i think we need to organize and send a 85mm maf + hitachi/bosch sensor to Pro-M to get exact calibration values...

So this is not totally relevant to me7 but i am starting to tune a hitachi sensor(ford 0-5v style) on my me3.3.1 M3 turbo this winter.  Ive been reading up a little on these sensors(this post) and the "calibration".  What i am trying to understand is, how does prom "calibrate" these to a specific injector size etc? what are they doing?

my current thoughts are that they calibrate the sensors internally, to match injectors as said in this thread.  They look at the internal calc of the sensor to scale to an injector size to remove the tuning aspect on the actual car's ECU.  just scaling.

how do these sensors work?

I think its a voltage input to the sensor, and it measures how much voltage is needed to satisfy the hot wire to a certain temp.  does a calculation and gives a voltage output.  this calculation that is done is modified by companies like prom to match the factory sensor, or scaled in a way to make a plug and play solution with larger injectors, and working with factory ecu with little modification to the actual ecu tune?

if you have the full option of ecu tuning, like us.  we can use the factory ford transfer function for the specific maf sensor(found in a ford .bin file) and find a way too get a base transfer in our ecu's. 

the only reason to have a prom maf is to have a supplied transfer function chart, which would be awesome to KNOW what that maf is doing in that car with YOUR piping. 

I intend on running blowthrough with my M3, theres a company called TRM that does just this with thier OBD1 tunes, though id prefer to learn this on my own, seems like fun!

any thoughts or comments on this?

Agreed. I think the challenge with blowthrough is getting an accurate transfer function chart, because it is (as far as i know) difficult to reproduce blowthrough-like airflow characteristics on a bench w/o an engine dyno.

Perhaps what you could do is stack a known maf onto your intake pre-turbo along with the blowthrow maf, and use that to calibrate..

Pretty cool idea.

If you have a Zeitronix ZT-2 you can hook up one of the MAF's to one of the ZT-2's auxiliary inputs (it's got two), and synchronize them via RPM to construct the linearization curve for the blow-though.

You might be able to use rear O2 inputs if you have them coded out.

Yea i've always wanted to set up my wideband to feed into the rear O2 inputs but never got around to trying it out... let us know