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