6.6L V8 L8T GM Engine Specs Released40
Last week, GM Authority was first to tell you that the new 6.6L V-8 GM engine for use in the all-new 2020 Chevrolet Silverado HD and 2020 GMC Sierra HD was assigned RPO Code L8T. Today, we have specifications of the new gasoline mill.
Here are the basics: the L8T 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 V-8 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 in the stroke: the L8T 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.
Without any further ado, behold the specs for 6.6L V8 L8T GM engine.
|GM RPO Code:||L8T|
|Type:||6.6L V-8 gasoline|
|Bore & Stroke (in / mm):||4.06 x 3.86 / 103.25 x 98|
|Block Material:||Cast iron with nodular iron main caps|
|Cylinder Head Material:||Cast aluminum|
|Valvetrain:||Overhead-valve, two valves per cylinder, variable valve timing|
|Fuel Delivery:||Direct fuel injection|
|Power (hp / kW @ rpm):||401 / 299 @ 5200 (SAE certified)|
|Torque (lb.-ft. / Nm @ rpm):||464 / 629 @ 4000 (SAE certified)|
|Predecessor:||6.0L V8 L96/LC8|
In the 2020 Silverado HD and 2020 Sierra HD, the L8T makes an SAE-certified 401 horsepower (299 kW) at 5200 RPM and 464 pound-feet of torque (629 Nm) at 4000 RPM. It will be mated to the GM 6-speed automatic transmission (6L90) driving either the two rear wheels or all four wheels.
Stay tuned to GM Authority as we learn more about the L8T, and for more GM news.
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What kind of fuel saving technology is available in this engine? honestly fuel consumption is large with these titanic machines, and it stinks having to upgrade to the diesel when diesel is so expensive compared to gas, not that the increase in engine cost was enough. AFM? DSF? Atkinson cycle? the increased stroke and compression ratio will be highly appreciated, but honestly id rather a good gas engine than a diesel anyways. Shame the transmission didn’t get upgraded to 10 or even 8 speeds.
Still chasing this very topic down. Will report more once we get something concrete.
No AFM or DFM on this engine.
It has Direct injection and Variable Valve Timing. Trucks are too heavy to take advantage of AFM.
Officially confirmed: no AFM, no DFM, and no ASS. Also have the octane rating:
If this engine does not have any AFM is it an omission that those engine features are mostly for EPA appeasement, not long term durability? I would love to permanently disable AFM on my truck. I will do it once the warranty expires.
You can easily disable AMF with a osb device (truck thinks that you’re driving loaded), everytime you take your truck for service just unplug it and no one will know it was there.
I’m kind of excited about the HD trucks. It proves the General still can when they want to. The Chevy is a little hard to get adjusted to and I’m sure the interior won’t compete with a RAM but where a trucks true worth is proven, hauling and towing, these new HD’s should shine!
ATTENTION EDITORS: You forgot to mention one very important fact. One of the truck related videos on YouTube showed the GM engineer saying that the HP and torque numbers were based on regular 87 octane gasoline. This is much different than the GM car engines test specs as GM always tests the engines with 93 octane Super premium gasoline. Assume this engineer was telling us the truth, ( maybe he mispoke ) if the new 6.6 liter ( 400.69 cubic inch ) with 464 lbs feet of torque, will make much more power on the same 93 octane gas. GM shows an increase of 5 lbs feet on the late model 4.3 V6 with a 10.5 to one compression ratio. The standard torque is 295 lbs feet on 87 octane gasoline but they show a torque of 310 lbs feet on premium gasoline. The same 4.3 V6, showed a torque of 325 lbs feet when GM used E85 gasoline which has an octane of about 95. So, based on the GM testing, with a much higher CR of 10.8 to one on the new 2020 6.6 liter engine, that 464 lbs feet of torque will rise about the same 10.2 percent on E85 as the 4.3 V6 did, or….TA DA……511 lbs feet of torque. It might be even higher than that because of the much higher CR on the new 6.6 liter engine, possibly about 520 or 525 lbs feet of torque. OK, for the HP number from 401 bumped up 10.2 percent and you have 442 HP. Not too shabby. OK, do the math, the new E85 gas HP and torque number on the 6.6 of 520 lbs feet at 4,000 RPM will equate to 396 HP at 4,000 RPM. Put in a hotter cam, get another 10 percent HP and that 396 HP at 4,000 becomes 436 HP at just 4000 RPM. That’s not the max HP, just the usable HP on a day to day basis that you will reach if you floor the gas pedal towing a 6000 lb trailer. The same ratio of power increase for MAX HP, will be…….TA DA…….at least 486 HP at 5,300 ( 5,200 ) RPM. Remove the exhaust system resonators and get another 2 to 3 percent power and that 486 HP number goes to about 501 HP. Are you happy now???
