2023 L8T 10 Speed

Ray Pickle · October 4, 2022

On 10/3/2022 at 5:22 PM, Another JR said:

This was discussed in another thread to some extent. A person with apparent insider knowledge said it was an engine cooling related issue (not water cooling) and hinted it was emissions related, but they were apparently not at liberty to give details. My speculation that it is NO/NO2 related is just common sense based on emissions knowledge I have from my work. It is just speculation, though.

TFL does what they do for uniformity not a fan of some of their dialogue but understand why they do that. The truck will climb long grades at high altitide at high rpm without overheating trans or coolant I have done it many times. Are there emmissions issues that just affect G.M. engines but not Ford gassers in that narrow circumstance thus causing a tuning adjustment that disallows downshifts to the proper gear for that circumstance? Possible/Maybe ? its beyond my purview. But to say " they have trouble on long grades and will only do 2400 rpm". is nonsense. I questioned the validity of the reasons for poor tuning being told it was due to poor thermodynamics/heat dissipation of l8t in that other thread and got nowhere regarding specifics other than I probably couldn't understand the subject matter well enough to follow along.

Another JR · October 5, 2022

4 hours ago, Ray Pickle said:

TFL does what they do for uniformity not a fan of some of their dialogue but understand why they do that. The truck will climb long grades at high altitide at high rpm without overheating trans or coolant I have done it many times. Are there emmissions issues that just affect G.M. engines but not Ford gassers in that narrow circumstance thus causing a tuning adjustment that disallows downshifts to the proper gear for that circumstance? Possible/Maybe ? its beyond my purview. But to say " they have trouble on long grades and will only do 2400 rpm". is nonsense. I questioned the validity of the reasons for poor tuning being told it was due to poor thermodynamics/heat dissipation of l8t in that other thread and got nowhere regarding specifics other than I probably couldn't understand the subject matter well enough to follow along.

Yes, it seemed clear that the person in that thread felt they could not give specifics. As you say, the truck does not have excessive coolant or transmission temperatures under those conditions. However, the actual combustion conditions at high altitude on warm days (lowest air density conditions) when attempting to get maximum available horsepower out of the engine lead to high combustion and exhaust gas temperatures. This increases the formation of NO and NO2. It’s not a matter of dissipating or rejecting heat - it’s simply a combustion temperature issue. The same problem exists with jet engine combustion.

I’m guessing they run into a temperature limit they’ve set to limit the emissions, the computer reduces the actual throttle plate position to limit power and rpm (despite the pedal position being floored), and truck won’t downshift because you can’t give it enough actual throttle to trip the downshift. Or they just directly prevent the downshift to limit rpm and thereby limit mass air flow, power and temperature. Again, my speculation on what they are actually doing to prevent the downshift.

Why didn’t the Ford 7.3 do the same thing? Same load, but almost 10% more rated horsepower, yes. But more importantly, look at the two videos. When the Chevy was tested they were in shirtsleeves and no snow in sight, not even on the nearby 12k mountaintops. Hot day for 11k feet. When the Ford was tested, they were all bundled up and there was snow all along the highway. Huge difference in temperature and air density, which causes a big difference in horsepower.

The difference in air density altitude for that maybe 40F temperature difference was about 4000 feet if I’m reading my charts correctly, so the Chevy was working with a very large additional maybe 12% horsepower reduction (using the rough power loss formula used in aviation) simply due the higher density altitude (lower air density) from the temperature difference. So there was a roughly 20% horsepower difference between the Ford and Chevy on their test days, more than half of which was caused by the temperature difference.

Edited October 5, 2022 by Another JR
Typo

SWDoodle · October 5, 2022

14 hours ago, Kjduvall said:

I'm just curious what the difference in parastatic loss are between the two trannys and if the added gear ratios will definitevly make up for it. As in heavy flywheel/heavy converter and more power loss to turn it, in relation to out put. I'm sure the 10spd is sweat. If it takes 40 more HP to turn it and a less snappy Rev range. will the (leverage of gears) be enough to over come that loss. Just some thinking I've been doing. Any thoughts???

