re: toys and airflow measurement

["Janet Scruggs" <scruggs@mbay.net>]

Dan,  it is easier to measure pressure than airflow.  The analogy is similar
to measuring voltage and amperage.  For amperage you should be in series
with the circuit, but voltage can be measured in parallel.  Yes, there are
many assumptions in the previous two sentences but this is not intended to
be a definitive work, just a 'how to'.  And here is... how to.  Just measure
the pressure.. vacuum is pressure, after all... in the intake manifold to
check the restriction of a filter.  The more the vacuum _at a given throttle
setting_ the greater the restriction.  Pressure is the basic component of
measuring air velocity.  You can either the velocity, or you can shorten the
process, just look at the pressure and make your evaluation with that input.

If you want to be further upstream from the pulsing of the intake valves,
then look for any vacuum line in the air filter housing, tee into the line
with a gauge.  If there is no port then make one.  Drill a hole in the
plastic part of the filter housing downstream of the filter and screw in a
metal fitting to attach a line for your gauge.   Either put a screw in the
opening after you're finished... or just cap off the fitting.

Key in measuring subtle differences that are likely to be found at a given
condition is the sensitivity of your gauge.  I've not tried it but suspect
that your average automotive vacuum gauge may not have the sensitivity to
differentiate between varieties of air filters.  The digital gauge that is
part of the control unit of my HKS Electronic Valve Controller has a
sensitivity of 0.01 bar but I haven't a clue where one would find something
similar.

If you are really anal retentive... I mean precise... then we can actually
design a tiny air velocity measuring probe based on the work of Pitot, who
first measured the velocity of the river Seine at the request of the king...
sorry, I don't recall which one. This probe uses the pressure difference...
the delta p... between the static and dynamic pressures of the fluid which
you are measuring and converts it to velocity.

Regards, Gross