Question in regards to the main VE table...

[LS1_Dragster]

I have a question or two, if you get your main VE table dialed in using stock injectors and fuel pressure then down the road you install larger injectors and update B4001 injector flow rate accordingly does the main VE table B0101 change in value?

Also, with the Holley fuel injection, the main map's numbers were in relation to the injector on times, so you could always take a number in the MAP and apply a basic formula and you will get the injector ms on time, it also worked the other way if you take the logs and look at the injector times you could figure out the number in the MAP. So what does the numbers in EfiLive stand for?

And lastly, if at WOT you have a value of 115 with stock injectors then install larger ones and update the injector table, does the value of 115 inject more fuel then the stock injectors? Or would it be identical because the injector flow rate was modified?

Lee

[Mr. P.]

I have a question or two, if you get your main VE table dialed in using stock injectors and fuel pressure then down the road you install larger injectors and update B4001 injector flow rate accordingly does the main VE table B0101 change in value?
In theory, no - you are supposed to "re-educate" the PCM as to what kind of injectors are installed in the motor (IFR table, voltage offset tables, etc) and the PCM is supposed to trim the injectors' behavior to suit. Oversimplified example, you raise IFR from 3.5 to 7, you are telling the PCM that you have installed injectors "twice as large" so the PCM will in turn be forced to halve the commanded on-time. In practice swapping injectors will require tweaking of the IFR value(s) and/or retuning the VE table to get it all exactly right; there is a lot more to describing an injector than it's published flow bench value, the electrical characteristics of the injector contribute to it's real dynamic flow and the replacement injectors may flow differently from the originals in real world use. As a parallel, not all 5' 2" blondes are the same, not all 224* cams are the same, not all 60-lb injectors are the same. You should at least verify that your AFRs and fuel trims are still where you expect them to be after an injector swap, you may find a couple areas in your VE table that will desire *slight* tweaking not because the motor suddenly breathes differently but because the wideband sees the injector difference.


Also, with the Holley fuel injection, the main map's numbers were in relation to the injector on times, so you could always take a number in the MAP and apply a basic formula and you will get the injector ms on time, it also worked the other way if you take the logs and look at the injector times you could figure out the number in the MAP. So what does the numbers in EfiLive stand for?
Sorry, not exactly following your question; aftermarket EFI boxes use far simpler formulas than the OEM stuff, that I know. But if you are wanting to know the commanded injector on-time why not just capture those PIDs in your log?



And lastly, if at WOT you have a value of 115 with stock injectors then install larger ones and update the injector table, does the value of 115 inject more fuel then the stock injectors? Or would it be identical because the injector flow rate was modified?
The PCM will command LESS injector on-time; the 115 value in the VE table educates the PCM as to how many grams of air is trapped in the cylinder at that given time (RPM) and place (MAP) - since the amount of air hasn't changed (it's still "115") the amount of required fuel hasn't changed (you didn't change the desired AFR) so the injector "on" window of time must be shorter.

Mr. P.

[LS1_Dragster]

Thanks for the info.

So the cell number 115 represents the amount of air in grams, Holley's numbers represented the amount of fuel in ms.

So if your injector flow tables are wrong then you would have to falsify the air numbers to compensate for it. This would explain why one persons tune wont work for another's engine despite the fact they are very similar. This must be why the factory uses the MAF to equalize the playing field.

So if you increased your injector size 30%, made the changes in the injector flow rate table then one would expect the injector on time to also be reduced 30% with all things being equal and your Main VE MAP should remain the same. If it was indeed not equal and adjustments need to be made to get the proper AFR, would it be better to fine tune the injector flow rates, injector PW voltage or the Main VE tables?

And with all these variables how would a mail order tune ever be correct the first time? If at all......

Lee

[Mr. P.]

So the cell number 115 represents the amount of air in grams.
NO - it is the volumetric efficiency, or the percentage of cylinder volume filled with air. On a 6.0L motor, each cylinder has a volume of 6.0 / 8 = 0.75 litres of air per chamber; a VE of 115% means that the cylinder has 15% more air in it than it's size (!) or .8625 litres. When VE goes over 100%, you are in boost! When the VE is greater than 100%, then the motor is breathing MORE than 6.0L of air! The only way to do this is forced induction, OR ram-air effect from intake manifold tuning. But in MOST cases a high VE number happens because the IFR table is wrong (value too high?) and the wideband/AutoVE process will scale up the VE numbers to pull the AFR back into line - it's all fun with math...



So if your injector flow tables are wrong then you would have to falsify the air numbers to compensate for it. This would explain why one persons tune wont work for another's engine despite the fact they are very similar.
YES - EXACTLY!



This must be why the factory uses the MAF to equalize the playing field.

1/2-correct; this is not why the factory uses a MAF, but the MAF *does* see the 'real' measured airflow into the throttle body, so no matter what a tooner does to the VE table the PCM isn't fooled, until it needs to rely on the VE table (like during throttle transition, idle, puttering around town at low rpm, etc).



