Air Flow Meter vs Turbo

["Michel Drainville" <MDrainville@xxxxxxxxxxx>]

To the Air Flow Meter experts on the list, and others,

I'm in the process of installing a turbo on my M42 engine. It's not a kit,
I'm doing it from scrath.  Before
starting the installation, I decided to measure some signals to have a
reference, before/after.

This morning, I checked the AFM. With the engine stopped, I get a voltage
ranging from 0.26 for a closed flap,
and 4.89 for a completly opened flap.I then tried the car on the road. At
idle it's around 1V, cruising is around 2.9 to 3V, and at WOT at 6300 RPM I
got 4.65Volts.

I'm wondering what will happend when the turbo will push more air in. Let's
say I run at maximum 7.5 pound of
boost, it's 50% more air, right?  By doing some reverse math, I figure that
to obtain 5volts, I only need to run
at 1.xxx psi.

Am I missing something?  The Downing Atlanta supercharger running 5-7 psi
uses the stock AFM.  Also the turbo
companies making kits for 318s and Z3 use the stock AFM, and pretty sure
the stock chip also.

So, is it because the AFM doesn't give a linear signal, toward the end of
the movement of the flap, the spring
tension is greater??

Do I need to recalibrate my AFM? I hope not.


Any help will be appreciated.

Michel Drainville
91 318ic (turbo... on day)

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