Why The Gen-V LT Outshines The LS

[petethepug]

Oh, this has gotta hurt!

This Cadillac Escalade V-8 Failed After Just 4 Miles — Motor1.com

General Motors is under investigation for a string of engine failures. New cars shouldn’t have engines that fail after just a few miles. However, one 2023 Cadillac Escalade suffered a catastrophic failure with just four miles on the odometer. A new video from Dave’s Auto Center attempts to...

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[Marky Dissod]

VVT, DOD & DI are all technologies that provide additional tuning benefits, but that add complexity expense & failure points to the engine without a benefit significant enough to compensate for it.

As these technologies were added to the LS the engine became less reliable but removing that tech was easy & restored the former benefits to the engine;
if the LT is to ever become a staple like the LS it will be because of the ability to affordably ditch the unreliable aspects & simplify the processes back to a reliable engine that can handle significant performance increases without falling apart.

What works is what works, all the claims about advantages with the more involved technology never matter if the added failure points nullify the benefits.

You can hit & maintain a target AFR consistently with computer controlled port fuel injection, the injectors do not need to be introduced to the combustion chamber & its DESTRUCTIVE environment to achieve a reliable AFR;
it just costs more to develop injectors that will work in a combustion environment & it reduces their lifespan to move them to the combustion chamber.
VVT can expand the optimal rpm range of the cam profile beyond a static ground cam but not without adding cost & reducing reliability to a point that nullifies the benefit,
DOD is just a gimmick to please the EPA that provides no real advantage in exchange for its failure prone design

Not sure if I agree with you on Variable Cam Timing (it varies the cam which varies the valves).
Guess the deciding proof for me would be to take an L92 / L9H, disable the Variable Cam Timing,
custom grind and install a cam meant to meet or exceed ALL the performance targets hit by the GM OE cam with its VCT active,
and if the custom grind 6.2L performs as well or better than the GM OE 6.2L, then I'll agree with you that GM's VCT is worthless.

Direct injection and Cylinder Valve Deactivation, yeah, those features are bugs;
I'm convinced they were designed and installed with the express intent of harming the Gen 5 / LT V8s' durability / reliability at or past 175,000 miles.
Put another way: GMT800s and early GMT900s are hurting GM's bottom line.

 

[RET423]

I didn't say VVT was pointless, I said it expands the optimal rpm range the cam can deliver over a cam that has a static grind

But to gain that expanded optimal range comes at a cost of more moving parts & more complex system to apply the changes on the fly to gain that benefit

The gain compared to the cost in dollars complexity & additional failure points/reliability don't make sense in a real life application; the regular person who operates a VVT engine would experience little to no difference if that same vehicle had the VVT removed

If the system never fails while they own the vehicle it's no big deal but over time increasing failure points are chickens that will come home to roost, the manufacturers know this so they delay these things as long as they can; but government regulations eventually push them to implement tech that increases the cost of their products & reduces the reliability at the same time

 

[Marky Dissod]

I didn't say that you said VVT was pointless.
To avoid crisscrossing my inferences with your implications ...

I'm of the EXPERIENCED opinion that
V4 mode is a liability not only because of how it fails, but how it ages - BADLY.

Any-cylinder-deactivation WORKS better than V4 mode, ages a wee lil bit better than Engine Half@$$,
but when it fails, how many cylinders does it even halve left, and for how long?

Don't think VVT is not a liability as it ages, seems to age gracefully with little to no degradation.
Don't know enough about how it fails to render my verdict on it yet.

Direct injection is a disappointment, given that it can't / doesn't keep intake valves clean.
It does not appear to have enough of a history of failure, YET,
but GM can tungwipe my kornwhole for the cost of replacing those direct injectors.
I know that there are port injected versions of these engines in aftermarket development.

 

[rdezs]

As for GM's VVT, it's proven to be quite reliable and effective. Let's not forget that it allows you the best of both worlds to some extent. Not too long ago, if you wanted to pull a heavy trailer you went for the RV cam that gave you the low-end torque, but sacrificed high-end horsepower. The guys wanting the high-end horsepower had no low end torque, and an erratic idle. And good luck getting a heavy trailer rolling with one of those cams. The VVT is a very good compromise for real world drivability and function. And it's one of the reasons you can get 20 miles per gallon out of your 6.2 while having over 400 horsepower.

The LT.... I think they broke one of the most basic rules. Don't mess with something that works real good. At some point you make things so complicated, it drastically affects reliability. I have a generation one SBC in a Jeep CJ7.... And it's the one vehicle in the stable I would trust wholeheartedly driving to Alaska. The electronics on today's vehicles are troublesome to say the least.

 

[RET423]

VVT has the capacity for great things but GM uses it to enable EGR without an EGR system, the hold the exhaust valve open momentarily when EGR is commanded to injest exhaust back into the cylinder

Because of the application I thinks it is a waste of technology that damages the engine like all EGR schemes even as the components themselves are not as unreliable as say DOD lifters

I think that cylinder deactivation is without value even if it could be implimented in a reliable way, it's intellectually offensive to think the same vehicle at the same speed in the same circumstances will require less energy to do the same work if some of its cylinders are shut off while the active cylinders drag them along than it would with all cylinders contributing; it's an expensive gimmick that has damaged GM's reputation & deservedly so.

Had the LT never been developed these technologies would not be doing any better on the LS platform, bad ideas get bad results

 

[Marky Dissod]

VVT has the capacity for great things but GM uses it to enable EGR without an EGR system,
the hold the exhaust valve open momentarily when EGR is commanded to ingest exhaust back into the cylinder.

Sounds like at least some of this 'internally insidious EGR activity' can be tuned out, or mitigated by tuning?

 

[RET423]

I don't think it can be eliminatedwith the stock cam grind but it likely can be reduced to a small amount by disabling the VVT

If the aftermarket ever starts developing VVT performance cams & the tune can be tweaked to capitalize on it the pre VVT engines will be relegated to dinosaur status, done right you can get a near flat torque curve with VVT & a cam ground to use it

 

[rdezs]

I couldn't agree more on the AFM/DOD. I saw an increase of about 1.5 MPG by deleting it. My wife commutes 50 miles a day round trip, on a 55 mph State highway. It was frequently running in V4 mode.

The self-induced EGR. Perhaps a software or hardware limiter to prevent the VVT from retarding the final two degrees? Just a thought...