Air flow measurement - again...

[Mazda Ebrahimi]

> 
> This is where I keep coming back to measuring pressure drop across
> an opening (i.e. throttle).  Knowing temp (and maybe RH), seems t'me
> one could know very well the mass of air -- and the direction it
> was flowing!
> 
> Tom Cloud <cloud at peaches.ph.utexas.edu>

Hi Tom,

The problem with measuring throttle angle, delta P, and temperature is 
that delta P approaches zero as you get near WOT.  Let's take an engine 
that generates 400 Hp at 6000 RPM.  If this engine generates 100 Hp at 
2000 RPM and let's say 150 Hp at 2500 RPM (both at WOT), the throttle 
method won't be able to measure any difference in flow because in both 
cases manifold pressure equals (within a couple inches water column) 
atmospheric pressure.  To complete the calculation, you need to read 
RPM, in which case you are back to the speed density system.  In other 
words, the throttle measurement is only useful if the THROTTLE IS the 
restriction.  At WOT, the restriction is the intake valve, not the 
throttle.

Best Regards, Mazda