That’s what I was curious about as well. From my memory the reason they never put the Allison 1000 behind the 6.0 was of the parasitic loss, hence why it was only offered with the 8.1 in the gas platform. Interesting enough with the L8T they did increase GCWR up to 26K for 2024 so I would assume there was no loss in performance.

I was gonna wait for a 2024 but ended up finding a 2023 Sierra SLE near me with the gas. I’ve had one heckuva time finding a pickup so I bit the bullet. My thoughts were to wait an see when this 2024 hits the road and get some real world reviews and then I can always trade up later. May be a year before we see many on the road anyway. Dealership I got this from had 2023’s on the lot and was still getting 2022’s in for customers!

Ray Pickle · October 5, 2022

12 hours ago, Another JR said:

Yes, it seemed clear that the person in that thread felt they could not give specifics. As you say, the truck does not have excessive coolant or transmission temperatures under those conditions. However, the actual combustion conditions at high altitude on warm days (lowest air density conditions) when attempting to get maximum available horsepower out of the engine lead to high combustion and exhaust gas temperatures. This increases the formation of NO and NO2. It’s not a matter of dissipating or rejecting heat - it’s simply a combustion temperature issue. The same problem exists with jet engine combustion.

I’m guessing they run into a temperature limit they’ve set to limit the emissions, the computer reduces the actual throttle plate position to limit power and rpm (despite the pedal position being floored), and truck won’t downshift because you can’t give it enough actual throttle to trip the downshift. Or they just directly prevent the downshift to limit rpm and thereby limit mass air flow, power and temperature. Again, my speculation on what they are actually doing to prevent the downshift.

Why didn’t the Ford 7.3 do the same thing? Same load, but almost 10% more rated horsepower, yes. But more importantly, look at the two videos. When the Chevy was tested they were in shirtsleeves and no snow in sight, not even on the nearby 12k mountaintops. Hot day for 11k feet. When the Ford was tested, they were all bundled up and there was snow all along the highway. Huge difference in temperature and air density, which causes a big difference in horsepower.

The difference in air density altitude for that maybe 40F temperature difference was about 4000 feet if I’m reading my charts correctly, so the Chevy was working with a very large additional maybe 12% horsepower reduction (using the rough power loss formula used in aviation) simply due the higher density altitude (lower air density) from the temperature difference. So there was a roughly 20% horsepower difference between the Ford and Chevy on their test days, more than half of which was caused by the temperature difference.

Agree with everything you said, my general message though is, the powertrain is being artificially limited. The why is speculation until otherwise proven. What you posit may well be true it just hasn't officially been explained. My truck WILL pull at or near redline up that exact pass if I choose to beat it that hard. I do think gearing between existing 2nd 3rd and 4th gear would improve tiwing experience under thise extreme conditions. That being said if the engine is outside its emmissions envelope and won't exceed 2400 to 2500 rpm when stressed, the transmission won't matter either way. The engine is operating under peak torque and significantly under peak h.p. It seems to me that combustion temps and trans temps would both be negatively impacted in that artificially created, "low rpm high demand scenario.

C/K Man · October 5, 2022

GM actually did put the Allison 1000/2000 behind the L96 6.0L, but only for Isuzu and Freightliner. I don't think the Allison would have made a difference in the HD pickups, it's still a 6 speed like the 6L90.

GMC4Zee · October 26, 2022

Glad we finally got the 10 speed. It will help with towing as sometimes it would seem just kicking to a slightly lower gear could keep the speed without a huge downshift and RPM rush when hitting hilly terrain. I would think because of the beefier trans they could eliminate some of the torque management and make it feel more peppy. I would like to see a bump in power to 440hp and 500lb/ft of torque in the next year or two. that would be a real nice gasser.

SWDoodle · October 27, 2022

Haven’t towed with my 23 yet, honestly really haven’t driven it much at all since I still kept my LML but I kind of anxious to see how it does with a little weight behind it. I got to a admit this thing is pretty peppy down low compared to my old 6.0 4 speed I used to have. But it kind of falls flat above 45 or so if you punch it, but it’s ok I guess. That’s where the 10 speed should make a difference. If they added 50/50 to it in hp/tq and still got decent mileage they would sell a lot of them, but I think the 10 speed will be an significant improvement.

