Deep Dive: 2020 HD L8T 6.6L Gas and L5P Duramax 6.6L Diesel Engines

HondaHawkGT · March 18, 2019

On 3/13/2019 at 3:38 AM, C/K Man said:

It looks to me that the L8T is an iron block Gen. V without AFM/Dynamic Skip Fire. I see a lot to like in this engine, particularly the increased displacement, forged crank, and siamesed cylinder block with bored cooling passages. I would like to see E85 capability in the L8T eventually, but I think the 6L90 and 3.73:1 gear ratio will be fine. I hope the exhaust manifold bolts don't break under hard use, something I see in 6.0L's often.

As for the Ford 7.3L, I have questions! I looks like a good truck engine, but so for I don't see much that makes me believe it will have much of a future as a high performance/crate engine. While it certainly has displacement and the bottom end looks strong, the valve train doesn't look like it will tolerate very high r.p.m.'s. The valve stems and springs look very tall, and the pushrods are also quite long. Lots of inertia and I wonder about stability at high r.p.m.'s with an aggressive camshaft. The bore spacing is 4.65" and they are running a 4.22" bore, so it looks like the 7.3L also has a siamesed cylinder block. However, it appears Ford has machined slots between the cylinders to permit coolant flow between them. These slots are open at the top (block deck), which might be a problem if someone decides to hang a blower or turbo on one of these things. Heads look to have real decent porting, but I don't see a lot of cooling passages in them. These are just superficial observations, and I do think the engine will be good in it's intended applications. But it ain't no LS! Just don't see that kind of versatility in the 7.3L.

That's probably why Ford is trying to tamp down all the new hype from Ford fans that think the engine might end up in a Mustang. It's obviously not designed for a modern Mustang. GM has spent two decades slowly perfecting the LS family for both trucks and sports cars. Ford has a hard enough time going from one version of an engine to an updated version of the same engine. Restarting development of a pushrod engine after decades of trying to scrub their lineup of pushrod engines might be tough. Hopefully they kept a few of the old timers around that worked on the 351W. The fuel economy difference between this 6.6 and the 7.3 will be noticeable for sure.

L86 All Terrain · March 18, 2019

9 hours ago, HondaHawkGT said:

That's probably why Ford is trying to tamp down all the new hype from Ford fans that think the engine might end up in a Mustang. It's obviously not designed for a modern Mustang. GM has spent two decades slowly perfecting the LS family for both trucks and sports cars. Ford has a hard enough time going from one version of an engine to an updated version of the same engine. Restarting development of a pushrod engine after decades of trying to scrub their lineup of pushrod engines might be tough. Hopefully they kept a few of the old timers around that worked on the 351W. The fuel economy difference between this 6.6 and the 7.3 will be noticeable for sure.

Yeah I am with you, they wont be dropping a 700lb cast iron big block engine in the Mustang. They are all screaming Boss 429 already lol. I just want to see the look on their faces when their dreams are crushed. Maybe if Ford makes an aluminum version, but it is still a big block. If you look under the hood of a modern fiveoh, there is not a lot of room in there even with that small block DOHC engine. Has Ford released numbers yet? I guess around 420hp and 540-575tq on 87octane

Audew · April 9, 2019

Excited to hear this beast on the road soon. Does the estimated horsepower and torque ratings in the article probably at least 10% below what we’ll actually see from a big 6.6L monster?

i82much · April 9, 2019

I just hope Ford figured out how to get the spark plugs out of the danged thing.

troverman · August 1, 2019

Time to revive this topic, as Ford has released numbers for it's new 7.3L:

430HP@5500

475lb-ft@4000

Those numbers are a lot less than most people expected, although still more than anything else in a gas HD truck.

Something to consider though, is the absolutely simplicity of the Ford design. There is no direct injection. Ford is claiming the lowest friction of any engine in the class between the rings and cylinder wall. It uses a simple dual-equal VVT just like GM. It uses a variable displacement oil pump, and the internals appear very stout.

I think some people might be surprised at how fuel efficient it could be. But it doesn't shade the L8T by much (29HP and 11lb-ft). One advantage is that it will be coupled to the 10 speed auto in most applications, including all the pickups. But this is an optional, extra cost engine whereas the GM 6.6 is not.

Interesting, for sure.

i82much · August 1, 2019

Well if the Ford manages not to use any oil with those low-friction rings, then good on them. But I wouldn't want to be the first guy to buy that engine!

newdude · August 1, 2019

We finally got one in, but it wasn't one we ordered. Took it in on a dealer trade. Gas 6.6 in a WT crew cab. The L8T sounds like the L96 in terms of exhaust note. Definitely moves better than the 6.0. Needs a 10 speed though. Maybe because I've been spoiled with how those 10 speeds drive...

The 5 inches of wheelbase smoothed the ride a bit too.

troverman · August 1, 2019

4 minutes ago, i82much said:

Well if the Ford manages not to use any oil with those low-friction rings, then good on them. But I wouldn't want to be the first guy to buy that engine!

