Street vs Dyno AFR variances? Also, PE/fuel trim questions..

[Chris81]

How much variance are you guys seeing from the dyno to the street?

I've heard anywhere from the same AFR to .5 to 1 whole point higher on the street/track than the dyno..

I would love to know since alot of people shoot for 12.8 -- 13.0 on the dyno.. but i'm tuning on the street and at the track, right now i'm at 13.0 WOT on the street.

any help/comparsions would be great

Also, any insight as to why my actual is 13.0 but my commanded is 12.5?
My LTFT avgs are between 0 and -2 and the MAF and DYNAIR are VERY close, probably within 1 % or so at WOT.. the car runs great.

One more thing.. just today i'm starting to see positive LTFT's at WOT when before they were ALWAYS 0, i'm assuming its the colder weather.. but is there anything else that can contribute to this?

Thanks!

Chris

[caver]

Mixtures always vary on the road as the engine is very seldom at a steady speed and the pcm is almost always playing catch up.Normally mixture on the road is leaner than on the dyno unless you were doing inertia runs,in that case they should be close.

If your commanded and actual AFR is not the same its because your maf table is'nt set up properly if you are running one. If maffless then your VE table is'nt correct. Try raising the values in your maf table slightly maybe 2% or so.

As soon as you go into open loop your ltft's are inactive so I would'nt worry about it.

[Chris81]

Alright cool

I have a new MAF calibration setup I just haven't tryed it yet, i'll see it that fixes it in the morning.

[ringram]

Im not sure that if your commanded and actual are different its totally the fault of the VE table. Mine is bang on around town, but lean on the motorway.
There are a lot more variables, like IAT and VSS which come into play, especially if you run things like otrcai's.
I think the best you can hope for is to use modifiers to help, afterall thats why they are there in the first place to "modify" the VE so that it matches more closely.
So I wouldnt be too worried about minor variances, have a play with the modifiers.
Ross, Paul or someone with more knowledge may be able to confirm this.
Check out the Custom OS IAT modifier for example.
Perhaps a VSS modifier is also in order?

[caver]

There will always be slight variations.Remember the BEN map is Average mixture. If you monitor the ben factor instead of cell counts you will see it either starts out rich or lean and then assumes more sane numbers as it's averaged out.
You could log yourself to death and never get it spot on everytime. Thats why closed loop is there to keep it pretty constant under different conditions.