Weighed my 23 last night and it was right at 7140 lbs empty for a CCSB 4x4 SLE. That’s 700 lbs lighter than my LML which weights about 7860. The gas platform definitely seems a little more nimble on the front end and it will be nice to have a little extra payload.

Epsilon Plus · November 15, 2022

On 10/5/2022 at 5:36 AM, SWDoodle said:

That’s what I was curious about as well. From my memory the reason they never put the Allison 1000 behind the 6.0 was of the parasitic loss, hence why it was only offered with the 8.1 in the gas platform. Interesting enough with the L8T they did increase GCWR up to 26K for 2024 so I would assume there was no loss in performance.

Fleets. Everyone forgets about the majority buyer of the gas HD platform. Fleet longevity has driven the gas HD decisions for many moons. The City of "x" is interested in longevity and commonality, not 400 gears to pull non-existent hills with.

We can thank fleet longevity for the lack of cylinder deactivation and stop start on the 6.6 as well as the IMO wise decision to keep the bulletproof 6L90 around.

All y'all TFL watchers that think your trucks will pull better in 7th at 2,400rpm than in 4th at 4,400rpm is why GM finally caved and gave you the more expensive and complicated 10. Enjoy your slightly better city MPG and same towing experience.

I can assure you that Freeport McMoRan , the Town of "x" and Granite Construction give 2 craps about the 10 speed and were fine with the 6L90 that was cheap and went 250k with the rest of their truck.

Pryme · November 16, 2022

2 hours ago, Epsilon Plus said:

Fleets. Everyone forgets about the majority buyer of the gas HD platform. Fleet longevity has driven the gas HD decisions for many moons. The City of "x" is interested in longevity and commonality, not 400 gears to pull non-existent hills with.

We can thank fleet longevity for the lack of cylinder deactivation and stop start on the 6.6 as well as the IMO wise decision to keep the bulletproof 6L90 around.

All y'all TFL watchers that think your trucks will pull better in 7th at 2,400rpm than in 4th at 4,400rpm is why GM finally caved and gave you the more expensive and complicated 10. Enjoy your slightly better city MPG and same towing experience.

I can assure you that Freeport McMoRan , the Town of "x" and Granite Construction give 2 craps about the 10 speed and were fine with the 6L90 that was cheap and went 250k with the rest of their truck.

Well said. Maybe I’m old school or just easy to please but I am more than content with the 6L90. I actually don’t like to feel a bunch of shifts as I’m driving up and down the road etc.

Another JR · November 16, 2022

56 minutes ago, Pryme said:

Well said. Maybe I’m old school or just easy to please but I am more than content with the 6L90. I actually don’t like to feel a bunch of shifts as I’m driving up and down the road etc.

Me three. I wanted reliability on the road and longevity over everything else.

Pryme · November 16, 2022

16 minutes ago, Another JR said:

Me three. I wanted reliability on the road and longevity over everything else.

Hopefully the direct injection and variable oil pump will prove to be reliable long term. Anyone run a catch can? I’ve seen a company that makes it but don’t know if it’s necessary

NaturallyAspirated · November 16, 2022

7 hours ago, Epsilon Plus said:

Fleets. Everyone forgets about the majority buyer of the gas HD platform. Fleet longevity has driven the gas HD decisions for many moons. The City of "x" is interested in longevity and commonality, not 400 gears to pull non-existent hills with.

We can thank fleet longevity for the lack of cylinder deactivation and stop start on the 6.6 as well as the IMO wise decision to keep the bulletproof 6L90 around.

All y'all TFL watchers that think your trucks will pull better in 7th at 2,400rpm than in 4th at 4,400rpm is why GM finally caved and gave you the more expensive and complicated 10. Enjoy your slightly better city MPG and same towing experience.

I can assure you that Freeport McMoRan , the Town of "x" and Granite Construction give 2 craps about the 10 speed and were fine with the 6L90 that was cheap and went 250k with the rest of their truck.

