We’ve already reported that the new GM 6.6L V8 engine for the all-new 2020 Chevrolet Silverado HD and 2020 GMC Sierra HD is assigned RPO Code L8T. We also were first to report specifications on the new engine. Now, let’s have a look at how the new gasoline engine stacks up against its predecessor – the 6.0L L96 V8.
| New 6.6L V-8 L8T | Outgoing 6.0L V-8 L96 | + / – L8T | + / – L8T % | |
|---|---|---|---|---|
| Horsepower: | 401 @ 5200 | 360 @ 5400 | +41 | +11.4% |
| Torque: | 464 @ 4000 | 380 @ 4200 | +84 | +22.1% |
The new L8T engine delivers 41 horsepower and 84 pound-feet of torque more than the L96, which translates to gains of 11.4 percent and 22.1 percent, respectively. But the good news doesn’t end there.
In fact, the L8T engine also delivers more power and torque lower on in the power band: the peak 401 horsepower is made at 5,200 RPM while peak torque of 464 pound-feet is made at 4000 RPM. Both figures represent drops of 200 RPM over the L96.
Overall, the L8T delivers notable improvements over its predecessor, delivering more power and torque at lower RPMs. In addition, the motor finally gives the Silverado HD and Sierra HD a modern powerplant, as the L96 it replaces was around for almost two decades.
About GM’s New 6.6L V8 L8T Engine
The new L8T gasoline engine features 8 cylinders and displaces 6.6 liters via an OverHead Valve (OHV) layout, otherwise known as push-rod. The GM engine is based on the automaker’s fifth-generation Small Block engine architecture initially introduced by the 6.2L V8 LT1, albeit with a few key differences.
Unlike other Gen V Small Black GM engines that have aluminum blocks (like the LT1), the L8T has a cast iron block. The other big difference is that the L8T engine has a bore of 103.25 mm and a stroke of 98 mm, while the LT1 measures in at 103.25 x 92 mm. Finally, the L8T’s compression ratio runs at 10.8:1, while that of the LT1 is 11.5:1.
In the 2020 Silverado HD and 2020 Sierra HD, the L8T engine is mated to the familiar GM 6L90 six-speed automatic transmission.
Subscribe to GM Authority for more L8T engine news as well as for ongoing GM news coverage.
Comments
Needs the 10 speed transmission….
I completely agree especially when you look at the competition like Ford with their new big gasoline V8 mated to the 10 speed. I will very likely buy the Chevy 2500 or 3500HD with the 6.6 Gas Engine when GM puts the same 10 speed behind it they are using with the Duramax.
My understanding is the 6-speed was selected due to its history of high reliability. There are many negative comments on the internet from owners of the newer 10-speed transmission behind the 6.2. When towing my RV, I’m happy to trade reliability for fuel economy.
It needs a ZF8 speed from Germany like you’ll find in the Ram 1500. Those transmissions are the best in the world. GM transmissions are garbage.
Kinda wish this were an option for the 1500 series.
That was an informative short story, didn’t say much but I’m sure they thought it was.
that is the ugliest thing i ever saw ram will be selling a lot more trucks ! ford, ram ,, chevy sorry!
Except that Ram still uses the 6.4, as well as will probably sell for more. Chevy offers more incentives in the HD series than ram or ford. The gas chevy will by far be more affordable and harder working, and most importantly longer lasting. Businesses and most farmers (the principle buyers of HD gas trucks) will prefer the Chevy for practical purposes. Private buyers would likely go for the higher end Diesel, and that is a whole new can of worms. It doesn’t help ram that the body isn’t new and that the Duramax has more power and a 10spd
Won’t take long for Ram buyers to find out how terrible their front end is. It’s sickening when to realize just how many Ram HD’s have low mileage death wobble issues. My nephew’s 2017 Ram 2500HD had death wobble problems by 10k miles. FCA threw parts at it for months before it mostly went away.
Mikecollins, The problem with front ends is the grease. To prove my point, look for the darker spot on the interstates a couple of feet after a bump in the highway. What is that dark spot? That is from both cars and trucks who are dropping grease onto the road after the vehicle hits a bump, from the flexing of the front end suspension parts. To solve that problem, do not use normal cheap grease. Use only a synthetic front end grease. Firstly, it does not drop off onto the road like normal suspension grease. Secondly, it is not affected by water as much as normal grease. The main reason to use a synthetic grease is because it is much better at lubricating the parts, thus less wear. Just as normal petroleum oil does not protect the engine parts anywhere as well as a full synthetic, grease is the same. I went and bought my own grease gun, put the tube of synthetic grease in it, wrapped it in two plastic bags and took it to my local oil change place and gave it to the guy to grease my front end parts. We used to drive about 200 to 300 kilometers per day, so all parts wear faster. Trust me, it make a huge difference to use the best lube stuff compared to normal petroleum lubes in your transmission, rear end, engine and suspension parts. It saves thousands of dollars on fuel use and engine life.
D.W. is caused by grease? more importantly .. the wrong grease? … you have no idea what your mouth hole is talking about.
