Plenum sizing (a little off topic)

[Scott Knight]

Bernd,

> The plenum size isn't as important as the resonance characteristics.
<snip>

Here is the part where I turn into a complete putz.  My understanding
was that the runners set up the supercharge frequency by themselves with
their shape, area and length.  Then the plenum was the Big Damper that
allowed you to run a single throttlebody and have all the intake port
entrances see the same pressure (within reason).  The bigger the plenum,
the more damping and consequently possibly soggy throttle response if
too big.  Seems the pressure waves that come up from the closed valve
reflect back into the port at the opening in the plenum.  I know this is
basically what you said, but that 'resonance characteristics' part has
me a little confused.  I didn't realize there were plenum shape (?)
considerations.  This could easily turn into a whole study all it's
own...

I know there have been engines with variable plenum designs.  The VW you
mention, and the V6 SHO Taurus is the first that comes to my mind.  My
understanding was that the SHO just opened the valve between the two
halves to make the plenum volume(s) twice as big somehow enhancing high
rpm performance.  Thought it was strictly due to the volume.  Is there
more?

thanks.
-- 
Scott Knight  mailto:scott at scottknight.com
http://www.scottknight.com/ IRC:SS396man
'95 Black Impala SS
'94 Ducati 900SS CR
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