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
-----Original Message-----
From: owner-dakota-truck@buffnet.net
[mailto:owner-dakota-truck@buffnet.net]On Behalf Of Marty Galyean
Sent: Tuesday, September 19, 2000 10:25 AM
To: DML
Subject: DML: Why the stock 4.7 air hat is special
I posted this replying to the spark plug thread and there was no
response. So now I'm giving it its own subject. C'mon guys, its
not _that_ boring. Don't leave me hangin'!
I was taking a better look at the underside of the stock 4.7 air
hat and I think I know why you guys lose a bit of low end with
the intake upgrades. They have a 'Bose chamber' in the air hat
which will make the intake resonate at a lower frequency than the
normal intake of that length would resonate. This will cause the
intake to have its peak ram effect at lower rpms. As some of you
may or may not know, as the intake valves open and close, the
charge accelorates and brakes like a slinky or traffic. Given a
certain desired resonance, when the valves open again, the air
waiting outside is a pressure wave and not a rarefied valley.
Longer intakes lower this resonance, shorter raise the resonant
frequency. The frequence of the pressure waves is rpm dependent.
Those Bose desktop radios with incredible bass response for the
speaker size use the same principle. I know that some companies
are experimenting with variable tuned intakes that change
resonance continuously with rpm.
I was thinking of sticking with the stock air had but put a
solenoid driven butterfly valve that closes the entrance to the
chamber at higher rpms and see what happens. This should push
the resonance back up where the higher rpms can make use of it.
Marty
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