A hot-wire MAF will work in ambient or elevated pressure. But only if it is hot-wire, or the obscure GM “cold wire” MAF, which is a Coreolis effect based mass flow meter.
A flapper door, or paddle wheel MAF must be ambient.
Where you have spectacularly fucked up is the LOCATION of the MAF. A good rule of thumb is that you need 5 diameters of straight, smooth, pipe before and after the MAF. Screens will help, you should NEVER remove the screen from your maf, it will ruin it.
The reason for this is velocity pressure. Your MAF meters airflow from the center of your tube, and releases it toward the side. This requires that the pressure and velocity be equal everywhere in the MAF. But since your MAF is WAAY too close to the bends, more air will be flowing at the OD of the bend. This will cause your MAF to be VERY in-accurate. I have done extensive testing of the effects of up and downstream tubing on the calibration of Granetelli aftermarket MAFS. The MAF is EXTREMELY sensitive to this.
To comment on Tom’s comment, you can have a BOV, vented to atmosphere, as long is it is BEFORE the MAF, wherever the MAF may be.
So you could go:
MAF, turbo, RECIRCULATING BOV
OR
Turbo, BOV (atmo) , MAF
OP: I have seen your car at LV, talked to you, and you seemed extremely cool. I enjoyed the chat we had, and if you want I can help you out with the MAF.