Agree 110%.
The real world.

SWDoodle · November 17, 2022

On 11/15/2022 at 5:17 PM, Epsilon Plus said:

Fleets. Everyone forgets about the majority buyer of the gas HD platform. Fleet longevity has driven the gas HD decisions for many moons. The City of "x" is interested in longevity and commonality, not 400 gears to pull non-existent hills with.

We can thank fleet longevity for the lack of cylinder deactivation and stop start on the 6.6 as well as the IMO wise decision to keep the bulletproof 6L90 around.

All y'all TFL watchers that think your trucks will pull better in 7th at 2,400rpm than in 4th at 4,400rpm is why GM finally caved and gave you the more expensive and complicated 10. Enjoy your slightly better city MPG and same towing experience.

I can assure you that Freeport McMoRan , the Town of "x" and Granite Construction give 2 craps about the 10 speed and were fine with the 6L90 that was cheap and went 250k with the rest of their truck.

I finally got a chance to tow some with the new 2023. Load was about 23K GCVW. So just about the max rating. It was pretty windy out so it was a pretty tough test. Overall I was pleased with the performance and for the most part it was holding 5th gear but would jump down to 4th once in a while. I live where it's flat so that makes a difference. It's definately better than my old 2005 6.0 gas would do with that load. I tried my best not to compare between my 2015 LML but it's hard not to think of the power the diesel has. My LML would have pulled in 5/6 with no issues. But the 6.6 has isn't a slouch either. I did some thinking on the 10 speed. I do think it will help getting loads up to speed. To me it seems like the 6L90E does great up to about 35 mph but really falls flat from 35-55ish IMO. Maybe a few more gears would help that area of the power band. I don't think it will make much difference once you get up to 65 mph as it's not gonna pull top gear anyway. Gas mileage was horrid, but I knew it would be, but don't have many miles on so hopefully it improves some. My area Diesel is $1.50 higher so it's wash anyway. I still wish they would come out with like a 7.0L type engine with 450hp/500+tq but sure that will never happen. With the new L5P hp/tq numbers that's gonna be a huge gap between the two platforms. Be interesting to see how the new 2024 performs with the 10 speed but honestly I don't think it's gonna be night and day between the 6L90E and that has been a pretty solid transmission. I never saw the transmission temps get about 170 the whole time.

C/K Man · November 17, 2022

I think a 10 speed will be a worthwhile upgrade for the L8T, even though I personally have been doing fine with an L96/6L90 for the past 10 years. As has my employer. I am just glad GM saw fit to use the 'Allison' 10 speed instead of the 8L90 or 10L90 in the HD trucks.

Now that GM has a base gas powertrain that is fully competitive with Ford's 2023 6.8L/10R100, I wonder if GM will come out with something competitive with Ford's gas 7.3L/10R140. There were rumors some years ago that GM was working on an 8.0L+ gas engine that was to be shared with Navistar, but I think that program fell victim to the whole Covid/supply chain fiasco (if it ever really existed).

Edited November 18, 2022 by C/K Man

nick112288 · November 28, 2022

On 11/17/2022 at 3:46 PM, C/K Man said:

I think a 10 speed will be a worthwhile upgrade for the L8T, even though I personally have been doing fine with an L96/6L90 for the past 10 years. As has my employer. I am just glad GM saw fit to use the 'Allison' 10 speed instead of the 8L90 or 10L90 in the HD trucks.

Now that GM has a base gas powertrain that is fully competitive with Ford's 2023 6.8L/10R100, I wonder if GM will come out with something competitive with Ford's gas 7.3L/10R140. There were rumors some years ago that GM was working on an 8.0L+ gas engine that was to be shared with Navistar, but I think that program fell victim to the whole Covid/supply chain fiasco (if it ever really existed).

You are correct about COVID killing whatever big block rumors there were.

GM would be really smart to come out with a big block, and as long as it was reliable and only a small price bump over the 6.6 make a killing.

2023 prices you aren't getting into a 7.3 for less than $5,000+ over the GM offerings.

Hell can't even get a F350 XL dually with the 7.3L. Have to get a XLT