Today i talked to Callies Crankshafts in Ohio to find out the longest stroke that can be used in the new design 2020 GM 6.6 liter Gen 5 block. A Callies Magnum forged crank of 4.125 will fit both the LSX and LT Gen V blocks. With a bit of grinding by hand or machine, a 4.125 inch stroke can be used. This will bring the stroke from the stock 3.858 inches up by just over a 1/4 inch or by 0.267 inch. This will give a couple more cubic inches than the previous 4.1 stroke calculations that i have posted under various L8T articles on this website. It will now be 428.428 cubic inches or 104.775 mm stroke. It’s an increase from 425.8 cubic inches, not very much, or about 3 cubes. By the way, the suggested list price of the Magnum 4.125 inch forged crank is about $1800. A billet Callies crank is about $3,300 for the same stroke for the Gen V LS.
ARE WE DOING THE ALL CAPS THING NOW? OKAY!
Now then: we did not “forget” anything. What we did is confirm the info with GM prior to publication, as a responsible news outlet should. Here’s some info for ya:
One thing you need to consider is the 3/4 ton and up truck have much more lax mpg regulations. This is why MFGs have turned so much more development on these trucks.
I almost see the mid size taking filling the light truck segment and the 3/4 ton replacing the 1/2 ton as the norm.
If not I am not sure how the 1/2 ton survives as things get tougher with even more harsh regulations.
Get federal and state and sometimes municipal tax breaks by running your new 2020 GM 2500 or 3500 pickup or chassis cab on very cheap propane. The truck or rail car load of propane LPG is just 73 cents per U.S. gallon ( 3.7854 liters ) last week. if you have a contract with a propane supply company and you have a small fleet, they will probably sell it you for just $1.50 to $1.60 a gallon. You leave the gasoline system in place and we just add on a complete different propane full system wired into the factory computer. It starts on gasoline and after 2 or 3 minutes, when the engine water gets up to about 80 degrees F, ( adjustable ) it switches over to propane automatically. Since propane is 105 octane ( R+M ) rating, the engine computer advances the timing father than if you are using lower octane 87, 89 or 91 octane gasoline, so you get better MPG and about 5 to 8 percent more torque and HP with the 10.5 or 11.5 compression ratio pickup truck engines sold now. You actually get better MPG on propane now than the lower compression ratio engines of 6 years ago, even though LPG propane has a lower BTU amount of energy per gallon, compared to gasoline. Some states offer a full sales tax rebate if you get a propane vehicle conversion. The federal rebate for propane vehicles was 50 cents per gallon last year, not sure what it is for 2019.
This engine VS the ford 7.3l? How do they stack up???
The 7.3 replaces the Triton V10 and the 6.6 replace the truck 6.0. I’d said before here that the 6.6 isn’t a big block replacement and wonder will GM have an 8.1 replacement?.
On a sidenote can anyone imagine if the Caprice made it to 2020 we would had a 6.6 option with 10-speed?, or (more realistically) a 6.6/10 speed Express van?.
I don’t see the 6.6 coming to the Express and Savana TOO soon. Didn’t the 350 stick around for a few years after the HD 6.0 came out in the early 2000s?
I probably won’t count the Express/Savanna out completely because the 6.0 won’t be economicaly feasible anymore after a few years. IMO They can go back to a 2 v8 strategy with 5.3 on the lower models and 6.6 in conversations/cutaways in addition to 4.3 v6 and Duramax 4-6 cyl..
kudos to GM on the cast iron siamesed-bore block. Cheap 396 and 427 for the masses!
It has the same heads, and I assume intake manifold and camshaft as the L86. I fully expected 420 bhp and 480 lb-ft. Perhaps it has a smaller cam for better low end torque, which isn’t revealed by peak numbers only?
fun fact: if you put LT1 pistons in the 6.6, you get 12.2:1 compression. That is a meaningful increase in efficiency, especially with LPG (which has an octane of 130+).
