custom intake dimensions and intake/header tuning

[Rick Frey]

On a speaker building list I am on, a guy just got blasted for posting off
topic about his car.  Someone else, being a wise guy, talked of tuned
intake runners and the direct comparability to properly tuning a bass port
for a ported speaker.

Now, in the speaker world, the acoustic resonance used to tune a ported
speaker is well defined and the equations to calculate the size (length and
diameter, which are integrally related) are well known and quite accurate
at doing their jobs.  The predictions are very close w/ minor tuning of the
port while measuring.  However, in the speaker world you don't need a dyno
or 1/4 mile strip to measure, only a proper PC.

so.... Are there similar equations available for calculating the length and
diameter of intake runners or exhaust header tubes that are pretty good at
predicting gains at various RPMs?  We all know that, generally, short
intake runners make more power at higher rpms and long ones get us a
resonance that works at lower RPMs.  But that has to be a crude rule of
thumb because a change in the  cross sectional area of the runners would
dictate a change in length of the runner.  i.e. I could build a short
runner intake that *could* resonate at a low rpm frequency but its diameter
would be too small for practical purposes.

Will anyone discuss the appropriate equations and tell if they are accurate
at predicting the response of the engine to those length and diameter
parameters?

Here's a quick, uneducated guess.   Target RPM/2 = frequency at which you
tune the port.  Ah, but where do I measure?  From the valve to the other
end?  etc

TIA,

rick frey