Need clarification of something for VVT tuning of the LE5

VVT tuning is something that has boggled my mind for quite some time with hptuners and this cobalt ss, but after examining the way the camshaft actuators work I think I finally understand it and I just need some clarification if this is indeed how it actually works. HPtuners gives two 0-25 degree tables in what is presumably crank degrees for low medium and high baro settings for the LE5, but what puzzled me was the direction the cams were going, was the VVT retarding or advancing the cam, this I could not figure out. But to my current understanding with the way the actuators work on the gear, each cam, intake or exhaust, can only move one particular direction on the gear. So for instance with the way it seems to be setup, the exhaust cam gear only retards the exhaust cam 0-25 degrees, and the intake cam gear only advances the intake cam 0-25 degrees. Would this be a correct assessment of how the VVT works? I am basing this off of the design of the gear itself of course and given the fact that there are no negative numbers in the HPtuners adjustment tables indicating that it only moves one direction.

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usually the intake gets retarded and the exhaust gets advanced. at 0 % duty cycle you are at full park (sometimes park position occurs before you get it to 0% duty). Park position is dictated by the vane setup. the larger the minimum distance is between the inside vanes (the inner vanes are attached to the cam) and the outside vanes (attached to the gear as both are shown in your picture) will determine the amount of degrees mechanically allowed by the system. when the inner vanes touch the outer vanes you are at max mechanical travel.

most engine run best in overlap therefore its easier to design a system that controls more overlap event than it does separation event. generally speaking 85%-90% overlap control to 15-10% separation control. with that info 99% of the systems are setup to advance the intake cam you move it towards overlap, and when you retard the exhaust cam you move it towards overlap. reversing these movements gets you less overlap. retarding the intake gets you less overlap (if you exit overlap doing this will gain more separation), and advancing the exhaust does the same (less overlap or more separation).

naturally you would think that air comes in the intake first so when you read the cam card the intake is the first event then exhaust but the real way to read it is exhaust first/overlap or separation event/intake last and ignore the compression cycle unless you are trying to design a cam and want to know where the opening of exhaust and closing of intake leave you for full compression time.

if you look at the cobalt ss lnf/lhu we say park is +10 intake and -6 exhaust. that's because the computer isn't a 0-100% duty cycle chart. these tables are more of a 0 is beginning of overlap and positive values are retard & negative values advance. thats how gm and bosch wrote it. if your motor is non-interference keep shifting the cams until you noticed the cam sensor signal stop moving. now you know where mechanical park and mechanical full apply are in correlation to the tables values. you will have to do the same for the le5 as well. once you know where the stops are you can now tune in the effective range without wasting time outside of the mechanical limits. if your intake and exhaust cam tables are both positive values only then the intake cam will retard as you increase value size and the exhaust will retard as you increase value size.

this should be enough info to get you started. any question's arise just post them here and the forum will answer.

CSSOB

ps: look at a high quality ls cam kit. you will notice due to interference at large duration's and lift the cam kit designer will supply a few pieces of metal. these pieces are small and get inserted between the vanes to limit the mechanical travel allowed in the cam system therefore eliminating the possibility of internal interference between rotating assembly and valve-train components.

courtesy comp cams: http://www.compcams.com/Technical/In.../COMP4-122.pdf

^^^ "exhaust will retard as you increase value size"

I now believe this, as I made a log a few days ago with stock vvt tables and then exhaust advanced 2 in the table and I lost ve airflow. Have not had a chance to lower the numbers in the cam table yet to see if I gain ve airflow.

and sub'd for any info that shows up for the LE5
thanks

with the LNF LHU tables being dual value (+&-) that's how we determined the direction. made a wot pull stock got baseline injector time, ve, maf values and set the trims as locked down as possible.
made a 5-8 value shift and monitored the data. with the drop of ve the trims went negative showing too much fuel was being injected. since all was done was a cam shift that shows a reduction in airflow(less overlap). the maf is there to further confirm the ve input data.
if your boosted you can also watch boost pressure as more overlap tends to flow turbos out dropping the pressure.

retarding an exhaust cam will induce more overlap. like i mentioned don't end up reading the cam cards backwards.

advance means come sooner, we all know this. the events are laid out as follows... exhaust-intake-compression-ignition-exhaust
with that if your heading toward the exhaust event and you advance its timing you just moved it towards the ignition cycle not the intake cycle. (less overlap)

easier to understand now?

it wasn't included but you are on the right track to mapping out the cam system.

