2025 8.3L Duramax

[C/K Man]

Rumors at this point:

 

https://tfltruck.com/2024/01/gm-new-8-3-duramax-diesel-rumor-video/

[64BAwagon]

No longer a rumor

[C/K Man]

'TFL' ran a piece featuring some footage of test trucks spotted in Colorado recently, and speculated that these trucks may have been powered by the 8.3L Duramax:

 

https://tfltruck.com/2025/07/spied-are-these-the-new-2027-chevy-silverado-hd-gmc-sierra-hd-duramax-trucks-could-they-have-the-8-3l-megamax-v8/

 

A few days later, 'GMAuthority' posted word from a reliable source that the trucks were in fact powered by updated 6.6L Duramax diesels, and the rumored 8.3L is NOT planned for the HD pickups:

 

https://gmauthority.com/blog/2025/07/is-the-8-3l-duramax-megamax-hiding-in-new-silverado-hd-sierra-hd-prototypes/

 

FWIW, I think the 8.3L Duramax does exist and is in the pipeline, but I think it's for larger commercial trucks. 

 

 

[newdude]

13 hours ago, C/K Man said:

 

A few days later, 'GMAuthority' posted word from a reliable source that the trucks were in fact powered by updated 6.6L Duramax diesels, and the rumored 8.3L is NOT planned for the HD pickups:

 

https://gmauthority.com/blog/2025/07/is-the-8-3l-duramax-megamax-hiding-in-new-silverado-hd-sierra-hd-prototypes/

 

FWIW, I think the 8.3L Duramax does exist and is in the pipeline, but I think it's for larger commercial trucks. 

 

 

 

 

Those make the most sense.  8.3 for the 4500/5500/6500 and then updated 6.6 for the 2500/3500.  

[asilverblazer]

TFL and GMAuthority need to have an off the record conversation. Then publish new 'rumors' as needed.

 

Both current reports make reasonable sense, GMA suggesting such a jump from the current displacement isn't necessary based on the rest of the platform vs. TFL suggesting the displacement change allows emissions improvements without sacrificing and perhaps modest performance enhancements. 

 

The latter actually makes more sense to me. 

[carkhz316]

Betteridge's law of headlines

 

 

 

TL;DR: screw this sensationalist nonsense.

Edited August 7, 2025 by carkhz316

[Z45]

Unfortunately the internet is full of bogus news..

Edited August 11, 2025 by Z45

[Atlas]

On 8/6/2025 at 1:15 PM, asilverblazer said:

TFL and GMAuthority need to have an off the record conversation. Then publish new 'rumors' as needed.

 

Both current reports make reasonable sense, GMA suggesting such a jump from the current displacement isn't necessary based on the rest of the platform vs. TFL suggesting the displacement change allows emissions improvements without sacrificing and perhaps modest performance enhancements. 

 

The latter actually makes more sense to me. 

 

TFL survives on clicks and views. Anything they can do to get you to engage. Not that they don't have some decent content, but, they usually know as much as everybody else in the content creator space. OE's aren't confiding in them.

 

Does GM do appreciable volume with its Medium duty trucks? I always see them sitting on dealer lots, sometimes 1-2 model years old, still sold as new, just severely aged inventory.

 

I guess I don't see where an updated 6.6 wouldn't also serve their medium duty line. Why a bigger Duramax? And wouldn't an inline application start to make sense versus a V8? Cummins basically owns that medium duty space with its inline diesels, 6.7- L9

Edited August 11, 2025 by Atlas

[newdude]

35 minutes ago, Atlas said:

 

TFL survives on clicks and views. Anything they can do to get you to engage. Not that they don't have some decent content, but, they usually know as much as everybody else in the content creator space. OE's aren't confiding in them.

 

Does GM do appreciable volume with its Medium duty trucks? I always see them sitting on dealer lots, sometimes 1-2 model years old, still sold as new, just severely aged inventory.

 

I guess I don't see where an updated 6.6 wouldn't also serve their medium duty line. Why a bigger Duramax? And wouldn't an inline application start to make sense versus a V8? Cummins basically owns that medium duty space with its inline diesels, 6.7- L9

 

 

I think the theory behind the larger displacement is lower emissions.  Running the smaller displacement making the power they are now, combustion temps, EGR temps, NOX levels, etc.  Increasing displacement would lead to a larger, more efficient pump that wouldn't have to run as hot and be as polluting.  