The North American grade of auto propane is HD5. It’s R+M octane rating is 104.5, but often quoted at 105. CNG has an octane of 120 R+M. The GM engineer responsible for this development of the 6.6 said it’s based on the Gen V, which is an LS type engine. The bore is exactly the same as the 6.2 liter at 4.0649 inches, but with a longer stroke of 3.858 inches. Callies makes a stroker crank for this block with a max of 4.125 inches if you hand grind the lower part of the cylinders to clear it. Obviously new pistons for the engine are probably a slightly different material to be stronger. There are mini water holes or jackets between each cylinder, but it basically is a siamese type cylinder, except for the extra cooling of the water jackets between each cylinder. This is why it can run on propane without overheating. Remember this engine will also be used as an industrial engine in forklifts and power plants, so they can run a milder cam to bring the torque of the max RPM to below 2,000 RPM.
The purpose of the HD trucks is to haul cargo and pull trailers not turn them into race cars. The diesel engine is the best option because of the high torque at low RPM.
Build it in an extended cab model and I’ll consider ordering one tomorrow…..QUICK! ! !
You can’t order them. Yet.
Have to see how the 7.3L Ford and 10 speed compare.
The torque on this motor is @ 4,000 rpm, a little too high for me.
The ford makes a negligible 4% more torque than the 6.6. also, the 6.6 is tuned a little lower than the ford. also that max torque at 4000 rpm doesnt mean you have no torque at 2000 rpm. youll have over 400ftlbs at 2000 rpm, so dont worry about running it hot unless you need to climb a 13% grade.
This is a great engine for a work truck! I like that GM is focusing on what makes money instead of worry about what a few dozen buyers want! People on this site forget that the Bill’s have to get paid and trucks like this have huge profits and allow for cars like the Camaro and the Corvette.
The engine does not need 500 hp 500 to it needs to run for hours at a time without having cooling issues.
“trucks like this have huge profits and allow for cars like the Camaro and the Corvette”
ROFLMAO… you mean it gives Barra a 22+ MILLION $$ bonus for Barra while killing jobs. This truck/engine has nothing to do with a Camaro or ‘Vette Brian the delusional…
No you are! Profits are used to create the Camaro and Corvette! Without profits these low volume cars can not and will not get designed or built!
Do you now see the connection? Or do I have to explain it like a child to you!
Actually, the Corvette is extremely profitable. The Camaro is also profitable, but to a lesser extent.
The notion that one vehicle program (pickup/trucks) funds a disparate vehicle program that is unprofitable (Corvette or Camaro) within an automaker only exists in the minds of those who haven’t worked for an automaker and taken part in product planning. Now, there are exceptions to this, with NEV and AV efforts being the most prominent… but these are seen as medium and/or long-term investments and therefore are allocated available capital. The Camaro and Corvette are not long-term investments. They are products to make money HERE and NOW.
Bottom line: if Camaro or Corvette were not profitable, GM would not think twice about discontinuing them… as it already did after Gen 4 Camaro. The current GM executive management team has shown that it has no sacred cows. Heck, it sold Opel after owning it for nearly a century while killing all the passenger cars on which the new GM staked its renaissance.
Thank you very much Alex for your confirmation! After doing the research I knew what you confirmed but simply didn’t feel like arguing with Brian the delusional.
I never said the Corvette or Camaro was not profitable! I said GM uses profits from trucks to fund other cars! Most notably the Camaro and Corvette! If you dont believe this happens then you are a fool!
The Camaro and Corvette are not mainstream volume models, they only sell in limited numbers compared to say a car, cuv, SUV! GM could operate just fine without a Camaro and Corvette. I am glad GM decides to build both, as other manufacturers refuse to build two great performance cars.
So the next time you feel like schooling somebody why dont you do a better job of it! Like reading what I said and adding things up to further your point!
Well well Brian, look who’s been schooled like a child, lol….
Right from the engineer’s mouth on the new 6.6L. I love when engineers explain the new product.
Musings of an engine enthusiast…
Can no compromise and siamesed-bore be in the same sentence (or paragraph?) I know the block material is different, but there weren’t too many 400 cid motors on the road for very long back in the day. The regs have hobbled diesel technology so badly that we’re back at gas again to move big stuff. Kind of ironic isn’t it. Reliable and efficient diesel engines forced to be so overly-complicated and high pressure. Loved my DD 6.2l (25 mpg all the time) Suburban and 5.9l (non-siamesed) 12 valve Cummins. Couldn’t CNG or hydrogen be used to assist diesel burn and eliminate aftertreatment? How many resources are used to produce and maintain the aftertreatment that reduces the reliability and efficiency of an engine by its mere existence? Saving my pennies for the new big block that will be introduced this year though. Nothing has ever matched the sonic beauty of the noise they make. Also looking forward to Achates down the road if it can be kept simple enough. Guess I’m old school, but then again 472 and 500 are my favorite numbers.