+ exht = advance/less overlap

Just wanted to follow up on this a bit since your explanation helped me greatly. I'm having a set of 2.4 VVT cam's made. We measured out the stockers to be 190/170 duration @ .050 and we are going up to something similar to a small comp 2.2 grind, 204/200. I've been evaluating the VVT tables just trying to get an idea in my head how exactly the cams will be transitioning through the RPM range, but there is something that confuses me, why are the VVT tables not smooth progressions throughout the RPM range? You would think you would want it to be a smooth transition from as little overlap as possible down low, to decent overlap up top, but in the mid range the numbers get erratic and are anything but smooth. If you assume a consistent WOT cylinder airmass from a dead standstill, we find VVT going from 1-3-5-2-15-13-12-10-7-5, but then if the cylinder airmass increases just ever slow slightly, we find ourselves 24-24-24-24-22-20-15-10-9-7. This to me seems like the power is going to be all over the place at WOT depending on subtle variations in the cylinder airmass. Any insight into why this is?

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Let me be the first to say that stock tunes are absolutely horrible. I don't know much about the LE5 but I can guarantee you that if done right you'll find a huge gain in performance, DRIVABILITY, and if you choose mpg. Yes tables should be smooth. The more power you produce the smoother things should be and the faster the rotation the smoother it should be. Also included is smaller changes with more power and faster rotation. A lot can be learned from the stock tables so try to understand why they set things up the way they did and also try to figure out why they are also wrong in areas. Sorry this isn't very informative but to be honest it's hard to explain without giving away what to do and that is not my style. I am planning on writing up a better VVT write-up but I deal with the LNF so some things will be different but I think it'll benefit you a lot.

^this

Simplified, what MikeM is saying is:

1) GM stock tables were written by crackheads.
2) Extremely beneficial and important to have your tables as smooth as possible.
3) GM buys good crack.

Let doesn't have as much gain as you think cam shifting would net. I'm a firm believer that factory le5 cams are not a good grind

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Originally Posted by cobaltssoverbooster

Let doesn't have as much gain as you think cam shifting would net. I'm a firm believer that factory le5 cams are not a good grind

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Judging by the factory specs and what ive compared with other VVT 4 cylinder motors id be forced to agree with you here, problem Is I dont know where to start when trying to design new VVT tables. Yes I can get some dyno time but I dont think an hour is going to be enough time to sit there and redesign the entire table, not to mention I have no idea where to even start. lol Even the 2.2 LAP tables are no help there as well, just as wonky. Any suggestions you guys might have would be greatly appreciated. There is virtually nothing out there on the forums for this, seems people just abandon it for a LSJ head rather then trying to take advantage of the VVT.

Most gains will come from forced induction when it comes to VVT I my opinion. I would honestly save this table until last and here is my advice for people. If you want to redesign the while table do chunks at a time. Also notate loads. My car is always below 90% unless WOT do I changed table values around to accommodate that. Also since I'm turbo and I have it spool in a certain range I set my rpm values up around that. Then you can focus on sections. If you want mpg you can work that area then smooth it by hand. Then focus on an adjoining area. For me it'd be turbo spool the. WOT. Also I had to work idle. Everything else you have it smoothly flow into each section. Sometimes you have to lose gains in an area because you want gains in another and if you don't change it then the shift is too drastic and you get knock. Smoothness is key in every table. You'll notice GM doesn't seem to care about smoothness.

You start with whole table at zero. Record effects of almost every cell in trq by using solid state control. Then shift the whole table 20%. Do it again. bump to 40..60..80..and last 100% repeating trq measurements every time. Take all the trq values you got and plot cam shifts that made the most trq in each cell. The graph will be jumpy due to shift range. If you notice the trq values don't make power past a certain shift then cap it off and try shifts in a lower percentage like 10%. After plotted you smooth the entire table and fine tune adjust the rest. Custom cam table complete.

