1/4 Wave Tuning
Chuck Tomlinson
tomlinsc at ix.netcom.com
Tue Jun 18 18:06:02 GMT 1996
Donald wrote:
>
>Does anyone know the exact reason for the "1/4 wave tuning" modules (or that is
>what GM shop manual calls them) on the intakes of a lot of vehicles?? It appears
>to me that it is just an extra box or chamber in between the air filter and
>the throttle body
The module is called a Helmholtz resonator, and its primary (I think only) purpose is noise reduction near a particular frequency.
>... My Formula Firebird has one as well as most SFI and CMFI
>injected pickups and vans) ... My only guess is that it is a method of "tuning
>the intake" kind of like length tuning of exhausts... My next question is how is
>it's volume calculated? 1/4 wave of what? How much extra horses does it
>produce (if any)? Also, does the shape matter?
According to the Bosch Automotive Handbook,
Volume = (Sm/l)*(c/omega)^2, where
Sm = avg. cross-section area of the runner
l = runner length
c = speed of sound in air
omega = resonant frequency = 2.pi.f, for f in Hz.
AFAIK, it adds no power (maybe reduces power slightly), and the shape does _not_ matter. I don't know why the GM manual calls them "1/4 wave" modules, because the volume (not the length) is the important parameter for a Helmholtz resonator.
Chuck Tomlinson
tomlinsc at ix.netcom.com
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