Mat,
Chris started with his ":straight through" muffler
which consisted of a 5 inch outer barrel and a 3 inch perforated
inner pipe that went end to end. (28% x 1/8" holes) Between the
two is the Innox packing for sound deadening.
To mount this directly onto the engine, 3 holes were cut through
the outer skin and through the inner perforated inner tube on one
side only. THe 3 exhaust pipes go just inside the inner tube
only, so that the exhaust is aimed at the opposing side of the
inner tube, not quite 3 inches away. It appears that the packing
between the inner tube (perforated) and the outer skin has been
degraded by the pounding of the exhaust on the opposite side of
the inlet tubes. The exhaust does not in any way exit through
the inner holes stamped into the center tube. The exhaust enters
the center tube (hollow) via the 3 inlet pipes, and then a 4th
exit 2.5 inch pipe is cut into the center cavity to allow the gas
out.
As I said in discussion with Chris, the fact that the gas now had
to swirl over the small center holes before finding the exit,
appears to have done a great deal of silencing, over just the
straight through flow. He claims a minimal loss of power but not
enough to worry about.
The 3 tubes are welded only to the outer barrel as impossible to
get in the center. I am also surprised that the welds did not
crack with no expansion joints. The single exhaust pipe has
cracked, but has about 2.5 feet of exhaust swinging on it.
Hope this is clear? Neil.
What did you mean by " The 3 inlets
fire directly onto the opposite side of the center tube." So
the 3 primary tubes are welded to the center tube, which
blows out into the outer tube (that has the packing), then
out the 2.5" pipe. How does the packing not blow out the
2.5"?
I'm curious
about hard welding the 3 inlets to the outer can without
any expansion joints. I was worried so I made all 3
expansion joints.
Darn, I'm thinking I put way to many holes in the perforated
center tube.
- Matt Boiteau
On 2020-01-21
4:20:29 PM, Neil Unger 12348ung@gmail.com
<flyrotary@lancaironline.net> wrote:
Mat,
Here again I am just the messenger.
The guru is Kevin Davis from Active Exhaust Systems
(AES). (woolongong Aust) Yes 28% is the magic number as
is the size (dia) of the holes at just over 1/8"(critical
apparently). Packing is Innox wool which is fine S/S.
Too much and too little, both affect the result. Kev,
claims that he weighs the muffler when packing to get the
right amount, says that although not packed precisely
even from end to end, it will even out as it works.
The big can has the perforated tube running end to end
which is hollow (perforated tube) and the outer can is
packed with Innox between the inner perforated tube and
the solid outer tube. The muffler shown, began life as a
straight through muffler which was mounted under the RV.
Chris then as usual adapted the muffler by cutting 3 x
inlet holes right into the hollow center tube, then welded
it to the manifold plate. The 3 inlets fire directly onto
the opposite side of the center tube. I tried to see what
that has done to the "wool"opposite, and it appears to
have blasted some away. Hard to tell looking through 1/8"
holes, Only way to find out is to disassemble it. Then to
get the noise out, he again simply cut another hole
halfway between the back 2 exhaust inlets and welded a
2.5" outlet. Has done many successful hours Chris says.
Chris cut off the 3" inlet and outlet tube and welded a
plate over both ends to seal the whole muffler. It fitted
in the small space available and worked which is what
matters
Kev. seems happy with a 2.5" exhaust tube, so is up to
you if you chase 2.75". Here again I have no idea, and I
suspect most others have little idea as well. really a
dyno is the only evidence. Watched many Utube videos of
blokes putting different mufflers on their cars to get a
lovely "quiet" exhaust. All terribly successful according
to the operators, but IMHO the results ranged from little
difference to actually louder. Perception and fact can be
totally different., AS they say if your baby cries it is
music, if it is someone elses you want to kill it!
Neil.
Only 28%.
Geesh, I just drilled mine and did about 200%, I guess
that is way to much. I guessed the drill area to be
double the size of the pipe. Did make design so I can
drill out one cap and switch out the inner pipe full of
holes to test different back pressure. Neil, can you confirm
28%?
Is the big can stuffed full of wool, so the primary
tubes fire right into it? How does it exit out that
bottom pipe?
In RX8, they (car forum) say 2.75" is the best (but hard
to find) exhaust size. But since we are taking large
harsh pulses and bring them down to a small constant
flow, they say you can run smaller size. I did my
downpipe as 2.75" and will do the long exhaust
underneath plane in 2.5"
- Matt Boiteau
On
2020-01-20 8:24:41 PM, Neil Unger 12348ung@gmail.com <flyrotary@lancaironline.net>
wrote:
Second
time with 1 photo each to get past the editor!!
Photo of modified straight through muffler to attach
directly to the RX8
engine. The science apparently is to have approx
1/8" holes that amount
to 28% of the area of the through pipe. This one is
3 inch but the
Manufacturer claims that 2.5" is better. Dia is 5 "
and the space
between is packed with fine S/S "wool". THis is the
first bloke that can
tell me the science in mufflers as he has made them
all his working life.
JUst passing this on as I am totally ignorant as
usual. Still trying to
mount my turbo if I live long enough.
More photos to follw for those interested. Neil
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