Ed, scroll up to see the of comments made about the new design big block. It was designed in 2010 but never installed in any GM vehicle. The engineer said that the new 2020 6.6 liter gasoline has mini water jackets between each cylinder but basically it’s a siamese cylinder. If, if, if, they cast the block of the 6.6 liter gas engine as a high deck block, like the LSX cast blocks, then you can put a 4.5 inch Stroke crank in it, to bring the cubes up to about 441 or so. See all did the math i did in my other few comments above. The 4.25 or 4.5 stroke would be still an LT type engine or small block. I think it worked out to be a 7.8 liter with the 4.5 stroke, but again see ALL my numerous comments above.
Thanks Mark, I went back and looked at your comments. But we are still looking at a 4.4″ bore center block right? I just prefer an engine with larger centers. My favorite muscle car era engine (472/500) has 5.0″ centers and is a bulletproof high nickel design circa 1968. Weighs about 50 lbs more than a SBC. The bottom end features a 2-bolt main and cast crank, yet can handle over 1,000HP (some say 2,000.) The reason I’m looking forward to the new 445 cid is that it appears to be a simple yet modern big block. Stuff like rod ratios, simplicity of design (read no DI), reasonable CR, and area under the torque curve from say 1000 to 2500 RPM matter most to me. Torque specs at 4,000 RPM is something for the Marketing Department. I want 300k+ mile durability without burning oil. I also like the immediate throttle response of big cubes. I NEED simple when I’m driving a Penske truck from coast to coast in the middle of the night. I did that recently with a 6.0, and do admit that engine is very impressive. It’s just that I believe you can push beyond the ‘sweet spot’ of certain architectures/designs especially when you’re talking about medium-duty applications. I think siamese bores are an indication that the bore centers are too close. I hope the 6.6’s wind up being super-reliable high-mileage motors. Thanks!
The japanese are experimating with hydrogen with the diesel engines and say very low emissions. The lack of a hydrogen infastrucure is probably holding GM back ?
I’ve had the 6.2 litter engine in my 1500 Sierra’s since it came out. I buy new every 2 to 3 years. I pull a 30 ft travel trailer all over Montana so lots of ups and downs on mountain roads. The 2020 1500 eliminated tow mirrors as an option. I will not depend on cameras for towing. I will probably go to the 2500 HD in 2020. I can’t decide on the engine — the new 6.6 gas or the diesel. It appears I will lose HP and torque if I go gas, as compared to my 6.2. Recommendations?
BRENDON, You are wrong about the power drop between the 6.2 and the 6.6. liter 2020 gas engine in the 2500. It has a touch more torque at a lower RPM than the 6.2 liter. By the way, the 6.2 should not be hauling a 30 foot trailer unless it is super light. That’s according to the GM recommended max towing. Spend a few dollars and get a port fuel injection propane system added to any engine. Leave the gasoline system in place and you will then have two complete fuel systems. A shop close to me has done more than 15,000 auto LPG conversions and was the first to use a port fuel injection for propane. Gasoline and diesel fuel are climbing and will keep going up at the pump price, so propane looks very attractive over the life of the next year. A propane conversion makes the resale value of a used truck very attractive, especially on the west coast of both Canada and the USA. If you want, i’ll post the name and phone number and website of the best propane shop this side of the midwest. All tuneups, aside from spark plugs, are basically a software adjustment, which can be done over the internet from the conversion shop, with a laptop plugged into the outlet under your dash. . Unless you have a auto propane retail location within 10 to 15 miles from you, it may not be worth the time, unless there is a propane distributor close to you. They are very interested to promote auto propane, so they might give you a special price. Most of them are only open during a normal business day and close at noon on Saturday. Trust me, you will love the high 105 octane rating of propane. My three fleets have run over 25 million miles ( 40 million kms ) on propane, so i know a thing or two about the world’s greatest fuel. Your engine will last twice as long running on propane compared to gasoline, with a savings of 40 to 50 percent on the cost of fuel.
Mark — thanks for your comments. So does the added torque make up for the loss of HP? Propane is an interesting idea but I don’t want to take up the room in my bed for a tank. Also, don’t know anyone who does that kind of work in my area. Never had a problem towing my trailer — it is light and 1/2 ton compatible.
It is good concept to perform aggressively against a passive opponent in purchase to steal much more blinds. Sometimes, you are required to make pressured bets at the beginning of the spherical to make the game more thrilling.