volumetric efficiency

[orlin steven jared]

> "Inertial Supercharging Effect:
> 
> When the intake valve starts to close, the fast moving air column 
> tries to keep ramming itself into the cylinder. If the inlet
> valve is closed at just the right instant, the extra charge will be trapped
> in the cylinder (called inertial supercharging).  Volumetric efficiencies
> up to 130 percent can be obtained......."

I think this is mentioned in the ASME paper "design of a tuned intake",
probably where superflow got it from ;-)

> They then go on to define the inertia-supercharge index Z, which
> is an empirical value which is a measure of the strength of the
> inertia supercharge.  To compute this:
> 3) Compute Z:
> 
>      Z=((RPM/126000)) * sqrt((CID * Inlet Length)/(A))
> 
> Z will usually be between 0.9 and 1.2 
> 


This looks like a 'makeshift' Inlet Mach Index formula.  (I could
be wrong).

The Inlet mach index is the ratio of the typical inlet velocity
to the inlet sonic velocity.

Z = ((b/D)^2 )* s /(Ci*a)

pg 173 of Taylor's book.

Where b = cylinder bore
D = inlet valve diameter
s = mean piston speed = 2 X rpm X stroke
Ci = mean inlet flow coefficient
a = local velocity of sound


a can be calculated by multiplying a constant by the square root
of the temperature (absolute).

Ci is the hanger here.  It correlates to the ratio of the lift/inlet
valve diameter.   But my guess is that for whatever you need to
come up with a mach index for, an approximation is good enough ;)

There are graphs for Ci in the book too.

The reason why I have doubts that maybe this isn't the same
"Z" factor as Bruce posted is because you don't want a value
of over .6 for the inlet mach index.  volumetric efficiency starts
to drop off fast after that. I didn't hack through the math/units
to compare the two, but they look similar. 



Steve