You found the 'Z' tube which John designed. The frequency changes from the
Bose chambered air hat (deep mellow sound to a heartier beefy muscle car) to
the Z tube design. On the Z tube it has been noticed the length of tube
brought back the lost low RPM feeling during initial tire spinning. While
the Air Raid gained from mid to top RPM range and lost out on the bottom end
range.
This is why I switching from this short style to a longer smooth bore tube
to the front left side opening. I will order John 5" cone today that will
be quite adequate for at least 700CFM (the 4.7 TB is rated around 600CFM
plus). I have noticed his design cone has a tri-flow into the cone and will
eliminate any turbulence that occurs on the on round cone.
I would go for the S version or Z version of the air intake tube.
-------------------------------------------
Steven St.Laurent
Test Engineer
Test Branch, GSD, MCTSSA
MARCORSYSCOM, USMC
760-725-2506 (DSN 365-2506)
Work:mailto:stlaurents@mctssa.usmc.mil
Home:mailto:saint1958@home.com
-----Original Message-----
From: Marty Galyean [mailto:mgalyean@acm.org]
Sent: Saturday, October 14, 2000 2:41 PM
To: DML
Subject: DML: ABS looooong po'boy intake installed on 4.7 - wow!
Ok, I should be doing laundry and cleaning up this pigsty, but
instead I will lay this on the list. Yes, I am procrastinating.
Note: You will need to use a fixed width font for the diagrams to
read correctly:
The other day I posted that I had replaced the air hat on my 4.7
with a curve of ABS and it made 'quite a difference', it looked
something like this:
9 |
---+---------+
/ | | stock
7 / | | air box
/ --+---------+
/ / |
| |
+----+
| |
+-+ +-+
| |
| TB |
| |
| |
When my K&N cone came in I installed it where the stock air box
normally sits (ala quickd shorty) and it improved the high end,
but the low end noticeably dogged. I really didn't give the
computer a chance to settle on this interim configuration as I
only put about 100 miles on it that way. From my experience with
my 240Z I knew that for resonance in a realistic rpm range that
it would need to be longer. In the time I had it this way it
didn't seem to get much better than the initial improvement:
+---
9 | ---
---+---------+ ---
/ | | K&N |
7 / | | |
/ --+---------+ ---
/ / | ---
| | +---
+----+
| |
+-+ +-+
| |
| TB |
| |
| |
Three days ago I put the longest ABS config I could design easily
between the TB and the cone and wow, what a difference!
Definitely some ram effect occurring at low rpms now! I can now
usually spin from a standstill again with the snugtop shell on
which I couldn't do right after installing the shell.
I used 4 90' small radius bends coming off the TB in roughly an
'S' shape that ended up pointing along the fender well, then put
a straight piece on down to the cone that sits at the 'radiator
gap'. The 'S' isn't totally flat; this allows it to fit in the
space and then angle down to the cone. I had to nudge the tranny
dipstick toward the TB to make room:
----
/ \
/| |\
/| |\
/ | K&N| \
/ | | \
/ | | \
/ | | \
---|----|---
| |
| |
---+--- | |
/ | \ | | 8
7 / | \ 7 | |
/ --+-- \ | |
/ / \ \ | |
| | | | | |
+----+ +----+ +----+
| | | | | |
+-+ +-+ \ \ / /
| | =+=\ --+-- /
| TB | | \ | / 7
| | | 7 \ | /
| | | ---+---
|
tranny
dipstick
I would like to try the following sometime to see if it raises
the resonant rpm as I predict (but I think the long one installed
is probably ideal for street use):
----
/ \
/| |\
/| |\
/ | K&N| \
/ | | \
/ | | \
/ | | \
---|----|---
| | 2
+----+
| |
4 / /
---+---------+--/ /
/ | | / 7
7 / | | /
/ --+---------+----/
/ /
| |
+----+
| |
+-+ +-+
| |
| TB |
| |
| |
All the numbers are eyeballed (lazy) lengths in inches. Each
curve is approximately 7" in length (guestimate based on length
of inner and outer curves). So the single curve setup (quickd
shorty style) is around ~17", the middle (which I have not tried)
is around ~20" and the long one that I like so far is at ~36".
This would give them rough basic resonances at 423Hz, 339Hz, and
188Hz. The longer the tube, the lower the resonance (ala tuba
vs. piccolo). All these are in the audible range. The
calculations are based on sea level speed of sound and a
non-moving mass of air (don't know if that matters!). But
assuming the air is on the vacuum side of outside air pressure,
the speed would decrease and the numbers above would be lower.
Here is the simple equation:
speed_of_sound (in ft/second)
resonance (cps) = -------------------------------
2 * length_of_tube (in feet)
Caveats:
I don't know how twisted the math gets in the extreme velocity of
an intake, nor exactly how to compute the length of the curved
sections with regards to air columns etc, but that is the general
idea.
I am not taking into account the distance from the intake to the
intake valves which I am sure is a factor.
I am using the equation for a close tube. There are other
equations for tubes open at one end and open at both ends. I
think the filter is enough of a resistance that it would read
mostly 'closed' accoustically (which is why there is a ram tuning
effect in the first place). But am not sure whether the valves
should be considered opened or closed.
But I'm trying to get exact numbers at this point, just a rough
idea of the amount of variation possible.
So no matter what the details work out to be, there is a big
difference in resonant frequency as the length changes.
FWIW, DML'ers.
Keep on Dakkin',
Marty
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