This is why I plan to do another write-up on the subject. What CSSOB said will work there are other things that will provide gains. Its not just values but rather the changes in the values as well from one cell to another. Let us know how it goes since your running the LE5.

The ways I adjust cams are limited to two options which are determined by driving style required. They both require solid state dyno. Adjust cams by trq output only (race applications) and adjust by monitoring fuel flow and trq output (street and combo racing). If you have factory cams you can do what Mike has in store for everyone otherwise new cams require a complete remapping which involves a lot of dyno time and with GM ecotec not being live efi status takes for freaking ever. The ways I talk about aren't the only ways by any means but as questioned by poster, for starting over are the only real way to know you programmed to the correct positions from scratch.

Very good points.

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Originally Posted by cobaltssoverbooster

You start with whole table at zero. Record effects of almost every cell in trq by using solid state control. Then shift the whole table 20%. Do it again. bump to 40..60..80..and last 100% repeating trq measurements every time. Take all the trq values you got and plot cam shifts that made the most trq in each cell. The graph will be jumpy due to shift range. If you notice the trq values don't make power past a certain shift then cap it off and try shifts in a lower percentage like 10%. After plotted you smooth the entire table and fine tune adjust the rest. Custom cam table complete.

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Gonna have to get some dyno time in then to figure this out, i screwed around with it a little bit the other day, just dropped the whole column to 24 degrees even in the low rpm part throttle areas, car felt alot torquier and smoother across the whole power band, but i showed a consistent decrease in fuel requirements across the board in my LTFT's, which probably means i shifted the powerband significantly lower, probably needed more timing as well in the lower rpm areas. So that's something im definitely gonna have to play with but after the new setup is in I think. No sense working with the old cams.

I would still recommend playing with it now and learning everything you can without a dyno. You can still measure performance without a dyno.

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Originally Posted by MikeM173

I would still recommend playing with it now and learning everything you can without a dyno. You can still measure performance without a dyno.

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Like i said, ive done a bit of playing with it, and had some good and bad experiences with it on the street so I have an idea of how its going to pan out. Big thing for me is actually understanding the opening and closing events in relation to the gears moving, that for me is plotting the new cams vs the old ones on a degree wheel and seeing how the VVT effects it. That helps me understand the cam movement alot better. Giving me a general idea of just how much and where to move the cams to get more torque down low and better power up to, rather then just throwing numbers at a chart. The advice in this thread has been invaluable in helping me understand the system.

Just wanted to bump this thread with an update. Me and a friend spent a few hours doing some tuning on the car today because the car felt very flat up top 65+mph @ WOT. It would not pull through 3rd and would die in 4th in the high RPM's. I recently rebuilt the motor and used a LNF exhaust cam with the factory LE5 intake cam. This changes the specs from .415/.395 lift 210/195 @1mm to .415/.405 210/194 and changes the LSA from 130 to 127.5. LNF exhaust cam has a centerline of 120 where the LE5 exhaust cam has a centerline of 125.

After doing alot of maf tuning and dialing in the o2mv @ WOT to around 880-890 we made a +3 degree change to the intake cam high baro table listed above from 5200 to 7200rpm. This seemed to breathe new life into the car. Pulled alot harder in the high RPM's, now granted this is all being done through the butt dyno but what exactly was advantageous of the change we made. By what has been said before I believe what we did was open up the intake cam slightly earlier which I believe should have helped draw in more air at the high RPM's and increased overlap as well by in the opposite direction of the stock LE5 cams since a tighter LSA is already ground into the stock LNF exhaust cam. I need to get to the dyno when I get some extra money and actually use their wideband to see what o2mv is actually optimal for this car at WOT because I wont be installing a permanent wideband until I start looking to boost. Right now we have just been referencing what the LS1tech guys use between 850mv lean and 900mv rich.

Iirc larger numbers equal retard intake cam and advance exhaust cam. Full park is almost always fully advanced intake and fully retarded exhaust.