILL regret it.

Honestly I didn't realize the whole engine family was so similar. Maybe I should have went with the 7.0L 427! I've known about the Duramax swaps for quite some time. I guess I was basing my comment about it being unique off of the fact that it was an engine that just debuted a couple of years ago, and I hadn't seen such a swap done on any 2015-2020 Suburban at the time I did my swap.

Either way, you're right. It'd likely take more than anyone's willing to pay me in order for me to feel good about selling it.

 

[Marky Dissod]

Maybe I should have went with the 7.0L 427!

Although LS7s are awesome, I consider them out of character in bubbas. Plus they're a tease in a CAFE-world.
L8Ts are designed spec'd and built to work HARD for 300,000 miles.
How do you feel about the axle gear - 3.08, yeah? Normally, I'll rant
'Every GM truck and suv with a 6L80 should have either 3.42 or 3.73, damnt!'
whenever reasonably possible - but if I were you, I'd likely let it be in your case, you lucky bastaducci.

Congratulations on doing what GM should have done.

 

[blackelky]

If, and it is a BIG if....I was to consider selling this thing, any idea on what someone would be willing to pay? It being a highly specific, 1 off type of build, and the mileage, I'm concerned I'd get burned on any sort of good sale price. This thing is a MONSTER since the engine swap.

Highlights as follows...

2015 Suburban, 2WD, 189K miles.
Tan leather interior w/captains chairs
Factory overhead Blu-Ray player

Just 3k miles ago the following repairs were done...

Brand new 6.6 engine transmission (No DOD/AFM)
Brand new 6L90 transmission
New driveshaft
New ball joints, inner and outer tie Rods, new front shocks/struts, new rear shocks
New steering wheel (old one had peeling leather)
New motor mounts

Cosmetic stuff
22 inch RST wheels/tires from a 2022 Suburban w/3k miles
2022 Suburban RST wheels w/3k miles
5% tint on all windows w/5% strip on windshield

All said, engine and transmission cost was $7500, other miscellaneous parts another $1000, and total labor cost for all repairs was $6500. Crazy...I KNOW lol! It's basically a bulletproof Suburban at this point though.

View attachment 420224View attachment 420225View attachment 420226

Idk.. but take my money lol that things a beast. Hoovies garage or cleetus would probably buy it asap.

 

[CMoore711]

What would a stock comparable vehicle in similar condition go for? I'd go from there, and maybe add another 10k--or a little less. That's just off the top of my head.

I agree with this and would be my recommendation as well, that's probably a good starting point.

Unfortunately the majority of full-size GM SUV customers don't know the value of having a motor that doesn't have AFM/DOD and the value of the additional reliability that brings to the vehicle. Hell, most full-size GM SUV customers/owners don't even know how it works or what it does mechanically. Which is also why you're potential buying pool of finding someone willing to pay for the drivetrain upgrades you've done is super small.

If you were seriously considering selling it your best avenue would be GM SUV and truck forums, bring a trailer, cars & bids, and eBay. Your chances of exposure to potential enthusiast owners who would likely appreciate (and place value) on the upgrades you've done is going to be larger on those platforms versus autotrader, cargurus, etc.

However, that being said you said it:

Either way, you're right. It'd likely take more than anyone's willing to pay me in order for me to feel good about selling it.

This is so true. The reality it regardless it'll be listed for sale for a long time before the right buyer comes along and is willing to come close to a dollar amount you're willing to accept for it.

Because of these factors your best bet to ensure you're getting the most value out of the upgrades you've already done is to just drive it and enjoy it. You're already "pot committed" at this point. There's no reason why you shouldn't be able to put another 150K+ miles on that bad boy with routine maintenance.

I think it's a bad a$$ daily driver family hauler. The L8T and 6l90e swap you've done has like you said, pretty much made your Suburban bullet proof. You've done some nice clean subtle changes to the exterior with the "RST" theme; Black out that window trim and you're chrome delete is done.

The swap was just completed not long ago, I think you're still sorting out the exhaust or cat situation but that's a small piece of the equation money wise at this point.

The way I see it you have two things that would keep you from enjoying this rig for another 150K+ miles:
1. Rust
2. Keeping the paint looking good and in good condition

I'm not sure what all on the front end has new paint; If it's just the grill or if the front bumper recently got a re-spray as well. If it did I would put some PPF on the front bumper and grill ASAP to keep them protected and looking new for longer. Then have a under coating/rust proof treatment done to the underside, frame, inside doors, fenders, and tail gate.

Then just drive and enjoy...

 

[RobH]

This may have already been covered.