[asilverblazer]

1 hour ago, Atlas said:

Why a bigger Duramax? And wouldn't an inline application start to make sense versus a V8? Cummins basically owns that medium duty space with its inline diesels, 6.7- L9

I think there is merit to the increased displacement for essentially 1 reason:

Lowering overall combustion pressure to lower combustion/EGT temperature to lower NOX.

If this is true, this suggests they are having more success with the DPF system efficiency compared to EGR or other NOX management strategies.  

[asilverblazer]

40 minutes ago, newdude said:

I think the theory behind the larger displacement is lower emissions.  Running the smaller displacement making the power they are now, combustion temps, EGR temps, NOX levels, etc.  Increasing displacement would lead to a larger, more efficient pump that wouldn't have to run as hot and be as polluting.  

Your reply was right before mine... so ditto.

Edited August 11, 2025 by asilverblazer

[Atlas]

Doesn't higher compression and higher combustion temperatures = more complete combustion, and a reduction in waste gases?

 

And why still a V8 versus inline?

[newdude]

7 minutes ago, Atlas said:

Doesn't higher compression and higher combustion temperatures = more complete combustion, and a reduction in waste gases?

 

And why still a V8 versus inline?

 

 

Lower temps are what's needed to reduce NOx production from combustion hence EGR to lower temps, SCR to clean NOx.  Diesels existing today is all about reducing NOx.  

 

Going inline would be serious coin and for what reason at this point?  

[customboss]

20 hours ago, Atlas said:

Doesn't higher compression and higher combustion temperatures = more complete combustion, and a reduction in waste gases?

 

And why still a V8 versus inline?

YES, everything but NOx because our non synthetic diesel ( and for that matter gasolines ) are crappy fuels.

NOx is result of efficiencies in combustion but the base chemistries of moderately processed hydrocarbons make it worse. I forget the calculations of using synfuels bases for fuel and resulting lower NOx. Its significant but with the current climate of burn it all to the ground no one can escape the economy of scale of developing exceptional engines that burn 1930's fuels tech. 

 

My brain is AI now...: its on the interwebs so its gotta be right....

 

Get Shell to use that NAT GAS FT base for fuels not engine oil and we could be burning clean with little DPF mess. 

 

 

Syn Fuels and NOx

Synthetic fuels can significantly lower NOx emissions, particularly when produced from renewable sources and used in modern engines. Studies have shown that Fischer-Tropsch (FT) diesel and jet fuels, which are synthetic, deliver dramatic reductions in major criteria pollutants, including NOx, due to their high purity and lack of contaminants. In a 2005 dynamometer study, the use of a Shell gas-to-liquid fuel with a combination particulate filter and catalytic converter virtually eliminated HC, CO, and PM emissions from diesel trucks, with a 10% ( THIS HAS TO BE WRONG I THINK AI MEANS INCREASE AS IN LOWER SFC)  increase in fuel consumption compared to conventional diesel. Research on a new synthetic fuel called hydroformylated Fischer-Tropsch fuel (HyFiT) demonstrated that it emits significantly less nitrogen oxides compared to fossil diesel in experimental tests using a van. Furthermore, studies on OME (dimethyl ether) fuels, another type of synthetic fuel, have shown substantial decreases in NOx emissions—up to 43%—when blended with diesel, especially when produced using renewable energy sources like wind power for hydrogen generation. The nearly 100% reduction in NOx observed in some studies is attributed to lower peak combustion temperatures and the use of large exhaust gas recirculation (EGR) quantities as heat sinks. However, it is important to note that not all synthetic fuels perform equally; one study found no difference in NOx emissions between e-fuels and today’s petrol fuel in lab or road tests, indicating that the emission profile depends heavily on the specific fuel type and production method. Therefore, while many synthetic fuels offer substantial NOx reductions, the outcome is contingent on the specific technology and feedstock used.

 

 

Edited August 12, 2025 by customboss

[customboss]

V8's used because Detroit diesel ( with Isuzu) can build a cheaper diesel with less rotational balance issues. 

 

To build a compression engine inline you get better efficiency and TQ capability.  But you'll spend more $$ on balance and machining quality and we all know how GM does quality lately......

Spoiler