I say it is brittle because it has failed twice and both times quite spectacularly. Not only did the Inconel fail in the area adjacent to the welds but spider cracks formed flowing out of the main cracks and into the surrounding area. It looked like glass might look if you punch a hole in it (i.e. not tempered glass!).

 

It is the shape that is the problem. The cylinder is the second choice (ideal shape is the sphere) for containing pressure. Closing the ends with a flat sheet is the problem.

 

Even with the support of the exit tube in the center, it is hopeless to expect success. The only possible shape to close the ends is a hemispherical shape. 

 

The exact same failures occur to the expensive Mazda racing mufflers, even though you can stick your arm through them and they would seem to have no back pressure at all and are made of some sort of stainless. And even though they are mounted over 80 inches from the engine. The rotary just pounds them to death. Failing all of the end pieces beside each weld.

 

I tried one of the giant Flowmaster suitcase mufflers that the GT-1 Mustangs were using. Very heavy but made flat on the sides. (Looks like a suitcase) Even mounted at the rear of the car, it didn't make it through a weekend. It swelled up like a giant pillow and the baffles piled up in front of the 4" exit pipe. It got real quiet then and took the power down to about 50 HP.

 

You may have seen the big cast iron football looking afterburner on the early RX-2s and RX-3s.

If the air-pump were to quit, the guts would melt in that thing.

 

As you lean to lean of peak EGT for longer range and lower temps, you will pass through PEAK EGT. That could be well over 1800 degrees. When each exhaust pulse sees the big chamber it drops to subsonic and trades velocity for pressure. That sonic boom is what makes rotaries so loud. So you get the material into its worst strength situation and then beat on it with white hot hammers. The spider cracks are typical of high temperature fatigue.

 

So if you must have the muffler right next to the engine, the design is going to have to be very clever indeed to avoid 1/4" wall thickness materials. I have yet to see one I would bother to install.

 

Lynn E. Hanover