Re: RE: Why the stock 4.7 air hat is special

From: Marty Galyean (mgalyean@acm.org)
Date: Wed Sep 20 2000 - 02:05:01 EDT


When I think back on all the 'tube' posts, IIRC, many people would write
something to the effect that the low end is either the same or worse but 'wow,
once it hits the higher rpms it really takes off!'.

It seems likely that if the intake is resonating, the noise would be louder;
i.e. a tuba. So you may be onto something about the chamber being dialed for
low noise. I know that a problem engineers have with intakes is that they only
have one resonant frequency (and harmonics I suppose) and so they go to a lot
of effort to broaden the bandwidth of the resonance so that its not just there
at one narrow rpm range. That could very well be what the chamber is intended
for. Good point. A side effect of this could be less overall noise as
resonance at a particular frequency would be dampened.

Almost all the tuning stuff that applies to exhaust, also applies to intakes in
a twisted way. There are some differences: with exhaust, you want to get the
right balance between flow and back pressure to keep the scavenging at the
right level, with intake you want as high a pressure at the opening valve as
practical. Of course both systems are part of a larger system; changes in one
change the behavior of the other. For example; too much scavenging can be
corrected by more pressure in the intake to a degree.

Sleep time.

Rob Parenti wrote:

> My guess is the huge intake plenum is the main resonance chamber here, but
> no doubt this kind of tuning is significant. Most likely the airhat chamber
> resonance is used to tune the sound down, rather than the horsepower up.
> Those with intake tubes usually mention the difference in sound. If there
> really a loss of low-end when you pull the air-hat? I hadn't heard that,
> but I guess there's a lot I miss.
>
> - Rob



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