So if you increased your injector size 30%, made the changes in the injector flow rate table then one would expect the injector on time to also be reduced 30% with all things being equal and your Main VE MAP should remain the same.
YUP!



If it was indeed not equal and adjustments need to be made to get the proper AFR, would it be better to fine tune the injector flow rates, injector PW voltage or the Main VE tables?

Before I answer, let me preface that I am a software developer so I have strong opinions on this topic; and that answer is, you cannot lie to the computer without causing hell for yourself elsewhere in the system. So in theory, you want to correctly model to the PCM the behavior of the injectors (hardware) you have installed, so yeah you want to measure all the variables of the injectors on a dynamic flow bench and then carry those values into your injector tables in your tune. In practice, there is only ONE aftermarket injector supplier that takes the time to lab test their products and give ALL the values needed by the Delphi PCM. Greg Banish has hammered this topic to death and published a couple very good papers on it. Anyways, in practice since this information is not widely available we just fudge the injector tables as close as we can, and then let the VE table take up the slack; the VE table won't be theoretically correct, but it'll only be off reality a couple percent, it'll be close enough to work well. But the issue with fudging the VE table too far is that the transmission relies on VE values being realistic, if they are skewed way out of line to accomodate piss poor injector table values then you will have a motor that fuels right but has transmission line pressure and shift behavior gremlins as well as (my guess) spark control gremlins too - just more crap you have to debug out of your tune later.

Mr. P.

[Mr. P.]

And with all these variables how would a mail order tune ever be correct the first time? If at all......


ROFL!!! This will bend your mind - "...with all these variables how would a FACTORY tune ever be correct the first time? If at all..." :grin: And THAT is the reason why the factory has developed/installed a MAF, and is actively trying to develop a 100% real-time foolproof measurement-based EFI control system (rather than a calculation-based one); if/when that day comes, hundreds of calibration engineers and aftermarket tuners will immediately be out of a job!

Mr. P. :)

[LS1_Dragster]

Cool, learning a lot today....I see the importance of the MAF to the general public now.

So, if your cell value is over 100 this means the injectors are not delivering enough fuel so I'm having to fool the computer into thinking it's getting more air then it really is. So I would need to increase the injector flow rate at the MAP reading by the percentage the VE cell is off, so if the VE cell reads 115 then would you increase the injector flow rate by 15% and put the VE cell down to 100?? Does the injector flow change in proportion the the VE?

[Mr. P.]

Cool, learning a lot today....I see the importance of the MAF to the general public now.

So, if your cell value is over 100 this means the injectors are not delivering enough fuel so I'm having to fool the computer into thinking it's getting more air then it really is. So I would need to increase the injector flow rate at the MAP reading by the percentage the VE cell is off, so if the VE cell reads 115 then would you increase the injector flow rate by 15% and put the VE cell down to 100?? Does the injector flow change in proportion the the VE?
You got the idea, the numbers you are using aren't exactly spot-on.

Look at a stock VE table from a LS1; notice that the factory has VE values well in excess of 100% in the WOT 4000-RPM area of the table, 104% if I remember right. Think about this a moment - this means that the stock naturally aspirated motor is breathing MORE than it's own size (347 cu. in.) in air at peak torque! Now back 20-years ago, it was accepted that an outstanding engine had VE in the 95% range, and competitive powerplants were in the 98% VE range, if you were an engine builder and could make a circle track engine with 100% VE you were a god, this is a very impressive achievement. The factory LS1 having a VE of 104% means that at WOT at peak torque it's actually making 1psi of BOOST (lol) so how is that happening?? The answer is that the intake manifold uses ram air tuning at that RPM to artificially 'supercharge' the motor around 4100-rpm. So, if your VE table has values in the low 100's around WOT peak torque then yeah I could see that as being a believable mathematical picture of how the engine breathes; but if the whole table is inflated 15% then the reality is more like the motor's breathing has not changed, just that the IFR value is off and the autoVE process magically scales the VE table to compensate and pull the AFR's back in line.

On your dragster you MAY see legitimate VE as high as 115% *if* your headers are scavenging like hell in combination with a good intake manifold ram-effect at WOT torque peak. Remember the VE table's purpose is just to paint a mental picture to the PCM as to the engine's breathing behavior, i.e. how well it is filling the chamber at any given RPM/MAP situation.

Just because you have a VE table value greater than 100% doesn't mean you don't have enough injector; if the VE value is 150% (real or make-believe) the only place you can check to see if there is enough fuel is to read the result on the wideband.

The commanded injector flow is CRITICALLY dependent on the values in the VE, IFR, and AFR tables; there are other 'trim' or correction tables that have effects too but those three are the biggies and most tuners only modify these three tables to affect AFR changes in the engine.

Mr. P.

[Mr. P.]

Let me break it down like this -

1 - calculate how much air is in the engine.
2 - look-up what AFR is desired, from this calculate exactly how much fuel must be injected.
3 - look-up the injector table values, and calculate how long to hold the injectors open.

