Originally Posted by No Tread TommyG
There are "draw through" which go before boost, and "blow through" which go after, between the turbo and TB.
Just make sure you get the right one : )
The meter electronics measure air mass and don't care whether they are before the compressor where they might see anything from ambient pressure to a certain degree of vacuum or after the compressor where they might see less than ambient pressure to boost. They just provide a voltage in proportion to air mass to the EEC where the EEC takes this voltage and looks at the various calibration tables to calculate the required injector pulse width to achieve the desired air fuel ratio. If you have a calibration sheet that came with the meter and a way of programming the EEC such as a TwEECer then you take the meter calibration data and input the transfer function directly into the EEC.
The only differences that I have noted have been in the physical housing design. Meters need to have a retaining 'lip' where the hoses attach otherwise they will blow off under boost. The older 'bullet' meters were like that with no lip and were no good for boost. Also some plastic meters will just not stand up to boost pressure.
I have a run a stock Ford meter under boost and it works fine. I currently have an older Pro-M Univer aluminum meter which was run downstream by the previous owner and now upstream in my set up and it works fine.
Also the difference between a meter sold for a supercharged application and one sold for a normally aspirated application is in the meter calibration relative to the stock transfer function in the Ford EEC. The supercharged meters transfer function is designed to be 'fat' at higher flow values so that under boost it will ensure that the motor does not run lean and risk detonation. This is just fooling the EEC to get the desired results, by far the best way is to change the parameters in the EEC calibration that you want such as air fuel ratio.....