I hate that 2-3 shift with a passion because of how much the rpms drop with the lockup. When the trans is cold and the converter isn't locking yet, that shift spread is great. Also, I forgot to mention earlier that I have a dod disabler thing plugged in for now until I do the proper delete and tune hopefully next year.
Understading VVT
- Thread starter donjetman
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I hate that 2-3 shift with a passion because of how much the rpms drop with the lockup. When the trans is cold and the converter isn't locking yet, that shift spread is great. Also, I forgot to mention earlier that I have a dod disabler thing plugged in for now until I do the proper delete and tune hopefully next year.
The "tune" is worth it's weight in gold.. As far as transmission behavior... You'll get
rid of all the lock up in gears 1-3 (some do 4th too, I don't). Then you can get rid of the
unnecessary clutch slippage in 4th - 6th gears ... If it wasn't such a PITA I'd
do a 6 speed in my older pickup (4l80E w 650 HP) and try it in my MontCarlo SS as
I've really grown to like the 6 speed !!!!
Yeah I am really looking forward to how much better that will make the truck drive plus the extra power from the tune and the bigger cam.
As far as the swap, have you looked into Holley EFI? They now have controllers for the 6 speed autos..
The nice thing about vvt is it gives you options to tune a camshaft to an engine/vehicle, that you don't have with a static cam. You are not only advancing the cam for more torque, then retarding it as rpms increase for more power, you can actually build the cam so that it only works properly in certain positions for a certain applicetion. There is a much bigger difference in average power with a properly designed vvt cam, than there is from taking a normal cam, and advancing and retarding it.
I can absolutely destroy the entire power and torque curve of a stock vvt engine by flipping the normally advanced lower rpm cam position to full restarded, then switching the cam position over to fully advanced by peak power rpm. Much much more so than you ever could by advancing and retarding a standard camshaft.
Just like many other things in history, when something is new, lots of people think the old way is better. I personally love running vvt stuff. The only time I don't use it is when a vehicle has no problem making enough power down low. Lightweight cars like corvettes, vehicles with screw chargers, big strokers (though there is even a place for vvt in a big stroker if it's going in a heavy truck.)
I can absolutely destroy the entire power and torque curve of a stock vvt engine by flipping the normally advanced lower rpm cam position to full restarded, then switching the cam position over to fully advanced by peak power rpm. Much much more so than you ever could by advancing and retarding a standard camshaft.
Just like many other things in history, when something is new, lots of people think the old way is better. I personally love running vvt stuff. The only time I don't use it is when a vehicle has no problem making enough power down low. Lightweight cars like corvettes, vehicles with screw chargers, big strokers (though there is even a place for vvt in a big stroker if it's going in a heavy truck.)
I think you're feeling something else. The VVT system is seamless even in my cammed 6.2L.
Charlie207
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Probably the DoD operating on/off.
swathdiver
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Traditional small block chevrolet engines had peak torque in the 2000 rpm range. Our LS engines are high revving like a European car with their peak torque in the 4000 rpm range. Could this dampen throttle response?
I have seen carbureted LS engines that revved like a SBC.
My 5.3 used to lag off the line at WOT at around where the converter flashed to. It had 3.42 gears then. Now it has 3.73 gears and does not lag anymore at WOT from idle. It just revs fast and faster until it shifts.
From my old racing days, I suspect a free flowing exhaust and maybe a better air intake system would allow the motor to rev more freely as well off idle.
I have seen carbureted LS engines that revved like a SBC.
My 5.3 used to lag off the line at WOT at around where the converter flashed to. It had 3.42 gears then. Now it has 3.73 gears and does not lag anymore at WOT from idle. It just revs fast and faster until it shifts.
From my old racing days, I suspect a free flowing exhaust and maybe a better air intake system would allow the motor to rev more freely as well off idle.
Also keep in mind that vehicles from the time when things were carbed, weighed waaaaay less. A newer camaro has no problem pulling down low at around 4 thousand pounds. A silverado that came stock with a carb, weighed 4 thousand pounds or less. Add an extra 1700 pounds to anything, and it gets sluggish down low, even while adding power. That's a ton of weight, almost 2 seconds in the quarter mile based on weight alone. Just imagine a 1987 c10 leaving the line with 1700 pounds in the box.
There are also issues with the stock tune that keep from giving proper power off the line and down low on truck and suv applications. Do a carb conversion and those issues are deleted. A 6.2 in a denali with a tune will jump hard off the line.