Wash, rinse, repeat. Collect prize money. :D

Mr. P.

[LS1_Dragster]

OK thanks.

The reason why I ask is I have my 3 cars running like a top but when I share the tun files they don't work very well for the recipient and I'm trying to get an understanding as to why.

I had the Holley Commander 950 on 2 identical ZZ502's in my camaro and chevelle and when all was said and done they had two different tunes and neither car would run well with the other cars tune. Honestly the only difference was the model number on the headers but they were the same size, spec and brand. It never made much sense then and I'm trying to figure it out now with the GM computers.

I noticed on my 97 Yukon the factory VE at idle was around 74 and at WOT it was 94, doesn't seem like a lot of difference. Yet when I did the 0411 computer upgrade and got it dialed in idle is 66 and WOT is 120, all tuned with my wide band and it runs better then it ever did. I do have a cam and headers but I cant see why there would be such a huge difference in VE. The factory MAF must of reeled it in and made the appropriate corrections!

Lee

[joecar]

In tunetool set your VE units to the technical units g*K/kPa... and from now on view the VE table like this and not as % of cylinder fill...

{
Might as well be all-the-way technical and set fueling units to EQ ("Equivalence Ratio")...

EQ = 1/Lambda = AFRstoich/AFR = FAR/FARstoich

EQ < 1.00 is leaner than stoichiometric
EQ = 1.00 is stoichiometric (regardless of the fuel type)
EQ > 1.00 is richer than stoichiometric

It's easier to use EQ than AFR in technical discussion...

B3601 contains the value for AFRstoich.
}

I have no internal knowledge of the PCM... the following is all based on mine and other peoples observations and experiments (credit to all who have contributed).

From the VE technical units you can see that the VE table provides cylinder airmass "normalized" for temperature and pressure... the PCM uses this and pressure/temperature to compute straight cylinder airmass...

the MAF sensor reports airmass flowrate... the PCM uses this and RPM to compute straight cylinder airmass...

so in both modes (VE or MAF) you end up with cylinder airmass [g]...

then the PCM determines what the commanded EQ should be:
- in CL it commands EQ 1.00 (and trims to this using the NBO2 sensors),
- in OL it commands the EQ specified in the OL fuel table;
- if PE or any protection mode enables, it commands the richest EQ of the enabled tables;

So now, from airmass, commanded EQ and AFRstoich (B3601), the PCM calculates the fuelmass required to deliver the commanded EQ:

AFR = AFRstoich/EQ = airmass/fuelmass

so: fuelmass = airmass/AFR = airmass/(AFRstoich/EQ) = airmass*EQ/AFRstoich

{
also: the PCM uses the airmass to lookup/calculate engine load, ignition timing, engine torque output, and auto trans "torque signal" pressure.
}

So now the PCM knows the fuelmass required to deliver commanded EQ... so now it looks up the IFR table using MAP (in the form of MANVAC = BARO - MAP) to obtain a fuelmass flowrate for the current MAP...

From this fuelmass flowrate the PCM computes the amount of time the injector should be opened to deliver the fuelmass required... the PCM also uses the other injector tables to calculate how much fuel is flowing during the injector on ramp and off ramp, and uses these values to modify the on time such that the total delivered fuel matches the calculated required fuelmass...

So if the VE table and/or MAF table are correct, and if the IFR and other injector tables are correct, then the measured EQ (or AFR or Lambda) will always (pretty much) equal commanded (i.e. BEN is said to be 1.00)...

If any one of those are fudged then you can maybe get BEN 1.00 for some operating conditions, but BEN will deviate from 1.00 for pretty much all other operating conditions.

When you change injectors, if you're able to provide all the correct table values for all the injector tables, then you most likely do not have to edit the VE table.

{
Also note this:
Whether using VE or MAF, the PCM still has to lookup a table and do some computations to obtain airmass...

VE: table is MAPxRPM; PCM looks up table and uses MAP and temperature to compute airmass;
MAF: table is 1xMAFFREQ; PCM looks up table and uses RPM and maybe temperature to compute airmass;

The MAF table has finer precision since it has more cells...
The VE table has coarser precision...
(the PCM interpolates in between cells)...

but if the VE table is accurate, then weather/altitude changes pretty much won't affect the computed airmass... the PCM uses absolute pressure and the ideal gas law to compute airmass... various people have found this true.
}

The powertrain (engine and transmission) should run equally well from the VE and from the MAF, it all depends on how accurate those tables are.

Also, identical powertrains will have variations between them.

:)

[5.7ute]

Great post Joe. :cheers: Very informative.

[ScarabEpic22]

Wish my P10 could display VE as anything but %...set it to g*K/kpa and reopened the file, still got %. This is making Auto VE a royal PITA, plus the fact the column labels are load % and we still dont have a valid Load PID to figure out when the load is appropriate. Just a little frustrating to get it dialed in properly is all.

But it does help me understand the VVE table in my E67...