Of an OEM airbox, and an open filter with 10" of straight section between the filter and maf. Hardware and software are identical besides the pre-maf piping/filter, and the car with the lower maf readings has a 3" downpipe vs. 2.5" on the higher reading car. Both logs were taken using the same maf sensor swapped between the two cars. Logs were taken 20 minutes apart. Before I go digging for intake leaks between the turbos and maf on the lower reading car , does anyone have an opinion if there should be this large a difference? I don't normally deal with open element setups, but have done a handful of stock airbox cars with this same hardware combo.

Details:
Stock block 2.7T
BW K04
85mm straight maf housing


Thanks, guys.

The baseline is the OEM RS4 airbox with a paper filter, then I've installed the x34 intake and put a HKS mushroom filter, as you can see
the turbulent air makes the MAF read low which in turn makes the AFR lean out, then went with a conical BMC filter, which would foul
the MAF and read higher, which makes the AFR rich, then installed the AEM dryflow which is provided with the kit, and this is the only
filter that comes with a built-in velocity stack and that helps a lot.

Looks like your results are very close to what I'm seeing. This would also explain a few things on a few other cars, and not pegging the maf despite having very similar hardware and boost levels. I made a graph with 5 different cars all using the same housing, and the one with the open element was the only one much lower than the other 4 by about 75 g/s.