Marky Dissod
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If the peak torque is @ 4000RpM, but it makes over 80% of peak torque by 1000RpM, it's fine.
Obsessing over peak numbers is misleading, since most engines spend over 90% of their lives under 2500RpM.
It'd be far more useful to know how much torque the engine makes between 1000RpM & 3000RpM, where it lives.
Biggest things that dampen throttle response are:
lack of displacement - GM replaced Vortec 5.7L with 5.3L, remember? (shrinking the bore tends to move the torque peak higher up the RpM range)
burst knock - this is in the tune, it changes spark timing more slowly than necessary specifically to dampen throttle response ... (there's other stuff of course ...)
87 octane - throttle response & MpG (efficiency per combustion event) improve with 91 or 93 octane, if both sparks tables are written for higher octane
axle gearing - before the 8L90, every vehicle GM sold with a V8 was undergeared at the axle(s).
Most GMT800 & GMT900 with 4L60E should have had 4.10 axles instead of 3.73 or 3.42 or 3.23.
Most GMT900 & GMTK2 with 6L80E should have had 3.73 axles instead of 3.42 or 3.23 or 3.08.
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I remembered that I pulled my stock tune file out with HP Tuners so I opened it up and if I’m understanding correctly the cam timing is set to operate in the 800-3400 rpm range with most of the change happening right around the 2500rpm range.
Now this is with me having almost no experience with vvt tables in hp tuners but based on a thread on their forum I believe this is correct.
mikez71
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Looks very active in the daily driver rpm's to me, but I don't know anything about it ...
Below is the high baro 94kpa map, with mid(84kpa) and low(75kpa) having less effect at higher airflows.
(Low baro map does not affect anything over .36g cylinder airmass until over 3800 rpms, and maxes out at 20 degrees)
Being near sea level, my baro reading is 103kpa. Looking at my logs, I can hit .60g cyl airmass as low as 2000rpms at 50% throttle... In which case the VVT should be inactive...? (until 4000rpms)
Below is the high baro 94kpa map, with mid(84kpa) and low(75kpa) having less effect at higher airflows.
(Low baro map does not affect anything over .36g cylinder airmass until over 3800 rpms, and maxes out at 20 degrees)
Being near sea level, my baro reading is 103kpa. Looking at my logs, I can hit .60g cyl airmass as low as 2000rpms at 50% throttle... In which case the VVT should be inactive...? (until 4000rpms)
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Depends how you think of "inactive." The number 0 means the cam is fully advanced. The camshaft is designed to make maximum cylinder pressure from idle to peak torque at full throttle, then once it crosses that threshold (4 thousand rpms,) it starts retarding the cam because it is now changing over from trying to maximize engine torque, to trying to maximize engine hp.
The full throttle values are straight forward, have a look at your spark tables in the spark correction area under the vvt spark tables. You will see a ton of vvt based spark adjustments to go with those big part throttle vvt adjustments for fuel economy reasons. Just like you can run higher ignition timing for light loads to increase engine power, and thus increase part throttle efficiency, they are also running the cam super retarded in conjunction with piling on additional vvt cam timing.
The full throttle values are straight forward, have a look at your spark tables in the spark correction area under the vvt spark tables. You will see a ton of vvt based spark adjustments to go with those big part throttle vvt adjustments for fuel economy reasons. Just like you can run higher ignition timing for light loads to increase engine power, and thus increase part throttle efficiency, they are also running the cam super retarded in conjunction with piling on additional vvt cam timing.
mikez71
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I think the table shown would be the one I am using, being near sea level.
I say inactive because I heard the cam is fully advanced at rest. Was a little surprised that I would be out of it by 2000 rpms with just light driving. (I think) I'll try and log cam phase to verify...
But it's always retarding above 4k rpms, so I guess it should always help up top? Would you lose peak HP disabling VVT? (with a stock vvt cam)
Depends how you look at it. Are you inactive if you are pushing against a wall that isn't moving and you aren't moving?
The most important thing to keep in mind is that the cam is designed as a vvt cam first, it isn't a normal cam that is being moved around. Take for example the reason why the tune is purposefully killing cylinder pressure at light throttle by retarding the cam. The cam is designed to make as much cylinder pressure down low as possible at higher loads and full throttle to make more torque, thus helping a heavy vehicle to move easier down low. When you have that same extra cylinder pressure in lower load situations where you don't require the extra torque, you need to retard the ignition timing in order to keep the engine out of knock. To get around that, you retard the cam so the cylinder pressure drops, then you ram timing into it to maximize the efficiency of the engine.