@L8T BURB's investment is his new 2021 transmission and V8. We all know that he has much more than a rebuilt 2015 V8 and 6L80E. But, that was his cost. So, selling it as a 2015 Suburban with new engine/transmission replacement in 2023 should get back his investment over the value of his 2015 Suburban with worn out engine and transmission. FWIW and YMMV.

 

[L8T BURB]

Anyone else got an old tired 5.3 or 6.2 and looking to upgrade? Peep this listing. 6.6 with 0 miles on it for UNDER 5k! Just swap over your accessories, tune and you're ready to go!! Idk if you can even get a reman 5.3 for this price!

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[TollKeeper]

I dont think it would fit in my Envoy.. And I still havent figured out what I would do about my front diff
(in case you didnt know, my front diff is mounted to the oil pan, and my oil pan has a pass through for the axle)

 

[Marky Dissod]

I dont think it would fit in my Envoy ... still haven't figured out what I would do about my front diff
(in case you didnt know, my front diff is mounted to the oil pan, and my oil pan has a pass through for the axle)

Has a direct dimensional comparison between Gen4-LS vs Gen5-LT 4WD or AWD been done yet?

But every 'small block V8' is pretty much the same size regardless of displacement.
In other words, there should be enough room under a GMT360's hood for an L8T.

 

[CMoore711]

I dont think it would fit in my Envoy.. And I still havent figured out what I would do about my front diff
(in case you didnt know, my front diff is mounted to the oil pan, and my oil pan has a pass through for the axle)

I owned an AWD TBSS for almost 10 years and 200K miles. I am unfortunately quite familiar with the ba$**** front diff oil pan design and front carrier housing…. I don’t miss it.

 

[NPKennny]

@L8T BURB

Excellent write-up and thread! Thank you. I have read it multiple times.

Can you verify that the 6.2L throttle body is the best fit for the 5.3 to 6.6 swap in a 2015? In hindsight, would you have opted for aftermarket motor mounts?

NPK

 

[Tremek]

Hey gents, great thread. I’m currently planning to do something similar to my (thankfully still running perfectly well) 2016 GMC Yukon XL Denali 4WD currently at 124k miles, but with more forced induction!

Being the Denali trim my truck currently has the 6.2L L86 with AFM & DOD, but I’m either hearing lifters at idle or an exhaust leak, so it’s likely getting to be the time to dig into this thing before something mechanically unfortunate happens that leaves me stranded somewhere.

I’m also going to stay with the 8L90e; while I can appreciate the 6L90e (I had a 2012 CTS-V wagon for years) I prefer the driving dynamics of the 8 speed versus the 6.

There’s a few reasons I’m going to go likely with a supercharger; I live at elevation and despite naturally aspirated motors being inherently less complex, there’s no replacement for displacement AND boost!

My goals are a reliable ~700hp at the crank and that being transmitted reliably through the 8L90e (need some input on who builds ‘built’/stage-whatever 8 speeds?) as well as through the transfer cases and diffs. I like the Denali’s ability to either go into 4H/L or function as AWD, so I have no illusions as to the necessity of both dropping the L8T + boost agent in it as well as refreshing the rest of the driveline including reinforced driveshafts as I gather none of these trucks’ OEM drivelines appreciate either turning 75% more torque than factory or rotational speeds that come from a quarter mile.

Speaking of, not intending to do actual drag racing with the truck, but I want at my altitude something like high 12s and 110mph.

Anyway - anyone have any input on these new power adders intended for the L8T? Tempted to go with the 3.0L Whipple. I do tow on occasion and my goal is for the beast to be resilient enough to take any duty cycle I throw at it.

Here’s a pic of the truck as it sits. I put the 6-pot front Brembo RPO kit on it when I got it last year, the TE37 wheels, and a lowering kit to drop it a couple inches. Rides great (Magneride/magnetorheological shocks are my favorite thing GM does next to LS motors) and drives great.

 

[Tonyrodz]

Hey gents, great thread. I’m currently planning to do something similar to my (thankfully still running perfectly well) 2016 GMC Yukon XL Denali 4WD currently at 124k miles, but with more forced induction!

Being the Denali trim my truck currently has the 6.2L L86 with AFM & DOD, but I’m either hearing lifters at idle or an exhaust leak, so it’s likely getting to be the time to dig into this thing before something mechanically unfortunate happens that leaves me stranded somewhere.

I’m also going to stay with the 8L90e; while I can appreciate the 6L90e (I had a 2012 CTS-V wagon for years) I prefer the driving dynamics of the 8 speed versus the 6.

There’s a few reasons I’m going to go likely with a supercharger; I live at elevation and despite naturally aspirated motors being inherently less complex, there’s no replacement for displacement AND boost!

