custom intake dimensions and intake/header tuning

[George Roffe]

Rick Frey wrote:

>On a speaker building list I am on

WOOF ;-)

>a guy just got blasted for posting off topic about his car.  Someone else,
>being a wise guy, talked of tuned intake runners and the direct
>comparability to properly tuning a bass port for a ported speaker.

What?

Getting blasted for being off-topic?  What a concept. ;-)

>However, in the speaker world you don't need a dyno or 1/4 mile strip to
>measure, only a proper PC.

Not *entirely* true Rick.  From the time I was on the subwoofer list I
realized that you can make your calculations and build a damned good
speaker from it.  But....  People still use diagnostic tools to fine tune
their speakers.  I've been off that list for a year now and cannot remember
what it is they use, but I remember reading much about instrumented testing
of their subs.  That would be the equivalent of dyno tuning your car.

>so.... Are there similar equations available for calculating the length
>and diameter of intake runners or exhaust header tubes that are pretty
>good at predicting gains at various RPMs?

Yes.

I don't have them however.

Mike?

>Will anyone discuss the appropriate equations and tell if they are
>accurate at predicting the response of the engine to those length and
>diameter parameters?

Oh yes!!  I'd like to know.  In fact, I just had a conversation on Rennlist
(Porsche list and forum) about header tuning.  Unfortunately, I don't know
the formulas.  I'd like to because I know that the commercially available
headers for the 944 aren't much to write home about.  But, a major race
tuner claims to get good results with headers built to his spec.  I've love
to play with the calculations a bit.

>Here's a quick, uneducated guess.   Target RPM/2 = frequency at which you
>tune the port.  Ah, but where do I measure?  From the valve to the other
>end?  etc

Well, here is were it gets complicated.  You will get a wave reflection at
the MAF as well as the opening of the tube.  Luis Molina played around with
MAF placement within the CAI tract and was able to improve his
output.  Pretty interesting huh?

Excellent topic, and you're right, the concept is pretty similar.

George Roffe