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Strange. I just pulled it up again, and
the 1st try kinda glitched with a flash of 'unavailable', and the
2nd try shows $140/ft for 16 ga 2.5". I also noticed that there
was something in my 'cart', and when I looked, it was 1.5" at
$21/ft, so it changed the size I requested. Sorry for the
misleading info.
On diameter, are the car guys running mufflers and full-length
exhaust (to the rear of the car)? Length and number of bends have
a major effect on flow resistance. 30" vs 20 feet will make a
difference.
For perspective on materials, several guys are successfully
running Aeroturbine mufflers, which are made from 304 stainless. I
wonder if distance from the exhaust port allows the lower grade
alloy. It's pretty well documented that EGT drops quickly as you
move away from the port. The piston guys get significant
variations in EGT between ports with probe distance varying by
even an inch or less.
Charlie
On 12/20/2019 10:18 AM, Matt Boiteau mattboiteau@gmail.com wrote:
You have to be careful
on the Burns site. When you click their dropdowns, other
dropdowns change automatically to match their
stock/availability. Biggest they have for 16ga is 2.5" @
$140. The largest size they have is 3.5" but it's only 20ga
which I think is to thin for the main body of muffler.
What exhaust size do most people stick with, 2.5" or 3" for n/a
? On the car forums, most are adamant to go to 3" for n/a Rx8,
but have no actual data as to why. Just thinking, bigger is
better. I can see turbo being 3", but I have a hard time
believing 2.5" isn't good enough for n/a.
- Matt Boiteau
On 2019-12-19
11:12:42 PM, Charlie England ceengland7@gmail.com
<flyrotary@lancaironline.net> wrote:
Anyone have a
good source (USA side) for 321 tubing? Looking to
rebuild a new exhaust like Gary Schwarz. 4" or 5" in
size. I've only found one place SPD Exhaust, that is
$130 a foot for 4inch tube.
- Matt Boiteau
On
2019-11-26 10:37:22 AM, eanderson@carolina.rr.com
<flyrotary@lancaironline.net>
wrote:
Interesting idea about the diagonal placement
of the discs, Charlie. When a disc did break
loose from the jam nuts and spung, it really
restricted gas flow, so I think welding the disc
in place is likely the best solution.
I think your idea about diagonl slots would
be worth trying. It may be that simply cutting
say 1/4 - 1/3 of the disc off for gas flow and
then alternating the side of the tube with the
slot in it would still cause the shock wave to see
a solid wall bounce back and forth between disc
(mostly) and still permit good gas flow.
Apparently the reduction of the shock wave in
the several sections did not result in the loss
you mention due to refledted shock wave.
You and Tupper have a great Thanksgiving.
Ed
------ Original Message ------
Sent: 11/24/2019 2:48:50 PM
Subject: [FlyRotary] Re: Mufflers
Ed, I really wish
I'd had a chance to hear those mufflers; I've
been fascinated by the idea since you first
mentioned it many years ago. Do you remember
what you were running before, and how much
takeoff rpm you gained when you made the
switch?
With only 5 washers, I wonder if the same
effect could be achieved using half-discs slid
into diagonal slots cut in the tube and then
welded around the cut. Cuts could be staggered
in rotation around the tube as you move down
the tube. Would likely need to 'break' the
straight edge of the half-disc to resist
fatigue. Small hole at the edge of the cut
would allow the 'break' to slide into the gap.
I would have expected at least some power loss
on a 13B because of the detuning effect of a
mis-timed reflected shock wave; good to hear
that it didn't. With a Renesis and no
intake/exhaust overlap, it shouldn't make much
if any difference to power as long as back
pressure is managed with a large pipe.
Charlie
On 11/24/2019 11:48 AM, eanderson@carolina.rr.com
wrote:
Sorry, Neil,
Been a while, it was two exhaust pipes,
one for each exhaust port. Mistyped, error
on the drawing the disc were 2 1/2" dia
inside a 2 1/2" dia pipe. The discs fit
snugg enough that when one broke loose and
spun on the rod, it scored the inside of
the exhaust tube. I got the discs from
McMaster Carr. Try oversize SS washers.
The tubes were actually glass pack mufflers
which had 2" dia inlet/outlet. I cut the
front off and then after inserting the discs
use wide metal clamps to put the tube back
together (welding would of course have been
better).
I do not believe that any of the
dimensions are critical except the discs
should fit touching the inside of the tube
if possible. I called them discs but they
were actually oversize SS washers with a
hole in the center for the rod. I ended up
with 5 discs inside each tube. I used the
spacing for the shorter 36" long tube. The
idea was to have a large portion of the
shock wave dissipated inside each segment of
the tube while keep the gas flowing
freely.
It was truly quite and like I mentioned I
could get 6000 rpm with my 13B on take off.
Large diameter tube/discs would likely
permit more/easier gas flow, but since I can
not weld, just finally gave up and went on
to other things.
Ed
------ Original Message ------
Sent: 11/23/2019 10:35:27 PM
Subject: [FlyRotary] Re: Mufflers
Ed,
On rereading your
post, am I correct in believing that you
had one pipe per exhaust? A total of 2
pipes? How many discs were in each
pipe? I may have misunderstood, but you
say you had a 2.5 inch disc fitted
inside a 2 .125" exhaust pipe. If
correct measurement how did you manage
to force 2.5 " inside 2.125" pipe?
perhaps the other way around measurement
wise?
Thanks, Neil.
Given the recent interest in
mufflers, I thought I would throw in
my experience with home made
muffer. I could hit 6000 rpm on
take off with my 13B with the
2.18:1 Gear ratio. You could stand
within a wing width with the engine
idling and bearly hear it. At 6000
rpm it was about 1/2 as loud as an
unmufflered lycoming.
The basic idea was to break up
the shock wave while minimizing
gas flow impedeance. I used 1/8"
thick 2"1 /2 Dia stainless steel
disc inside of a 2 1/8" dia
stainless steel tube. The disc
has slits cut from the outer edge
approx 1/2" toward the center in 8
regions as shown in the diagram.
Then each "tab" was twised 45 deg
from the plane of the disc. If
you looked at the disc front on it
look almost as a solid disc with
just a small slot area showing
through. The idea was that the
shock wave would basically see a
"solid or mostly solid" disc where
as the gas could still flow
through the slots around the
tabs. I had a threaded rod
extending the length of the tube
with jam nuts on each side to hold
the disc in place.
The reason for the rod and nuts
was not being a welder- I used
jam nuts - welding it turns out
would have been much better as the
nuts eventually became loose.
That was not good, when one of the
disc came lose it started to spin
and greatly impeded the gas
flow. Although folks told me it
sound cool - like a turbin winding
up.
In any case, I decided that not
being a welder there was no way I
could remedy the defects. I think
if there were some way to "spot
weld" the outer part of the tabs
to the tube and perhas to a rod in
the center the muffler would have
extend it useful time. I flew
approx 12 hours
including one trip to Tracy
Crook (first extended flight with
muffler) by the time I got there
at least one disc had broken loose
and was spinning. Tracy was kind
enough to use his welding skills
to weld the discs to the rod on
one of the mufflers (had two one
for each exhaust), but within
another 6 hours or so disc in the
other muffler started to spin.
Also I found that the shock wave
pounding eventual would break off
a tab or two since they were not
anchored and could flex.
Just thought I would throw the
idea out there in case it has any
merit.
Best Regards
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