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Still getting the hang of this Gen IV stuff, had a question on VE tuning with a variable cam. Was wondering if you have to go through the process on the VVE table for each cam degree. For example......Do i force the cam angle to '0', log my error in the VVE, adjust the VVE, and then repeat it for 1 degree, 2 degree, etc..... to the max cam degree angle it will see?
Doesn't look like anybody has responded to this yet...... I am not a tuning guru and have not read specific instructions for VVE but for the last few days I have been using it on a 2007 5.3 and a 2009 6.0 with fantastic results. I logged and filled the table pretty much the same as VE tuning a GEN 3.... and ended up with fuel trims in the 0 to -3 range. Very worth it!
First, are you planning to run speed density to redline or to factory setting of 4000 or to 2000?
Second, do you retard your cam under 3000 or 4000 or 2000? If so, why?
I would think you want full advance in low rpm and the maf is used at high rpm, so why tune ve with cam retard?
As far as cam angle I only filled in the table at 0 degrees and ended up with trims between 0 and -3 so it does not look to me like it would be helpful. I might be wrong though.
Yes, theoretically you would need to collect several Virtual VE tables worth of data, each at a different fixed cam angle. But then you also need to write a tool to do the coefficient regression for VVE vs cam angle that isn't part of the HPT (or EFILive) package. It CAN be done, but it's not currently commercially available.
Sorry it took me so long to respond to everyone, its been a long 2 months, luckily i've finally made it back to this project. Thanks for the replies and insights thus far.
- I plan on leaving the RPM to MAF/SD relationship the same, so anything below 4000 rpm will be left as SD.
- The advance is all stock as i'm not comfortable playing with these yet, i haven't invested enough reading and understanding to do so yet.
- I've noticed there is as much as 25 degrees advance, and so according to the last response, i would need to collect 26 (counting 0) tables of VVE error to do this correctly? Or get a few tables of VVE error and then be able to use a tool that regresses (i'm guessing its a prediction/calculation VS cam angles) the other tables that you didn't collect info for?
- To get by for now, i'll probably just collect the error for 0 cam angle, drive it for a bit to see if the trims get out of control through the other angles, or just set the 3 baro tables to 0 across the board.
You might be OK with just the 0degree VVE tuning. If the cam does not start to retard until past 4000 anyway. Thanks to Higgs for pointing this out.
Bare with me here as i'm still learning what the variable cam values are and what they mean. I did take notice of Higg's comment about retard below 4000, i've attached a screen shot of the low baro cam table. The other 2 baro tables are quite similar. This is the stock values in all 3 tables. So is 0 degrees the base, positive value is advance and negative value is retard? Does a degree in this table even equal to an actual degree in cam change, or is it a different angle relationship?
Attachment 63653
Well our old days understanding was that advancing the cam helps at low RPM (especially if we should have bought a much smaller cam) and retarding it helps at high RPM (small cams included). So the way I understand it (during a full throttle pull) Chevy pretty much keeps the cam straight up until about 3800 when they start retarding it (+numbers).
BUT...after looking at your table I went back and looked at a few GEN4s that I have tuned recently and they also show this cam retard in the low/mid load range. That must mean that there are some low/mid range gains to be had by LOTS of WORK. One option I guess would be to log SD runs with the cam locked at various degrees of retard. I would think that one at 1, another at 3, then 5, 10, 15, 20 might give you enough info to figure out the trends and get pretty good results. The other option would be to do your SD (VE) tuning at 0 until it is really accurate then apply all of the same correction factors to the rest of the tables....but I doubt that would be very accurate.
At any rate...this might be worth while. It kinda depends how much you are having to change your VVE tables at 0. If at 0 they don't need much work I would guess that there won't be much to gain by tuning 24 more VVE tables...or visa versa.
Thanks for not only a response, but a great explanation to why. As i've thought about it more and as you just mentioned, collecting fuel error at separate cam degrees and then interpolating them would probably be my most painless and somewhat dialed in way to do it. I already collected data this morning at what i thought was 0?, till i noticed the Minimum intake/exhaust table that had 2? in it. I guess only Idle is the only time its 0?. Either way i'm seeing about 2-3% lean across the board and then a decent "clump" of 6% stuff below 1600 rpm and between 20-60kpa.
After looking at more GEN4 tunes I see that 1 or 2 degrees of retard is common up to 3800 then they gradually roll it up to 12 or so (plus that area in the low/mid load range). It is obvious why they would retard past 3800 but I don't have a clue why they would retard all of the way through. I have a great client who had name brand "plug-in" tuners so quite a while back I copied a number of them to learn from (even though they were way to aggressive for our gas). At least I could hope that those generic tunes were developed on a dyno and I could learn from their trends. Last night I looked at each of their cam tables. What I saw was interesting....same thing on all of them...they just took one degree out of the factory tables all of the way across. I could easily agree with getting rid of the 1 or 2 degrees up to 3800 but I would expect an increase past 3800 no a decrease.