My goals are a reliable ~700hp at the crank and that being transmitted reliably through the 8L90e (need some input on who builds ‘built’/stage-whatever 8 speeds?) as well as through the transfer cases and diffs. I like the Denali’s ability to either go into 4H/L or function as AWD, so I have no illusions as to the necessity of both dropping the L8T + boost agent in it as well as refreshing the rest of the driveline including reinforced driveshafts as I gather none of these trucks’ OEM drivelines appreciate either turning 75% more torque than factory or rotational speeds that come from a quarter mile.

Speaking of, not intending to do actual drag racing with the truck, but I want at my altitude something like high 12s and 110mph.

Anyway - anyone have any input on these new power adders intended for the L8T? Tempted to go with the 3.0L Whipple. I do tow on occasion and my goal is for the beast to be resilient enough to take any duty cycle I throw at it.

Here’s a pic of the truck as it sits. I put the 6-pot front Brembo RPO kit on it when I got it last year, the TE37 wheels, and a lowering kit to drop it a couple inches. Rides great (Magneride/magnetorheological shocks are my favorite thing GM does next to LS motors) and drives great.

I like your rims. They look like declads.

 

[buckwild27]

You can swap out the 8 speed for a 10 speed.

https://www.powertrainswapsolutions.com/2015-2020-gm-suv

 

[Tremek]

I like your rims. They look like declads.

Thanks! They’re RAYS/Volk Racing 20x9.5 +0 offset 6x139.7 TE37 Ultra Large forged wheels intended for Toyotas (same bolt pattern) but using hub-centric aluminum spacers to take the intended-for-Toyota 112mm center hub bore down to the 78.1mm hub these trucks have.

Using the hub centric spacers means I haven’t figured out a good way to affix the center caps yet but I’ll get there.

 

[Tremek]

You can swap out the 8 speed for a 10 speed.

https://www.powertrainswapsolutions.com/2015-2020-gm-suv

Oh wow, I didn’t know about this being an option! We have what, a good 5+ years now of the 10L90e being used in high-power applications like the ZL1?

… With that said I know Ford has had a bunch of issues with their 10 speeds, and I understand GM and Ford collaborated on the design… Anyone know how well (or not well) GM’s version is holding up in heavy duty use?

 

[CMoore711]

You can swap out the 8 speed for a 10 speed.

https://www.powertrainswapsolutions.com/2015-2020-gm-suv

That’s the first I’ve see of that…

Interesting option.

I wish they would post the
“Supplemental parts list for the small parts required to complete install will be provided with the install kits, and instructions.”

 

[Marky Dissod]

You can swap out the 8 speed for a 10 speed.
https://www.powertrainswapsolutions.com/2015-2020-gm-suv

What's wrong with the 6L90?
NOT the 6L80E, the 6L90E - I thought that they did reasonably well behind the LGH DuraMax?

 

[buckwild27]

That guy seems to be having good luck with them. If and when I do this 10 speed conversion I will have the transmission rebuilt and beefed up.

 

[Tremek]

What's wrong with the 6L90?
NOT the 6L80E, the 6L90E - I thought that they did reasonably well behind the LGH DuraMax?

Not that it’s bad, but the 6L90e is a bit coarse compared to either the 8L90e or 10L90e; gear ratios are far more spread apart by comparison gear-to-gear and the 6L90e shifts substantially slower than either the 8 or 10 too, and I believe the overall ratio is narrower on the 6.

 

[Marky Dissod]

Not that it’s bad, but the 6L90E is a bit coarse compared to either the 8L90E or 10L90E;
gear ratios are far more spread apart by comparison gear-to-gear
and the 6L90e shifts substantially slower than either the 8 or 10 too,
and I believe the overall ratio is narrower on the 6.

An awfully imprecise representation of what you just said:

10L80: ... 4.69 ... 2.99 ... 2.15 ... 1.77 ... 1.52 ... 1.28 ... 1.000 ... 0.85 ... 0.69 ... 0.64 (7.32 Spread)
8L90E: ... 4.56 ... 2.97 .... 2.08 .... 1.69 . . . . . . . 1.27 ... 1.000 ... 0.85 . . . . . . . 0.65 (7.01 SPread)
6L90E: . . . . 4.03 . . . . 2.36 . . . . . . . . . 1.53 . . . . 1.15 . . . . . . . 0.85 . . . . . 0.67 (6.01 Spread)
4L60E: . . . . . . . 3.06 . . . . . . . . . . 1.63 . . . . . . . . . . . . 1.000 . . . . . . . . 0.69 (4.43 Spread)

As important as highway MpG has always been, clearly improving city MpG was even more important.

But it doesn't seem like there's any more MpG to be found in the next transmission ...