Understading VVT

[donjetman]

https://www.lsxmag.com/tech-stories/l8t-to-the-party-using-vvt-to-our-benefit/

 

[Marky Dissod]

At the moment, I'm getting several '404 Forbidden' across at least three different websites looking for that article.

 

[Joseph Garcia]

Excellent article, IMO. Thank you for sharing.

 

[Fless]

At the moment, I'm getting several '404 Forbidden' across at least three different websites looking for that article.

No problem here clicking on the link and getting to the site. Tried Firefox and Edge and all is good. Why are you searching for the article on different websites?

 

[Marky Dissod]

'cause the lsxmag link no workie.

For some reason, my Opera will not let me view these articles anywhere, but FireFox lets me read ...

 

[Marky Dissod]

I get what the article is saying, in principle.
Most of us are not using cam lobes so large that we can't use VVT - so why NOT use VVT?
(It's really Variable Cam Timing, but whatever.)

Say something 'dumb' goes wrong with our 'VVT' feature. Where does it wind up?
Fully advanced? Fully retarded? Somewhere in the middle?
Is it possible it could wind up 'stuck' somewhere other than 'expected'?

 

[Foggy]

In my understanding the VVT Allows the OEM's to use a smaller camshaft
(lower duration) which is basically what they've always used. So that's why
us hotrodders always went with "bigger" cams for more power... With the expense
being poor idle/low rpm behavior which the OE's can't do due to lots of reasons.
Our Gen IV engines can only "retard" the cams position in relation to the crank...
Which makes it "ACT" like a larger camshaft but when/where/how it gets retarded
is now controllable by the smart ecms.
To me there isn't really a downside to our VVT except it does add a something else
that can wrong as stated above...
That being said, if the VVT components were to get "stuck" in a certain position it
would be in the ZERO position which is default - which means no retard...
So you'd basically loose the benefits in the upper rpms.
The other benefit is that in high vacuum situation like highway driving it can retard
the cam slightly (along with fuel, timing) to lower the vacuum reversion happening
in the intake manifold. This results in better MPG at these certain conditions.
I know some of us have really looked into the actual settings via HPTuners and
understand this more than others.
Hence the need to limit the VVT actuation when installing a larger camshaft...
I'm pretty old school, but it is nice that you can have a 400HP+ engine that
idles at 600 rpm , gets good MPG AND pulls like a train to 6500 rpm !!!!
All thanks to very complicated engine management systems that are expensive
and hard to diagnose and work on though

 

[Foggy]

My above dissertation only applies to our Gen IV engines as that's my experience.
Other VVT systems are way more complicated and/or better/ worse than ours

Also to add: many engine systems are controlled by oil pressure..
That's why it's so important to always use the correct oil weight and type
and also NOT to go by the DIC or the book... Change your oil more regularly..
that's one of the major reasons why DOD/AFM engines have so many problems...
Way cheaper to change your oil more often than pony up $5000 +++ for lifters, cams
and possible a new engine. Preventative maint is soo much cheaper

 

[Noggles]

I might be in the minority here but I can't wait to get rid of the vvt in my truck. I hate how jerky it makes low rpm driving and I find it does nothing to help low end torque. It just seems like a solution in search of a problem to me.

 

[j91z28d1]

I might be in the minority here but I can't wait to get rid of the vvt in my truck. I hate how jerky it makes low rpm driving and I find it does nothing to help low end torque. It just seems like a solution in search of a problem to me.

I've never once felt anything different from my vvt 6.0 and my non vvt ls3.

are you should you're feeling the vvt work?

can anyone else feel theirs? I do have a odd by tranny in the yukon that might be hiding it?

 

[swathdiver]

VVT is designed to move into the parked position if there's a failure.

VVT makes the motors more fuel efficient, the 5.3s picked up a solid mpg over the non-VVT motors. The 6-speed didn't do much of anything to increase fuel efficiency according to Fuelly.

 

[Foggy]

I might be in the minority here but I can't wait to get rid of the vvt in my truck. I hate how jerky it makes low rpm driving and I find it does nothing to help low end torque. It just seems like a solution in search of a problem to me.

Nope.. Have never felt anything in VVT system in many trucks I've driven.. Have never
noticed it in my 6.2 with either camshaft...
You are probably feeling the DOD/AFM and the torque converter if it's totally stock.
I don't think anyone could "feel" VVT even if you tried

 

[donjetman]

can anyone else feel theirs? I do have a odd by tranny in the yukon that might be hiding it?

No
I have 1 LS powered vehicle with VVT, and 2 LS powered vehicles without.
No

 

[j91z28d1]

No
I have 1 LS powered vehicle with VVT, and 2 LS powered vehicles without.
No

yeah, I think foggy is right and he's feeling afm. is so bypassing that is a good idea

 

[donjetman]

I have 1 vehicle w/an afm engine but its been tuned out.

 

[Charlie207]

I might be in the minority here but I can't wait to get rid of the vvt in my truck. I hate how jerky it makes low rpm driving and I find it does nothing to help low end torque. It just seems like a solution in search of a problem to me.

I don't think there is a huge benefit to VVT with a single cam, when a good tune and headers produce 2-3x more usable power.

Or, gaining displacement.

Once the engine starts utilizing separate intake & exhaust cams do variable timing benefits really become evident, which is tricky on an LS.

I can speak with experience about two different OHC V8s, a 32v 4.4L from three different E39 BMWs, and a lovely 32v 5.6L out of a 1st-gen Nissan Armada.