Those spots are oil … dw is caused by several factors, none of which are grease issues.
Correct. DW is a BS artist. The NGLI # 2 (thick as butter) grease has too high a viscosity to be thrown off with a little jounce in the suspension. Warm or hot engine oil, on the other hand, will sling off easily.
The assumption that the grease is coming out of the joints means the joints have bad seals in which case, its not grease, its a defective part which is the original problem.
Chisler has had weak front ends, grabby windshield brakes and tranny problems for 40 years that I’ve been driving them. Youd think theyd learn, but I guess repeated bankruptcy and changing hands is not conducive to getting it right.
Dave SAE
Needs 10 speed transmission then I will by and if it is better then y not in 1500?
This is a game changer for many guys who don’t want the complexity of modern Diesel engines.
The 8.1 was eighteen years ago, with almost as much torque as the L8T. This isn’t amazingly new, this is where small block technology should be now. Still isn’t the diesel alternative. If GM can get 450 lb ft out of 87 octane in 2001 they can do a whole lot better than 464 in 2019 if they bring back a big block.
the 6.2 gets 460, and that is before a tune. This with a tune should get north of 500ftlbs, but half of the point of this engine is reliability. it is “detuned” to work hard with high efficiency for a long time, like 4800rpm for 30 minutes up a mountain. I drive a 2009 Silverado rated at 325hp and 350ftlb. I only use that power with 7500lbs up a 15% grade. I wouldn’t go that fast because a large load under speed is not safe. this is more power than I would normally need, thus Chevy probably didn’t feel the need to add much more. Honestly though, I am intrigued by the idea of tuning the new 6.6. 480hp and 520tq at wheels when it burns hot?
Cute sounding statement, but false.
Diesel engines are the same as gas engines, just with heavier pistons, rods, cranks and bearings to take high compression. Diesels dont have spark plugs so in that respect, they are less complicated.
The fuel system is not the engine and yes, its more complex.
A real Game Changer would be for you to get some education as to whats in engines.
dave SAE
With more and more useless sh!t getting put on the half ton pickups (auto stop/start, cylinder deactivation, etc) this engine makes a strong argument to go a 3/4 ton daily driver, just for less complexity. If it has the dynamic skip fire tech on it I can live with that, just hate the deactivation systems of yore.
That engine is waiting for me in a GMC work truck as my daily.
The L8T would be nice update for my 68 Impala.
Or an Alpha-based 2021 Impala……
Hopefully an Alpha based Impala..?????
I wonder why they use the high compression 6.2 with 420 hp in the 2500. Just my 2 cents.
correction why they didn’t want to use the 6.2
Because the L8T is an iron block engine which is more durable and better for truck use. Plus it will put out more torque at low rpm’s while being less stressful on the engine.
Why hasn’t Ford used a 5.0 Coyote or 3.5 Ecoboost in an F-250 yet??? Supposedly the 3.5 Ecoboost pulls like a diesel, so why not use it in a Superduty?
Not strong enough
Unlike the 6.2 liter engine, this 2020 heavy duty truck engine is designed for pulling a very heavy trailer. The 6.2 does not have water jackets between each cylinder, so it runs too hot when users run on propane. Even though both the the 6.2 and the newer 6.6 have siamese cylinders, there are small water jackets between each cylinder in the 6.6 liter. This means GM can market the HD cast iron 6.6 liter engine to marine and industrial users which prefer to use high octane, cheap, clean burning propane. The old 8.1 liter big block ran too hot on propane because it had siamese cylinders with no water jackets between each cylinder. That is why GM designed a brand new big block, the 8.0 liter in 2010, that had full water jackets between each cylinder. The 8.0 was never installed in any factory production line GM truck, because a few months after they developed it, GM canceled the production of medium duty trucks and bus chassis. Freightliner uses the 8.0 liter engine in school bus chassis that can use gasoline or propane, but most school boards prefer propane because they can get long term fuel contracts at a very low price compared to diesel fuel.
Never knew about the 8.0 but the 8.1 was a beast. Probably my favorite gasser. I wonder if it can be revived since we’re back in the medium duty game? Small blocks are great but I love BBC’s.
MATT, You need a second cup of coffee. Read my comment once again above for the reason that GM designed and built a replacement for the big block 8.1 liter and the water jacket thing in the 8.0 liter.
Chevy had hinted about bringing back the 8.0 in a couple of years. In an answer to Fords 7.3 gasser.
Gasoline burns hotter than propane.
That’s why a generator makes more power on gasoline versus propane.
Regular pump gas does not have as high octane as propane does: propane octane rating is approximately 103-110.
The highest pump gas that is readily available around here is 93.
You need to look at the BTU of feul to know which one burns hotter.
Stop misleading people.
It seems kinda stupid to pair up a new engine with such a lousy 6 speed transmission. It should be at least an 8 speed and preferably a 10 speed. Chevy seems to always be behind the curve. Our 4 speed was a good transmission but the 6 speed we have now is lousy.
Personally a 4-speed/OD is the best transmission for American roads as I had plenty of 4-speed/OD cars and SUVs at 80mph getting 21-30 mpg with cargo/AC on.
