This has been hashed before, but since I had some time, I did some live testing for Air Fuel Ratio and I thought I would share my info:

I have 2 MAFs
1- Stock MAF
2- Granatelli MAF

This is live with a wideband O2 reading both left/ right at same time.
Tune is rich for nitrous use.

So I thought I would swap ends from one to another etc...

Test 1- Stock MAF (screened)- BASE TEST-

Stoich-14.7
WOT- 12.6

Test 2- Stock MAF (de-screened)
Stoich-14.7
WOT-12.7

Test 3- Stock MAF (with ported granatelli ends)

Stoich 15.0
WOT-13.2

Test 4- Granatelli MAF (stock)
Stoich- 14.1
WOT- 12.0

Test 5- Granatelli MAF (stock GM divider ends)
Stoich- 13.7
WOT- 11.2

So, there are the results and effects of ported ends on AFRs
It is obvious that ported ends do lean out the mixture a lot (.3 stoich and .7 WOT from my base)

The funny thing is that with them on, it kinda took away the nitrous tune to give me an almost perfect NA tune

Also, a remark was mentionned on the board that eventually the PCM would learn and go back to the original setting and that is false (in my case at least).
I drove over 350 miles with the ends on and the readings never got richer. Once you fool the pcm, it stays fooled, since it never reads the un-metered air going in and my tune is in open loop.
I have an import with no O2 sensors (front or back).

 

So forgive my ignorance.

But surly if you have some form of tuning software (LS1edit, HPTuners) could you acheive exactly the same results via tuning but just sticking with the stock MAF?

 

Oh, yeah, of course. This wasn't done to tune the car, it was done just out of curiosity, to see the effect a simple MAF end change would have on the air fuel ratios.
since I had the Granatelli from long ago, I just used it for the tests.
Kinda like a myth buster test if you like

It just so happens that with my nitrous tune (rich at WOT), putting the ported ends on leaned my mixture just right.

 

What ratio is supposed to be best for reasonably safe WOT power?

 

Did you happen to log timing advance during these runs? I would be curious to see if it had different advancement because its reading a different airflow.

 

Well that depends on a few variables.
The main one being fuel octane, but includes advance timing and DCR.
I'm able to run very lean at wot with 14.1 on 26* timing and TR6 plugs gapped .035, before I start registering any knock, and that is because our fuel is 98 Octane. But best power is made around 13.2>13.5.
But with US gas, on 93 octane, 13.1>13.2 is the average norm with up to 28* timing.

 

Actually no, not yet. I've been curious about the same thing too.