Speed density or HPXE blowthrough something along those lines.

You will need 90 mm
Even if you hit 5V at sensor don't worry, lambda corection will do yob for that few more g/s

.Can you expand the shortcut? I realize I missed the development of me7 by at least 10 years but I want to get to know it more, I play with my car and I do it for myself

The elements on HFM5 are different with different measurement capability.
There are standard and extended range versions, at least 3 different ones.

If you take two different sensors and put them into 90mm tube then one will read lower, one with read higher.
It makes a big difference which sensor you use.

Also, in a 90mm tube the car won't work well on low load and idle on 1.8T, the air flow will be all over the place.
The turbo inlet is probably also not 90mm.
The RS4 MAF, that has the extended range sensor is 83mm internal diameter, and this tops out at around 600hp, and already the 1.8T engine does not work too well with it.
That is why the HPXE is a better choice.

I work with 83mm case + maf sensor from BAM + gtx2871r with MLHFM adjusted. Idle is very stable, after a lot of works because i had a bad idle reve from high rpm , idle goes to 650-680rpm and in one sec goes to normal. other problem is maf at throttle is different like maf reading in logs, but i adjusted from Kfurl. I think you can try!
PRJ what do you think about SPEED DENSITY. Is it worth. For speed density must have a good map sensor , right? I can not use a 4 bar stock bosch map sensor, right? Many peoples recommand AEM map 0-5BAR

Prj made it perfectly clear that inserting maf at this stage would do more trouble than good. Maf that would see the top of the flow at idle will be useless read hfm5 pdf. I can use a larger map 4 bar. And someone sent me a message to check fueling by part throttle

Is there a C167 based ECU that we could copy the frequency input code from?

Im very interested in that for Siemens MS43 and frequency MAF and frequency ethanol sensor.