Freak

thanks for the info Joe

Blackbird

Great thread.

Joe - Your doing zero with PE vs RPM ???

When tuning this way how does it effect part throttle behavior?

I have begun searching for info on how I can best tune for gas mileage ( don't laugh please ) and it's sounding like the VE table may be the place to explore.

In your opinion could I lean out idle/part throttle there for mileage and then basically overcompensate in PE vs RPM for WOT situations to achieve my desired A/F at WOT?

Thanks in advance!

ChrisB

You have a target a/f ratio (say 10:1). So for 10 parts air we need 1 part fuel. We look at the MAF flow rate and it tells us exactly how much air is coming in at any given instant. We know what the fuel flow rate is, so we just need to open the injectors for the appropriate amount of time to enter that fuel.

If you look at a SD (MAP only) car then it does the same thing essentially. From a manifold pressure and RPM value a VE value is determined from a lookup table. This value is then used to determine what percentage of an ideal engine (100% VE) airflow we are actually observing (ideal engine airflow is just based on displacement and rpm). So if an ideal engine flows 600CFM and we are at 50% VE we have a 300CFM flow rate. Then using barometric pressure and temperature that value is converted to massflow. Thus we end up with a massflow rate, just as the MAF meter initially gives us.

Now if the LS1 is actually using the VE table it would probably be as some sort of transient fueling modifier (my guess - if it is causing stumbles, etc. this makes sense). In order to understand and lay out what changes would be appropriate I think the above questions need to be answered - otherwise it is still just guessing!




Where are you seeing a RPM in the MAF table? Are we looking at the same table? The MAF transfer function just maps a frequency to a mass flow rate. If you have the same airflow rate and the same target a/f then you *should* be spraying in the same amount of fuel - remember, changes in effeciency of the engine cause it to pull in less air (why it makes less power) - and the MAF is going to meter this directly. So essentially the VE is factored into the MAF reading by the way it operates. This is why you don't *need* it. (Again, that doesn't mean it isn't used - I am just answering the question you posed).



You can tune a car if you get the MAF dialed in perfectly setting only the target AFR. But the MAF isn't perfect, and the PE table acts as a safety device, as well as an easy way to adapt the same pcm to different combinations.




Nope, look at the PE table - it is an enrichment factor based either on RPM or Temp (depending on which one you look at). Now there is a MAP threshold for activation, but there is also a TPS threshold. It's a RPM based enrichment factor for sure though (or temp).



I agree with this I think - *if* the VE tables are used (which I am still not convinced of, but there seems to be some anecdotal evidence that they are. Again, log files could answer this question easily). If the VE tables are used the only purpose I can see is for transitional fueling changes, again, like an accelerator pump shot. This would explain stumpling/sputtering, and would make some sense since there will be an inertial lag in MAF readings under high transients. But again, that is just supposition.




Look at some of the LT1 Edit list archives, this was gone over extensively. I ran some tests myself on my vehcile - setting the VE, across the board, to "1" made *no* difference in perceived drivability, power on the dyno, or track times (as well as fuel trims and mileage). Next I set all cells to 99, and again, no change on the above factors. I have dynos (Back to back) +-4rwhp to back this up, as well as timeslips and log files.
Try it on your car - if you are using a MAF and not in SD mode then you will see the same things. "perceived drivability" is tricky as a metric because so many other things effect it (as well as the placebo effect) - you reset your fuel trims, the car learns as you drive, etc. That is why I would suggest making a large change so that effects are obvious and quantifiable (loggable). The results were verified by many people on the LT1 Edit mailing list.
But admittedly that doesn't say *anything* for how the LS1 operates, which is why I am curious for someone to run the tests mentioned.





It's good to be carefull, and I agree to an extent, which is why I posed the questions above. But also at the heart of tuning is going to be experimentation. As long as you are sensible with your changes and are good about logging in order to quantify changes you can very easily and safely make changes to see what the effect is - many times this is the only real way to settle debates (Such as this one) - since we don't have access to the source, or a commented dissasembly.

Bink

FWIW - Both Ken Kelly (in the LS1Edit user's guide v1.2 -> VE page 29) and Probst ( in his Corvette EFI book) state that VE is used in Closed loop. Ken says "it is not used in Normal WOT operation, but has an effect on closed loop fuel trim". Mr.Probst states that it ( Volumetric Efficiency) is used in determining the injector base pulsewidth equation.

joel (Bink)

Cal

iTrader: (1)

Also FWIW, I noticed the strong, raw-gas smell I had at idle after my cam install is totally cleaned up now after scaling the 1200 rpm and below VE by 60%. Lost a little driveability though - I think I'll take it back to 80% next and try that.