When you see that the cam is "inactive" you are basically seeing the true nature of the design of the cam. When you see the numbers, you are seeing the adjustments used to make that base design as efficient as possible in the spots it was not designed to be it's best. They aren't using the numbers to make the cams performance, they are using the numbers to make the cam less ****** where it isn't optimized in the base design of the cam.
The most important thing to keep in mind is that the cam is designed as a vvt cam first, it isn't a normal cam that is being moved around. Take for example the reason why the tune is purposefully killing cylinder pressure at light throttle by retarding the cam. The cam is designed to make as much cylinder pressure down low as possible at higher loads and full throttle to make more torque, thus helping a heavy vehicle to move easier down low. When you have that same extra cylinder pressure in lower load situations where you don't require the extra torque, you need to retard the ignition timing in order to keep the engine out of knock. To get around that, you retard the cam so the cylinder pressure drops, then you ram timing into it to maximize the efficiency of the engine.
When you see that the cam is "inactive" you are basically seeing the true nature of the design of the cam. When you see the numbers, you are seeing the adjustments used to make that base design as efficient as possible in the spots it was not designed to be it's best. They aren't using the numbers to make the cams performance, they are using the numbers to make the cam less ****** where it isn't optimized in the base design of the cam.
Marky Dissod
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When is the variable cam timing 'at rest'?
The zeros in the table in this post?
Is there another table that shows when the Variable Cam Timing is or is not in effect?
Hagar, is the word you were looking for
schidty?
Haha, that was the word. The cam is fully advanced anytime you see a 0. It can not possibly go any further advanced than 0, but it is being held at 0 so it's not really at rest. Just semantics i am sure, but it is being forced to stay at fully advanced when it is showing a 0.
You can log the vvt position to know when it is moving off fully advanced, but it's movement comes from meeting certain criteria, not a table itself that activates it. It blends with other tables.
mikez71
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Here are the MAX values driving around.. Was thinking there must be other maps/modifiers..
Averages from the same log below, mostly normal driving with a couple heavier throttle sessions.
(80% throttle at most)
Averages from the same log below, mostly normal driving with a couple heavier throttle sessions.
(80% throttle at most)
You can look at that log of cam position and see in it how the engine works just by the way numbers change vs load and rpm. The points where the numbers are the highest, are the heaviest loaded points under normal light throttle driving, or even could be into a super efficient zone where the intake flow just stacks up better because of the manifold design.If you take data point .20 load at 2,000 rpm, it is the highest cam retard because that would be the point the engine is having a hard time taking timing. If you open up your vvt timing adder table, it will be adding extra timing at that point.As the rpms increase at the same .20 load point, you can see the cam timing starting to advance again. It is advancing again because the load on the engine goes down once the vehicle is getting its kinetic energy up to speed, but also the engine is getting into its efficiency range at that point, so the computer starts telling the cam to advance and bring the cylinder pressure back up.
The computer is basically swapping cylinder pressure and ignition around at different points to make the engine the most efficient it can be. At certain points, it is better to have more cylinder pressure and less timing like at full throttle or heavier load, and sometimes it's better to have less cylinder pressure and more ignition timing for best results, like at max fuel economy light throttle range.
The computer is basically swapping cylinder pressure and ignition around at different points to make the engine the most efficient it can be. At certain points, it is better to have more cylinder pressure and less timing like at full throttle or heavier load, and sometimes it's better to have less cylinder pressure and more ignition timing for best results, like at max fuel economy light throttle range.
Marky Dissod
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Interesting, that there is not ONE table that simply says, 'this is where VVT will always advance, this is where VVT will always retard',
although I'm fairly sure that it can be predicted by RpM & throttle.
(I'm a mid-90s LT1 tuner who genuinely thinks that the vast majority of the increasing complexity of ecm & tcm tuning is akin to when a Dr could say
he had a heart attack which knocked him out and stopped his heart, but we saved him with an injection instead of electrically
but instead says
he suffered a myocardial infarction, during which he suffered a syncope and a near-terminal arrest,
but we cardioverted him chemically instead of defibrillating him)
If 'full advance' = 0, which the ecm has to command,
where is the cam when the VCT either fails, or is simply 'relaxed' because it is momentarily passive / doing nothing?
Is it when the cam is fully retarded, or somewhere in between?