So maybe all this means nothing... Maybe they actually suck... but...seeing this gives me an idea. Next time I get one of this client's trucks for a day I will get rid of the 1-2 degrees of retard under 3800 and see if it increases KR, affects mixture, makes more power, etc. It might be gainful to get rid of all of the cam retard under 3800. I want to dig into this and get the most for my clients. I better do a bunch of reading rather than asking the same questions others already have answered. Maybe this is part of GM's strategy that allowed them to get rid of EGR. This is getting interesting.
OK. Here goes...It appears to me as though...
Cam park position (0 on the VVT table) is 8.5 degrees of camshaft advance (17 degrees crankshaft) and I think the table is in crankshaft degrees.
So on the LY6 6.0 most of the table up to 3800 (0) the cam is advanced 17 degrees and at 3800 the advance decreases gradually to 8 degrees (9 on the table). It seems pretty strange to keep such a small cam advanced all of the way to redline...so I would doubt that the table is in crankshaft degrees...except for the low/mid load range retard which reaches as much as 8 degrees of retard (25 on the table). Maybe the cam is ground with some retard but I doubt it as it does actually reach 8 degrees of retard in the middle of the low/mid load range .28-32 g. Cylairmass.
After a bit of reading it is clear that this low/mid load range cam retard reduces cranking losses for increased fuel economy. While this does not affect full throttle power it does continue up to .52 g. Cylairmass.....thus the many complaints about the lack of throttle response as the program hurries you into 6th gear. I am no longer inclined to get rid of this region completely but there could be real improvements in response from getting rid of it above .44 or .48 g. etc, etc, etc.
My guess is that there is more to gain on top by going into real cam retard up there rather than just reduced advance. I am sure there are guys on here that tune on a dyno and have delved into this. For me it is just theory for now...
Above I referred to an LY6 6.0. After looking at the VVT tables for a recent L92 6.2 I see that GM takes the retardation 3 degrees further on the upper end (ending up at 5 advanced (12 on the table)). GM also uses the retard function (should call it reduced advance) over a larger range of the low/mid load range (up to .56 g cyl) and excluding the low/mid load retard they smoothly reduce advance starting from idle and all of the way to redline (ending up 5 advanced). And I would have to say that it accelerates much more smoothly through the range than the LY6 that comes on MUCH stronger at 4000...Hmmm. Me likes the L92 strategy much better. You might just have a look at the cam related info on a Yukon Denali a similar year to your motor... I really think it will be worth it to try to apply the system differently.
Cheers,
Jeff
positive numbers are retard off full advance (0).
all that retard at low RPM is for emissions. zero it all out, let the cam retard at higher RPMs like it does.
Higgs/IARLLC, thanks to both of you for helping me out with this. Was hoping you guys could help me know where LS's generally have their cams degree'd in relation to piston location. I had always thought on older SBC's the intake valve would go close just after the Bottom Dead Center of the piston stroke. Retarding the cam would close the valve sooner to get full compression on a full cylinder rather than pushing some of the air out of the cylinder and compressing whats left, like on a stock setup.
-Does my memory serve me right in that regard?
-Did LS architecture continue that typical scenerio?
-In a stock LS cam, is the advance already ground into it that has the valve closed right at BDC for full compression and max TQ?
I know those are vague and general cam questions, but i figure its the best way to ask what the cam degree'ing on the fly is doing and in what direction without using a ton of words.
Don't look too far into it with the stock cam, it varies in each application. Just know that 0 is advanced and numbers off that are retard. Advance good for low end torque, retard good for high end HP. Set it up how you want.
Thanks Higgs!
For what its worth to anyone who may find this thread later........ i just finished smoothing out and calculating the coefficients to the VE table @ 0 degrees for the last time. While watching the 3D VE model, I then increased the cam angle to 1 degree, expecting to see a bunch of changes that would look somewhat like the original 0 degree table. Annnnddddd...........there was a smooth movement, but not like i expected, rather it was a smooth progression/regression in every direction. Where i expected to see 2 totally different 3D models, i saw what appeared to be a calculated change from one table (degree) to the next. And as i increased the angle to 20 degrees, it evenly calculated (changed) across each model in a progressing appearance based from the new 0 degree table. It would appear that changing the 0 degree VVE table is enough (rather than all 0 - 20 tables), assuming the predictive calculations for the other cam angles are correct. Is seems automatic to me, but i'm still fresh at the VVE stuff and am sure i'm missing something.
I have not been able to get a grasp on the virtual VE, but have been trying to understand the numbers in relation to cylinder pressure. Im probably going to try a running compression test and move the cam through the different states on our Ly6 here and see what the compression numbers do. Not sure if it will work, but if im thinking correctly, the old rodders method of camshaft adjustment for atmoshphereic changes by running a cranking compression test with no plugs in it and the throttle pinned open and advancing or retarding the cam to get the highest numbers across all the cylinders. I mean with efi and the plenum in the intake, the running compression test should at least show a trend. I didnt think to look during my logs but as the cam advances and retards,does the ignition timing change at the various rpm and load points to "follow the cam" as well?
Forgive me if it seems like a run on im very tired right right now.
chris
look in your spark tables, there is a VVT spark modifierQuote:
Originally Posted by Rocko350