Many people who are new to tuning the PCM of their car for performance has been lead to believe that the VE tables MUST be changed to get a proper tune.

As they say the more a lie is marketed the more it becomes true.

This causes hugh problems for people learning how to tune their car and are further confused by the vendors who make tuner products claiming you MUST use their product because other brands cannot do VE tuning.

If you stop and think about this whole subject and learn up on how OBD-II powertrains function then you know the VE function was a left over from the old days when powertrains did NOT have a MAF and went by the MAP values and then used statice values in VE tables as what MAYBE the amount of airmass volume was getting into a cylinder.
VE todays purpose is used when engine is started because the MAF is not flowing airmass and is used as a backup system if the MAF was to fail.
Its also used when coming off a lift of gas pedal and is only used when engine is less then 4,000 RPMs.

This means then the VE values are NOT what the engine functions from for most engine conditions.
Since its totally ignored above the 4,000 RPMs then it clearly has no effects on power enrichment or WOT.

So lets do a testcase. We used our 1999 LS1 Corvette which is stroked to 372 CI ( 6.1 Liter) thus cylinder volume is different then stock, it also uses the 2001 and newer intake manifold, uses the larger 85 mm Z06 MAF, has headers and the heads are ported along with a 3rd party CAM using 40 lb/hr injectors.

Now with all those changes and the STOCK VE table values still being used you then have to assume if the HYPE of VE tuning is true then this car should run like crap.

Using the Ease scanner which collects 40 frames a second of PCM data we did a daily driver test run collecting over 40,000 PCM cycles to assure we had a fair look at most engine conditions of what the airflow was versus what the statice VE table values are.
Keep in mind this was done in 40 degree winter weather, the engine compression is 11.3:1 and elevation is around 4,000 feet above sealevel ( which also would impact airmass)

This testrun collected over 33 meg bytes of PCM data !

Results :



As we see the LTFTs are perfect around zero, so are the STFTs, zero knock or misfire and O2s reporting for part throttle just under 0.500 mVolts which is just about 14.1 AFR ( recall the 4,000 feet)

Being there was almost no WOT in this testrun the corrected HP was still 465 and still saw a maximum of 45 lbs/min airflow so if the VE myth was true then this powertrain should be reporting poor performance and OBD-II values
BUT its not !

Now if we let the PCM and OBD II scanner show the facts we see below 3 tables

Bottom is the GM static VE table values
Top table is the reported air volume to cylinders and center table computes by percent the difference in what was in realworld airmass verus the stock VE values. Positive percent values is more airmass then the VE tables values and of course negative values means less air was taken into cylinders then the VE table values.

We can see in some cases a hugh percentage differences thus if in fact the VE tables were so important to engine functioning properly then the car performance and even how well if functioned overall would be quite bad, but its not because in the end its exactly what GM states that VE function is NOT used for most engine conditions and thus blowing your brains out trying to tune for a VE driven engine is a total waste of time in most cases.

Here we found what the PCM reported was the true air volume, compared to the static VE table values, computed the difference in percent and then changed the VE table values with what the true air volume was and flashed a tune into the Rebel
The values in the pink row is the new percent difference between VE table and reported true air volume so as seen within only 2 percent difference now

After 2 days of PCM relearn is a testrun with at least 35,000 PCM recorded cycles of data and the computed true airflow and then a difference to the new VE table values.
Keep in mind values below 25 KPA MAP are from lifting on gas pedal thus PCM is reducing or turning off injector flow and that the PCM will not even use the VE tables above 4,000 RPMs

Here we have a compare of before and after the VE table values were changed within a PCM tune.

As we thought there is ZERO difference in performance, part throttle or idle conditions
We did feel (as expected) some surging during decel.

Both testruns were using same road, same weather, same drivestyle and end results is :

TOTAL waste of time, this again proves the PCM does just fine adjusting to all these engine changes and using the MAF to proper function with those engine mods.

Before VE tune on left, Tuned VE on right

If we remove all PCM cycles where engine was in full decel ( and PCM turning off injector flow) and above 4,000 RPMs ( since predicted airflow is only used below that for a C5) we see then the VE operating range is small as seen below and what is interesting is I see people tuning the whole table even though we know much of it will not be used as a backup when MAF is functional

Are there situations where VE tuning makes sense?

Are there situations where run a SD tune is better than using the MAF?

The MAF not only is faster, but has a larger, finer resolution operating window but also handles weather issues and its output is much faster then if only relying on what SD does using the MAP sensor.

Since VE is used for startup and if using a custom CAM that has lost low end vaccum then that is where VE needs a tweak but as the results show even with many engine changes and increased cylinder volume the PCM still did just fine adjusting with what other sensors reported.

SD would be considered IF a supercharger or turbo is used with higher boost levels where the airmass is way beyond the bounds of the PCM tables such as timing tables that need to know the grms per cylinder to know how much timing to use.

Incorrect VE changes can cause surging since its other use is on decel or anytime the PCM would not used MAF either if there is no airflow such as startup or when butterfly of TB is closing.

VE tuning is a lot of work, you cannot go for a couple mile drive and do PCM scanner recording because to do this right you have to have good averages and hit most of all those points in the VE table matrix. Hitting matrix cell just a few times and the average value seen with scanner would not be correct.

Even once VE tuning is done as seen in results when weather was about the same but drive style a bit different the total averages reported were different so VE tuning is a moving target and simple weather changes can require constant VE table changes required so in the end let the MAF do its job and the end results using MAF are just fine.

I went through this test effort because cyberspace has allowed this myth that a good tune is only via VE is so out of hand that many cars I tune lately that were tuned before by some hacker using VE the engines run like crap and thus there needs to be information for MAF based to equal the playing field on how to tune.

My gut feeling is this got out of hand by

1. those who were tuning OBD-I cars, had no experience with a MAF and thus just decide to tune OBD-II like OBD-I

2. People outside of the USA who careless about American EPA smog rules and engine functions for them.

3. Sly marketing hype by tuner product vendors ( 2 of them sell VE tuning methods, 4 others do not) claiming using their can do VE and competing tuner products cannot ( which is BS)

4. Hackers who call themselves pro tuners claiming have them do your tune becuase they do VE tuning and competing tuners do not

5. Guy who just tuned his own car and now claims to be a cyberspace god and knows it all.

JR

Do the C5R and C6R use a MAF for their racing applications or do they use a proprietry system.

If they find a MAF useful, that should help a lot of misguided souls looking to get their car tuned.

Gordon yes they do for most of the racing GM does requires car to function as one on the street.

Its useless though for you tell people that even the 500 HP new Z06 has a MAF and they still rant that VE/SD is best.
Stupid thing is many yank MAF, tune VE and put MAF back on,
WHY because the PCM uses MAF for many functions including the drive by wire but a lot of this stupid shit comes from the Fbody forums which does not have DBW and has no clue how different the Corvette is with its electronics.

If what they claim was true then my '99 should be running like crap and why I used it in this testing to prove it made ZERO performance gains tuning VE.

OK end of the testing, another 2 days have gone by since last test so PCM is fully relearned after the VE tune was installed

Results of today, exact same performance expected from a mostly cruise drive in same weather as 1st testcase, so NO gains from VE tuned.



If we compare the fuel trims and MAP before VE tuned we see what should be. cells 1 and 21 are decels and should be lean because PCM to conserve fuel will reduce injector flow while there still is airflow



Now look what happens when matching VE table values to the real airflow and now we see cell 21 is super rich when it should be lean



In all testcases VE tuned was a negative and trusting PCM to make use of the MAF is the best path for good running and performing powertrain