L86 to L8T in '19 Yukon XL Denali

[L8T BURB]

@L8T BURB, did you upgrade the axle gear, or did you keep 3.08?
Your metro/urban city MpG likely would have been improved by 3.42.

I kept the stock gearing in place. Getting a 10 speed behind that engine would have been amazing too. I am curious to hear more about the driving experience of OP.

 

[Marky Dissod]

@L8T BURB, did you upgrade the axle gear, or did you keep 3.08?
Your metro/urban city MpG likely would have been improved by 3.42.

I kept the stock gearing in place. Getting a 10speed behind that engine would have been amazing too.

Getting a 10L90 behind an L8T, even with 3.08, would've been eye opening, mouth watering, and at times sphincter puckering - but always tragically cool.

 

[L8T BURB]

@chevman88 What grade of fuel are you running in the L8T? It is designed to run 87, and that is what I ran in mine, but I am curious what your stance is on the matter.

 

[Bigburb3500]

Getting a 10L90 behind an L8T, even with 3.08, would've been eye opening, mouth watering, and at times sphincter puckering - but always tragically cool.

If my 6L90 decides to give up… I’ve been messaging with PowertrainSwap about the 10L90 being able to be used. “In theory” it should all work. I am highly curious about OPs driving experience too!

 

[Geotrash]

If my 6L90 decides to give up… I’ve been messaging with PowertrainSwap about the 10L90 being able to be used. “In theory” it should all work. I am highly curious about OPs driving experience too!

I'm with you 100%, but per a few posts up, it seems the bell housing pattern is slightly different on the LT motors vs the LS's that you and I have in our 3500's. I don't believe the 10-speed was ever mated to an LS from the factory.

 

[Bigburb3500]

I'm with you 100%, but per a few posts up, it seems the bell housing pattern is slightly different on the LT motors vs the LS's that you and I have in our 3500's. I don't believe the 10-speed was ever mated to an LS from the factory.

Just because it didn’t come from the factory doesn’t mean it can’t be done! Don’t rain on the parade. The truck really needs 1 more OD gear for non-towing duties on the highway. Would bring up my MPG avg 1-2.

 

[Geotrash]

Just because it didn’t come from the factory doesn’t mean it can’t be done! Don’t rain on the parade. The truck really needs 1 more OD gear for non-towing duties on the highway. Would bring up my MPG avg 1-2.

I agree it would make a great package if it’s possible! I’m also a fan of the venerable 6.0. It’s likely to outlive me!

 

[Marky Dissod]

The truck really needs 1 more OD gear for non-towing duties on the highway. Would bring up my MpG avg 1-2.

6L80's 4th: 1.152 . . . 6L80's 5th: 0.852 . . . 6L80's 6th: 0.667 . . . 6L80's biggest mistake: lacks a direct drive.
Blame Ravigneaux & LePelletier?
8L90's 6th: 1.000 . . . 8L90's 7th: 0.845 . . . 8L90's 8th: 0.652
10L80 7th: 1.000 . . . 10L80 8th: 0.854 . . . 10L80 9th: 0.689 . . . 10L80 10th: 0.636
However, unless you have a lil plug-in to disable Engine Confusion, see 10L80 9th.

 

[Bigburb3500]

6L80's 4th: 1.152 . . . 6L80's 5th: 0.852 . . . 6L80's 6th: 0.667 . . . 6L80's biggest mistake: lacks a direct drive. Blame Ravigneaux & LePelletier?
8L90's 6th: 1.000 . . . 8L90's 7th: 0.845 . . . 8L90's 8th: 0.652
10L80 7th: 1.000 . . . 10L80 8th: 0.854 . . . 10L80 9th: 0.689 . . . 10L80 10th: 0.636
However, unless you have a lil plug-in to disable Engine Confusion, see 10L80 9th.

If I am reading this correctly, the final ratios in the 8 and 10 speed would bring down the RPMs cruising down the highway. With 4.10s at 70-75mph I’m at 2200-2400RPM (iirc). The truck gets much better MPG when below 2k RPM - as in 1-3MPG better based on digital display.

 

[Marky Dissod]

If I read this correctly, the final ratios in the
6L80, or 8L90, or 10L80
would bring down the RpMs cruising down the highway.
With 4.10 at 70-75MpH I’m at 2200-2400RPM (iirc).
The truck gets much better MpG when below 2k RPM - as in 1-3MPG better based on digital display.

The next-to-final and final gears of the 6L80 & 8L90 are pretty damn close to the same,
and 8th and 9th of the 10L80 are pretty damn close to the same too.
If you can take advantage of 10th (can keep the TCC locked) and downshift to 9th as rarely as possible,
yes, it can be worth a few MpG.

However, if you cruise at a high enough road speed, the 10L80 MIGHT vacillate between 9th & 10th?
Which I guess would still be better than just 9th?

Oh, by the way:
more to come ...