Intake runner sizing..

[Edward Hernandez R]

"Also, c is not equal to the speed of sound exactly, but the sonic
speed of the inlet gases."

c is, in fact, the local speed of sound, which is dependent on air temperature, which depends on where you measure it. For this equation, local means IN the intake manifold, and can be determined by the following formula:

c = sqrt(gamma*R*T)

where sqrt means square root
      gamma for air is 1.4
      R for air is 287
      T is temperature in Kelvin, which you get by adding 273 to the
            temperature in Celsius. 27 degrees Celsius is the same as
            300 Kelvin.
Thus, c for air @ 27 degrees Celsius is 347 m/s.

"Is Vswept the volume swept by the piston?"

Yes, actually it is. The formula posted divides this in half and accounts for compression ratio to derive mean cylinder volume. 

"When I worked it out I got the inverse of units of length %-( So I'm not too sure what's up with that.  I'm going to ask my professor about it."

The formula that was posted will give you frequency because it has c in the numerator. The formula in the ASME paper(page 3) does not have c in the numerator(one of Engleman's mistakes) and will give you the inverse units of length.

"And it is still very 'iffy', because it really only works for tubular intakes, and designs where you can accurately measure all lengths and volumes."

My earlier post states other restrictions(included below) for this formula, but it defintely WILL work for non-tubular intakes. As far as accurately measuring lengths and volumes, what you can measure with your tape measure will be good enough for members of this list, and the frequencies you calculate will be ball park. Suffice it to say, this is as accurate as anyone can expect who doesn't have access to engine modelling software which can account for wave propogation, Navier-Stokes solutions, unsteady flow, blah, blah, blah. Have fun with it!

Snipped from my earlier post:

"Somone later posted the correct equation(referred to in the industry 
as the Helmholtz method). For mean cylinder displacement, divide the 
cylinder displacent in half regardless of whether it's a piston or 
rotor. CAUTION: This only works for 4 cylinders or less, and will
 approximate the rpm where volumetric efficiency will peak, not how 
high the peaks will be. If you're good and select the right
combination of lenghts and areas, you will get two peaks. The SAE 
paper where this can be found is 900680. The original which this paper
 is based on is an ASME paper by H.W. Engelman "Design of a Tuned 
Intake Manifold". The latter is a great tuned intake primer for this
 list, the first has a sample calulation.