Bink

Has anyone tried this???? My car is down or I would. Someone, PLEASE?
joel(Bink)

Cal

iTrader: (1)

OK I just tried it: scaled the Main VE from 1600 rpm to 3200 rpm by 200%, all map values, loaded it into the PCM, started EFILive5 and went for a 2 mile ride. I can say this much, it ran so bad a couple of times I thought I was going to have to flash my PCM just so I could drive home! Engine tried to shut down everytime I went into the rpm region then tried to slow down. The log file shows the O2 sensors flatlining during these periods. I also drove the same route and logged with EFILive before changing the table as a baseline.

ChrisB

Could you email me the log files? Thanks for taking the time to try it out!

chris@slowcar.net

(if you could zip it up first I would appreciate it - I'm on a satellite connection right now)

Bink

Thanks Cal!!!! So the O2s went down - I guess it's going open loop to maintain operating function??? Did it throw any codes???
joel(Bink)

Cal

iTrader: (1)

Chris, sure when I go home on my lunch break I'll send them to you. I assume you would want the baseline as well since my normal tune isn't stock either.

joel, no problem, wasn't that much effort to try it, but I was sure glad to get that funky tune back out! I'll have to look again, but I think it stayed in closed loop the whole time even with O2s going off line (other than intial warm-up, of course.) No didn't throw any codes, amazingly enough. The strange thing is I could accelerate right into the test region with no apparent problems, but soon as I let off a little, it started bogging and trying to die out just like it suddenly ran out of gas.

ChrisB

Okay got the files (as well as the VE tables) - thanks! I only had a bit of time to play with it, and though I haven't figured out exactly the manner of the fuel adder based on VE it does definitely bear out a VE effect on fueling.

I found the average pulsewidth and scaled it vs rpm and map (like VE) and rpm and MAF (a fueling analogue). I then subtracted the 200%VE table results from the normal VE table results. In both of those there was a noticable increased, and an average increase also (there was one high point, but even with throwing that out there was an increase).

I then plotted MAF flow vs. rpm and MAP and noticed the MAF was essentially unchanged - so the change in fueling had to be due to something else.

I made a summary of the results with graphs at
http://www.slowcar.net/VEComparo.htm

(apologize for the MS Word generated code - but it sure was convienent).

Some of the graphs are a bit "spikey" because of the lack of data points (they get plotted as 0 by default) - but even with that there was still a definite average and overall increase.

I did this same thing with my LT1 and noticed no statistically relevant change - but here there definitely is.

What I think is the most promising is tht the average pulsewidth increase seems to scale with RPM's (for RPM ranges we have enough data for) - which is *exactly* what a multiplier would have to do.

Now we just need to figure out exactly how the VE is adding fuel (in what manner/form).

(FWIW the values I used are filtered for TPS over 5% - i haven't experimented yet to see if there is a TPS correlation).

Just wanted to say thanks again to Cal for taking the time to perform the tests and send me the data!

I will post the excel file later on - it's about 15 megs and I am on a slow connection, so it will take me awhile to get it up.

Joe Overton

glad I could help some

Cal

iTrader: (1)

Chris, good work on the data reduction! Looks like at this point we know for sure the LS1 VE works different than it did on the LT1 engines and cannot be treated as parameter just for adjusting engine startup behavior. I believe VE has an impact on both steady state fueling and transient fueling changes. Also, I'm pretty sure that VE has an impact on things other than fueling, like spark advance. If we could fully understand how the PCM code is using VE table values it would sure make tuning easier and more accruate.

Cal

iTrader: (1)

Joe, thanks to you and NoGo for your insight into this VE stuff as well!

Bink

lOOKS LIKE kEVIN, jOE AND cHRIS DON'T NEED TO "AGREE TO DISAGREE" ANY MORE"!!-damnit my caps were on, sorry guys.
joel(Bink)

Joe Overton

No problem ,I own a lt1 but I still try to help ls1's even though I'm the black sheep so to speak...

Cal

iTrader: (1)

Well I have one of each (LT1 and LS1) but the LT1 is a '93 with an EPROM based PCM, so I don't tweak that one.

98TAauto

iTrader: (2)

Im another of the LS1's Joe has tweaked in the VE table. No dyno numbers yet cause those really dont mean squat to me. Ill see how she does at the track this year. I do know its was a night and day difference before and after his tune. Top end feels un friggin real now. If some of ya'll saw the timing tables you might pass out HAHAHHAHH j/king Joe

Im trying to learn how he tweaked the VE stuff, but im just a newbie. Im not messing with it unless I know what im doing. But these edits arent gonna change after a week, month, or year like playing with the MAF and PE/RPM tables Like Joe said, those others are just a quick fix(aka bandaid).

Awesome Work Joe

Bink

^^ ^^ ^^
joel(Bink)

Bink

Moderators- could you Guys sticky this for proof of VE use closed loop - in LS1/6??