Tuning for headers

[cmitchell17]

I just ordered some OBX long tube headers for my 2000 5.3

Ive been serching and found some diffrent results, but I concluded that headers are going to add airflow so the VE table will need adjustment for this.

The longtubes will move the narrow band O2 and screw up fueling even more.

Hopefully I can get a WB but not anytime soon.

After I install them I think im going to raise the ve about 6-10% and richen up PE to be safe.

I also heard at high rpms ve dosent really change but only changes some in the low and mid range.

Id imagine that the the NB O2 will be completly worthless indicating the trims becuase their going to be farther from the exhaust ports.

[SOMhaveit]

It should make you run lean, but I didn't see that when I installed headers on my 5.7.

If the guys who spent the time to figure all of this out are correct, above 4000 you are running off the MAF curve, so your VE table has less/no influence over AFR. You also have the PE table and cat protection to keep you from going lean in the higher RPS's. And unless you're running Speed Density, VE is a factor in determining AFR but not the only factor.

With headers, head porting, cam, & high flow exhaust, I actually only ended up about 5-8% higher in some of the VE table values based on AutoVE.

[mr.prick]

you probably won`t notice a difference.
i had someone tune my car and left the VE table stock and set
the PE to 9 AFR
http://smiliesftw.com/x/eek_animated.gif (http://smiliesftw.com)
and i would hit 9 AFR.
this was with a stroker motor, not just headers.

[cmitchell17]

Yeah I guess ill just add a little at first and drop the timing a little and see what happends.

[cmitchell17]

How does you VE table not have any affect on AFR over 4000?

[SOMhaveit]

How does you VE table not have any affect on AFR over 4000?

Well, I guess only GM knows for certain, but from all of the stickies, posts, & blogs I've read, above 4000 in closed loop, you are basically running off the MAF table and PE Table.

Guru's correct me if that's off base.

[5.7ute]

If the maf is enabled it will use the maf exclusively for the fuelling calculation once B0120 is met. The default setting for this table is generally 4000 RPM.
Under this setting if the maf is enabled a hybrid calculation between maf & the VE table is used.

[cmitchell17]

Wait, I might have everything messed up but I always thought the maf and map metered the airflow then made a final value then looked that up in the ve table to see what the volumetric efficiency was then it injected fuel.

So does if it sees a certain maf reading than it dosent even have to look at the ve table it just knows how much fuel it needs by looking at a certain grams/sec?

[dc_justin]

Wait, I might have everything messed up but I always thought the maf and map metered the airflow then made a final value then looked that up in the ve table to see what the volumetric efficiency was then it injected fuel.

So does if it sees a certain maf reading than it dosent even have to look at the ve table it just knows how much fuel it needs by looking at a certain grams/sec?

The VE table is an airflow "lookup" table that the PCM references based on MAP input and RPM. The MAF sends a signal to the PCM (in hz), which it interprets and compares to the MAF calibration table.

When the MAF is enabled and the dynamic airflow threshold has not been passed, the PCM will use a combination of the airflow sensed by the MAF and the airmass calculated from the VE table (via the MAP) and charge temperature (IAT & ECT).

When RPM is above the dynamic airflow threshold and MAF is enabled, then the VE table is completely ignored and the MAF Calibration will be sole airflow reference.

[cmitchell17]

So where is the table that tells the pcm how much fuel it needs for a given grams/sec?

[dc_justin]

So where is the table that tells the pcm how much fuel it needs for a given grams/sec?

There is not one table, there are multiple.

Takes stoich AFR into account and whatever commanded fuel modifiers are in play, ethanol percentage, etc.