The Ford has a pretty low compression ratio, down in the 9's. It'll be fine...looks like its designed to last a long time.

First year engines can always be hit or miss, but the same goes for the L8T.

troverman · August 1, 2019

2 minutes ago, newdude said:

We finally got one in, but it wasn't one we ordered. Took it in on a dealer trade. Gas 6.6 in a WT crew cab. The L8T sounds like the L96 in terms of exhaust note. Definitely moves better than the 6.0. Needs a 10 speed though. The 5 inches of wheelbase smoothed the ride a bit too. Maybe because I've been spoiled with how those 10 speeds drive...

Well, its got +41HP and +84lb-ft, so it should move better than the 6.0L ! I'm hoping it has a burly sound to it. Although the 10 speed might help in some areas, I'm fine with the 6 speed. They are pretty bullet-proof and smooth.

newdude · August 1, 2019

51 minutes ago, troverman said:

Well, its got +41HP and +84lb-ft, so it should move better than the 6.0L ! I'm hoping it has a burly sound to it. Although the 10 speed might help in some areas, I'm fine with the 6 speed. They are pretty bullet-proof and smooth.

Correct on the power gain but the weight is up now 200-300lbs over a comparable K2 HD.

troverman · August 1, 2019

True, hadn't given that much thought. Probably the larger cab.

newdude · August 1, 2019

Just now, troverman said:

True, hadn't given that much thought. Probably the larger cab.

And 5 inches of frame, and all gas use the 11.5" rear like a K2 1 ton instead of the 10.5". But yes, they do move better than the 6.0.

newdude · August 1, 2019

Just now, troverman said:

True, hadn't given that much thought. Probably the larger cab.

And 5 inches of frame, and all gas use the 11.5" rear like a K2 1 ton instead of the 10.5". But yes, they do move better than the 6.0.

Kurt Pittatsis · April 11, 2020

Hi Everyone,

I see there are many good questions, thoughts, comments on here about the new gm hd trucks with the 6.6 gas. I also hear comments, questions, elsewhere in person and online about these new trucks but not many speaking from actual experience. I own one of these new trucks and have to say it has been great and love the truck, i purchased a 2020 chevy 2500HD LT Z71 crew cab with 6' 10" box with the 6.6 gas engine, w snowplow prep package and gvwr 10,650 lbs. I use this truck everyday for commercial use and tow trailers every single working day. The truck has performed beyond my expectations. Plenty of power and torque, capability and the fuel economy can be excellent, i feel this gas hd truck engine is a game changer in this market, i have put 22,000 miles on this truck and my best mpg was 21.9 mpg unloaded driving at speeds of 55 to 60mph, worst mpg 7.5mpg was pulling a 33ft travel trailer 9,000 lbs across north dakota with 25 mph + headwinds with gusts, average mpg highway unloaded is 18 to 20 mpg depending on fuel, wind, speed, driving habits other variables, average towing pulling rvs which drag tons of wind and hurt mpg greatly is 8.5 to 10.5 with 6,000 to 12,000 campers. I also changed stock tires for LT 275/70/18 cooper discoverer st (33") which is same size as stock but aggressive, my favorite truck tire the past 20 years. I have a 36 gallon tank and unloaded have drove up to and over 600 miles on a single tank.

On 3/16/2019 at 6:47 PM, redwngr said:

Hmmmm....

Thread title suggests both powertrains..

Kurt Pittatsis · April 11, 2020

Hi Everyone,

I see there are many good questions, thoughts, comments on here about the new gm hd trucks with the 6.6 gas. I also hear comments, questions, elsewhere in person and online about these new trucks but not many speaking from actual experience. I own one of these new trucks and have to say it has been great and love the truck, i purchased a 2020 chevy 2500HD LT Z71 crew cab with 6' 10" box with the 6.6 gas engine, w snowplow prep package and gvwr 10,650 lbs. I use this truck everyday for commercial use and tow trailers every single working day. The truck has performed beyond my expectations. Plenty of power and torque, capability and the fuel economy can be excellent, i feel this gas hd truck engine is a game changer in this market, i have put 22,000 miles on this truck and my best mpg was 21.9 mpg unloaded driving at speeds of 55 to 60mph, worst mpg 7.5mpg was pulling a 33ft travel trailer 9,000 lbs across north dakota with 25 mph + headwinds with gusts, average mpg highway unloaded is 18 to 20 mpg depending on fuel, wind, speed, driving habits other variables, average towing pulling rvs which drag tons of wind and hurt mpg greatly is 8.5 to 10.5 with 6,000 to 12,000 campers. I also changed stock tires for LT 275/70/18 cooper discoverer st (33") which is same size as stock but aggressive, my favorite truck tire the past 20 years. I have a 36 gallon tank and unloaded have drove up to and over 600 miles on a single tank.