Originally Posted by fahr_side
I think either you're a little confused about what these terms mean, or your tuner is. For your sake I hope it's the former!
MAF = Mass Air Flow. MAF is a calculated value derived from the voltage required to keep a filament in the sensor heated to a given temperature. The more air that passes by the sensor, the more voltage is needed to keep it warm.
The housing itself does not really get 'maxed out'. What happens is that at a given amount of airflow, there is so much air passing through and it cools the sensor so well that sensor voltage rises to it's maximum of 5 volts. At that point more air can still pass through the housing (by accelerating and flowing faster), but the sensor can no longer measure how much more. Obviously this will lead to a situation where air flow will increase but the ECU will not command extra fuel to be injected. In this situation it is possible to fit a larger housing. The sensor then 'sees' less of the flow through the tube and MAFv is then lower for a given flow volume. Of course the MAF scaling then needs to be recalibrated.
Whether the tune is done via Opensource or commercial tools does not affect the hardware involved nor the laws of physics!
For your reference, a lot of people are running 18G turbos to their max on the stock intake and MAF housing with MAFv never reaching 5 volts. The 18G will hold at least 18psi at redline at good efficiency on a typical EJ255 install with stock cams.
I'm sure it's me using incorrect terms and such. My tuner has tuned 2k+ scoobies snece 01 including some that are currently in the recored books.
I also think I have a brake hanging up to, my car doesn't "roll" to a stop like it should.