>
 > I did the collapsed muffler deal at Sebring years back. The
 > Flowmaster (big suitcase looking thing) had all of the baffles
 > piled up against the rear outlet. The muffler swelled up like a
 > giant pillow and the power dropped off to nearly nothing. It
 > didn't hurt the engine at all and we raced at West Palm Beach the
 > next weekend.
 >
 > Looking at the Mistral muffler, I am struck by the tubes with holes
 > right at the flange. There is no way this didn't cost them big HP.
 > The rotary is a 4 stroke Otto cycle engine but it tunes like a 2
 > stroke dirt bike.
 > So a bit of a run out of the engine before you do anything to the
 > flow will be better than anything. So, as long a tube as is possible
 > straight out of the port. Then either a long run to the collector if
 > possible in very thick walled tubing or make the first turn in each
 > tube a slip joint. For a long system there is a need to support the
 > tubes solid to the engine, if the engine can move. If the engine can
 > move you cannot clamp the tubing to a structure that does not move
 > with the engine.
 >
 > One system I like for space and simplicity is a short system. Maybe
 > 10"-11" right into a collector. The first 3"-4" inches is straight
 > out of the port, and the curves into the collector have duplicates
 > of the stubs as long slip joints. These need not be exotic balls or
 > bellows. Just a joint that cannot transfer very much motion into the
 > tubing. The header is held to the stubs with stiff springs. The
 > springs have safety wire run through them, so if one should fail,
 > the header still cannot escape, and the pieces of broken spring are
 > retained. This is to allow for shape changes in the collector as the
 > out walls of the curved surface operate at higher temps than the
 > inner walls. Any leaks in the supersonic portion of the exhaust
 > result in air entering at the leak point. I have no gasket at the
 > flange, Just GE silicone. Air entering the system will get you
 > a popping sound on closed throttle. If you have way too much back
 > pressure for a rotary, you could get an exhaust leak, but the power
 > will be way down.
 >
 > The Mazda racing muffler give you some ideas, that might help. A 4"
 > diameter tube through about a 10" diameter tube about 12" long.
 > looks like a short fat glass packed muffler. The core has the
 > standard perf tube but at the front end, the core stops with a
 > bulkhead of perf stainless and an open room with the perf tube
 > stopping at the perf bulkhead. So, there is a gap of about 3" in the
 > tube through the muffler. In this room, I suspect that there
 > supersonic flow drops to subsonic. They had a very nice sound,
 > rather unlike a rotary. They were expensive and lasted about one
 > season. Depending on how fast the car was. (HP used?). The muffler
 > mounted under the rear bumper.
 > So, heat was less a factor than the pounding. I don't know if they
 > had any kind of packing at all.
 >
 > The ends were round but flat. Failure would be the whole muffler
 > falling off leaving the front end on the tube. Or, the rear bulkhead
 > and exit tube falling off.
 >
 > One rule is that if it is flat it dies. The closer it is to the
 > engine, the sooner it will die.
 >
 > Another rule might be, that if the engine moves, you must have a
 > slip joint close to the engine. Even if the exhaust system is soft
 > mounted. On race cars the exhaust systems have a saddle supporting
 > that last length of tubing. A half of a larger tube, with a screen
 > door spring over the top half, so the length can change with
 > temperature.
 >
 > I have several sets of Indy car headers in Inconel. At $10,000 a
 > set, why do you have them you might ask?
 >
 > I bought them at an annual automotive barn sale at the fairgrounds.
 > I paid $30.00 for a set on Saturday and Sunday just before closing I
 > bought the remaining 3 sets and some waste gate headers for $15.00.
 >
 > They are from Rahal (before Letterman) here in town. The man selling
 > them made the trophies for CART.
 >
 > He said they use these for three heat cycles and throw them into the
 > dumpster. They used to build their own, but found the man in England
 > who builds most of them for others and they just get three sets a
 > week from him.
 >
 > They cannot afford to blow in a million on a race weekend and
 > loose finish positions to a cracked header.
 >
 > And, Inconel cracks just like carbon steel, just at a higher
 > temperature. It does not tolerate poor design or workmanship.
 >
 > In this picture the engine flanges are castings with the tubing welded
 > to them. The whole thing is a work of art. There are no bends here. They
 > are made from little flat sheets rolled into shape and welded. The weld
 > beads are nearly invisible. So little stretching is involved. The
 > material is very thin and the header set half the weight of a carbon
 > steel set.
 > The strange thing at the left is made of stainless rectangular tubing
 > and is the waste gate exhaust header.
 > It is flat, to fit between the rear tire and the bodywork. They have
 > machined off the tabs on the header set, used to hold the sections
 > together. A tab on each tube with a short piece of sheet stock between
 > and two bolts. The bolts are not tightened and allowed to spin and
 > vibrate at high RPM. They deform the bolts so no safety wire is
 > required. You can see two such links on the waste gate header.
 >
 > I can produce simple picture in MS Paint if that could help anyone.
 >
 > Lynn E. Hanover
 >
 > Paul, and Lynn H., I would like to see some pics of this type of
 > exhaust. Thanks, Dave D.
 >
 > Here is what I remember.
 >
 > Lynn E. Hanover
 >
 > Better make the guts out of 1/8 inch thick 321 SS :)
 >
 > --
 > Paul Lamar ...No rotor no motor.

Since even Iconel steel wilts before the blast of a rotary exhaust, can
the part of the exhaust that channels the hot gasses be made of
ceramics, which can better stand the heat?

Les Nordman

I would not exactly say that Les :)

There are Inconel mufflers on rotary engines with hundreds of hours.
Here is one on Steve Mcgowans gyro.

Other people have used 3/16th thick 321 SS and it hardly discolors.

It is a weight trade off. Low weight cost money. How light do you want
it to be?