Unless we get 90s Montana “Reasonable and Prudent” unrestricted speed limits in low populated States I see no reason to have more than 4-5 gear automatics. With that statement, yes a 8-10 speed need to be offered.
Ford’s new 7.3L V8 is PFI, not direct injected, cast iron block and is paired to new Ford-designed 10-speed automatic for HD trucks.
No power numbers yet from Ford.
ford use 10 speed because the 7.3 pump out 400 ftlb of torque at 1500rpm all the way toward 475ftlb at 4000rpm. so the transmission could shift more often to keep the rpm low.
i guess gm 6.6 only hav 340-350 ftlb of torque at 1500rpm and 400ftlb of torque comes in at 2000-2200rpm so gm plans to keep the rpm high(2200-4000rpm powerband). 10 speed might be overkill for HD truck. unless drive empty unloaded all the time.
With as much torque as this engine has got a 4 speed just might do the trick.
Or better yet a 3 speed on the column!!
This truck is going to be sales success with big work fleets and retail customers who wants a powerful diesel alternative.
This truck will be cheap to run.
Obviously the comments above about a 4 speed transmission being enough is stupid. This engine is not for pussy driving in a 2500 or 3500 series pickup truck, it’s for pulling a trailer that weighs twice or three times what yur punny little SUV weighs. Ask any commercial trucker, you can never have too many gears and when empty with no weight on the back, you skip shift, just like the brain in AOC.
That is one ugly ass truck, Sad, I was a loyal GM fan for 20 years, what the hell is GM thinking, oh wait, they are not thinking. Or the designers and managers are just really really dumb!
I just got off the phone with the GM Fleet rep for southern Alberta. I asked about the 2020 GM 2500 and 3500 pickups with the 6.6 gas engine. The 6.6 liter gasoline engine is an extra cost option over the standard 6.0 liter carryover engine from the 2019 models. No price has been set to get the optional 6.6 gasser. You can place your order for the 2020 crew cab gasser now but no orders will be accepted until late May for the regular cab or extended cab models with the 6.6 lier gas engine. The 464 pounds feet of extra torque for the 6.6 liter gas over the 6.0 liter gas engine is either 104 lbs feet more of 84 lbs feet more., depending on the GVW rating. The much higher compression ratio of 10.8 to one ratio for the 6.6 gasser will make a huge difference if you run 105 octane propane or CNG, which has an even high octane rating.
REVISION OF ABOVE COMMENT BY ME: The phone call i made to the GM Fleet rep for Alberta, said that the 6.0 liter gas engine would be the standard engine for the 2020 GM 2500/3500 trucks and the 6.6 liter was an optional gas engine. He sent me an email today to say that is wrong. In fact the STANDARD ENGINE IS THE NEW LT1 based 6.6 liter gas engine for the 2020 2500/3500 trucks. Of course it’s a heavy duty engine and it is cast iron type, not aluminum.
I own a 2020 2500HD diesel Denali, I thought for a split second about a gasser, but like others have mentioned, a “six speed” really! I know a guy with the 6.0 liter 2500, the truck is used and abused and keeps on ticking, GM wanted tough and reliable…likely they will get that out of this engine, but the transmission choice killed any thoughts of me getting one. My experience pulling a 6800 lb travel trailer on two 600 mile round trips with the Duramax and 10 speed Allison…game changer. Doesn’t even know the trailer is behind it, even on grades, and the transmission is so smooth you can’t even tell when it shifts. I had a 2019 diesel Denali before this one with the 6 speed Allison, it did the job, but it shifted kinda hard compared to the 10 speed. For what it’s worth, when the gasser gets an 8 or 10 speed, might fit some folks.
I’m getting the gas v8. i’d rather have a big block though.
why are the valve stem seals a different color in the the 6.6l gas engine when you compare the exhaust valve to the intake valve?
I feel it’s a wash between the 6.0L vs the 6.6L because of the added weight of the 2020-2021 trucks. You’re not gaining anything.
Your gaining a ton, almost literally in towing power. The new HD doesn’t weight 15% more, which is the increase in power, and ilthe 6.6 makes that power much lower than the 6.0 did. Its weight increase is negligible when you look at gross combined weight ratings of truck+trailer. It will tow your same weight trailer much we easier, and more efficiently as the huge grill is more aerodynamic than your trailer is, even though it takes a hit riding empty. The new engine is also about 20% more efficient, so you’ll see a 1-2 mpg improvement empty and dito loaded. It also costs almost nothing more to make and buy. Way cheaper than ford’s new 7.3.
LOVE MY 2021 CHEVY 2500 6.6 WITH 8 SPEED AUTO ….PULLS BETTER THAN OUR LAST DURAMAX AND 20,000……CHEAPER………PULLS 30 FT. HORSE TRAILER LOADED WITH NO PROBLEMS …..
You’re obviously a dumbass by that comment.
Like seeing the chat about difference in engines. To the comment about the transmission not being good, I have read that in 2024 models the transmission is now an allison 10 speed transmission. my question did they fix the other problems with the alternator, etc