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



More information about the Diy_efi mailing list