The BMWs were all 6-speed manuals, so it was easy to always be in the right power and, but they could smoke the tires from a dead-stop, and would truly pull like a flaming cat with gasoline dripping down it's back. The revhlimiter would hit quicker than you'd expect.

The VK56 out of the Nissan always felt like it had max grunt at 1000rpm, and the traction control was always blinking when the roads were wet, even at 23x,*** miles. I wish I had the time & space to swap that VK56 into a Frontier 2wd.

I find my LS to be strong and smooth, and very predictable, but it feels like it needs a split-second to unleash its power, whereas the DOHC engines had hair-triggers. I attribute this to all those intake and exhaust cams able to adjust the breathing to the max.

There's only so much phasing available with a single cam, and we've seen how you even lose some of that range when upgrading VVT cams.

 

[j91z28d1]

my experience with ls engines is they are always laggy and I don't really know why. I don't believe it's the single cam.

I don't count anything auto cause they kinda have to be mushy, Lotta things going on in there but I've owned a few ls in manual cars, both cable throttle and fly by wire throttle. none of them had/have vvt or afm, the cable is better, but still not crispy like a old school v8. I have not driven one on a stand alone ecm, they might be good and it's just how gm codes the stuck ecm? but I've driven many different tuned and bone stock ls cars thru the years and all just feel a bit mushy compared to what a old small block chevy or even a old pushrod Ford 5.0. even old carbed v8's are nasty like that when tuned well with decent compression.

all those are single cam in block. so I don't blame a cam, especially a small one for low end.


end of the day they all run the numbers and go faster but I've always found it a bit odd. I have a guy that works in the shop next door that's always got his eye out for a 57 chevy at a good price. so he talks to the restoration shops and stuff. he tells me the market for non ls swapped classics is pretty bad. noticeable differences in how quick they sell and level of interest. I just don't get it. why would you want to cruise around a old classic car with a laggy ls in it. you lose all the character.

blah.

 

[Noggles]

Nope.. Have never felt anything in VVT system in many trucks I've driven.. Have never
noticed it in my 6.2 with either camshaft...
You are probably feeling the DOD/AFM and the torque converter if it's totally stock.
I don't think anyone could "feel" VVT even if you tried

I feel something that changes around 2500ish rpms at part throttle and I know its not dod/afm because this is when I am taking off from a stop and its not the torque converter locking because its not an rpm drop. Plus I think the converter locks during the 2-3 shift and this happens in every gear at the same rpm. It honestly feels like the cam timing change my old 5 cylinder Colorado had with its variable vale timing and also like the Honda vtec engines I have been around. If what I am feeling isn't the vvt then I probably need to look into it further but I am pretty certain it is. My truck is a 5.3 but my dad has a 2013 6.2 Denali and I am curious if I can feel it in his as well so I will go drive it as well.

my experience with ls engines is they are always laggy and I don't really know why. I don't believe it's the single cam.

I don't count anything auto cause they kinda have to be mushy, Lotta things going on in there but I've owned a few ls in manual cars, both cable throttle and fly by wire throttle. none of them had/have vvt or afm, the cable is better, but still not crispy like a old school v8. I have not driven one on a stand alone ecm, they might be good and it's just how gm codes the stuck ecm? but I've driven many different tuned and bone stock ls cars thru the years and all just feel a bit mushy compared to what a old small block chevy or even a old pushrod Ford 5.0. even old carbed v8's are nasty like that when tuned well with decent compression.

all those are single cam in block. so I don't blame a cam, especially a small one for low end.


end of the day they all run the numbers and go faster but I've always found it a bit odd. I have a guy that works in the shop next door that's always got his eye out for a 57 chevy at a good price. so he talks to the restoration shops and stuff. he tells me the market for non ls swapped classics is pretty bad. noticeable differences in how quick they sell and level of interest. I just don't get it. why would you want to cruise around a old classic car with a laggy ls in it. you lose all the character.

blah.

I think what causes this is the weight of everything in the driveline. I put a lighter flywheel in my ls1 trans am and it made a significant difference. Most ls vehicles are auto with a big heavy locking converter and heavy flexplate so there's a lot of mass to turn there. Plus there is a small delay in throttle response because of all the electronics versus a vacuum operated carb that opens and air and fuel goes in.

 

[Marky Dissod]

'Burst knock' dampens throttle response. It is also indirectly responsible for a minor MpG improvement.
With signal throttle, the engine computer delays throttle movements and dampens how quickly the throttle moves.

GM programs VVT to improve MpGs, not to improve throttle response or power,
until after the throttle has BEEN ALLOWED past a certain percentage.
Under that TPS%, VVT is indeed also discouraging enthusiastic driving.
This is another one of those things that can be tuned to improve (or worsen) engine response.

Finally, GM also 'tunes' the 6L80, 8L90, & 10L80 to upshift as early as possible,
and to not downshift unless you've given it enough throttle - I mean
unless the ecm has allowed the throttle to (stay) open wide enough (long enough) to finally allow / command a downshift.

Yes, we are driving very heavy vehicles that have not gotten any lighter,
and it's a VERY bad idea to use a lightweight flexplate in a heavy vehicle with an automatic.

 

[Foggy]

Yup.. Lightweight flywheels/ FlexPlates in our circumstance is a bad idea.
The weight actually helps with low rpm acceleration.
Noggles could still be feeling the torque converter locking and unlocking...
It's a horrible program for anyone who's tuned a 6L80E... I absolutely love
my 6l80E now that I have changed it. Shifts WAY too early and YES it will lock
up the torque converter in every gear....when stock...
Then you add on when the DOD goes in and out.. And the trans goes to a whole
different set of parameters which makes it worse