Hi Paul,

 I hope the  Oshkosh experience was very good.  The TTC project is
 very impressive.

 I’m gradually working through my radiator and oil cooler issues,
 and also building an exhaust header / tangential muffler.  I have a
 couple of questions on the latter.

 Please see the attached, although very crude, drawing.

 I am using the Racing Beat SS header, with short 2.5”x 1.75” OD
 .065 304 SS tubes welded in place.  These will slip into 0.65”
 1.88” tubes that will in turn be welded into a 6” 304 SS .065
 cylinder/muffler. On the front, a 90 degree 1.88” tube is used to
 reduce the length of the 6” tube and significant weight.

 Due to space and other constraints, I need to bring the 3” tailpipe
 (also .065” 304 SS) out of the *rear* of the muffler and up.  This
 gives me at least 3 options: 1. A straight 3” pipe welded to the
 rear of the muffler. 2. Squeeze the 3” tailpipe into a fish mouth
 (your previous drawings showed an area about 1/2 of that of the
 tailpipe). Or weld up a larger fish mouth. 3. Or, allow a short
 section of the 3” tailpipe to remain inside of the muffler, which
 could be  closed off and drilled with (e.g. 0.5”) holes to arrive
 at the same exit area as the fish mouth design.  I am wondering if
 this might be a more conventional muffler design and possibly allow
 better sound reduction?

 The prior concerns regarding the longevity of any metal living
 Â“inside” the muffler have been noted. However, with a Renesis
 engine having exhaust ports coming through the iron housings, as well
 as a cooling tube, both giving lower exhaust temps, do you think this
 is a concern for .065" 304?

 Thanks for your input,

 Scott Gettings

 You are on the leading edge Scott. Nothing like this has been built
 yet. The RX8 side port exhaust is  a little cooler so it should work
 all right. If it burns through opposite the exhaust ports you can
 weld on doubler patches.


 Paul Lamar


 Scott,  Suggest that you investigate 321 S/s as 304 is a very low
 grade Stainless.  Remember the exhaust temp will get up to 1800
 degrees which is rather warm.  Your design is similar to what I made
 and is still alive, but I have not the cooling tube.  Neil  Unger

 Nice work Neil.

 Paul Lamar


 Thanks very much for the input.  I researched 321, but it is not
 practically available in the sizes and shapes needed.  This is why
 I'm working with the thicker 304. I might could find some 321 plate
 and weld patches inside the tube directly across from the exhaust
 ports.

 Any suggestions on the size and area of the holes if the 3" tailpipe
 has a component inside the muffler tube (and a closed end)? I was
 guessing I could start with a bunch of 3/8" holes and a total "hole"
 area about 1/2 -3/4 that of the 3" tube. This would give a little
 back pressure.  Some of the holes could be enlarged in the future if
 needed.

 Scott Gettings

 I don't have that kind of detail. You are on the cutting edge scott.
 Do you have any room below the engine for a muffler?

 Paul Lamar


Paul,

No unfortunately the space below the engine is consumed by the oil sump and fuel header tank.   It is so tight I will have to pull the engine to pull a fuel pump!

We explored this option a while back. There is also no room to duct the exhaust  down and to the rear because it would interfere with the wing root.

Some of the pix you sent are of my engine.  I was planning on using a cut-down stock header feeding into a VAM — as per the previous attachments.  However, this was getting very heavy very fast.  This prompted me to abandon the stock header and incorporate a RB header flange into slip joints and then into a 6” VAM.  This will be about 1/2 the weight.  Another mockup is attached.  I’m hoping to have at least a few DB of sound reduction so I don’t get run out of the hanger condo association :-)

BTW in this pic you also see a mockup of two cross-counterflow radiators of about 15x20” cores (17x20 total).  The stock RX8 radiator can be shortened to fit these dimensions.

Scott Gettings

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