Mark/Ed/Bill,
I was thinking along the same lines as Bill - that the DNA is more restrictive resulting in richer mixtures at equivalent MAP. My home made muffler was a copy of the Moroso spiral flow mufflers, but with a larger center tube. With my home made muffler I can look all the way through it so the DNA is clearly more restrictive. Which is why I'm surprised it didnt work better.
The DNA sure looks better than my home made muffler. Weld quality is great. Time will tell how it holds up. The home made muffler was Inconel so I expect it would be more durable in the long run.
The point of something else in the airflow path limiting HP is a good point. One of things I've noticed is that I reach max power long before I reach max throttle. Since I'm making enough power for good performance I wasnt too worried about this, but I am curious. Once I reach about 3/4 throttle I'm maxed out - the last 1/4 doesnt do anything.
Mike Wills
RV-4 N144MW
The first problem to overcome when muffling a rotary, is the supersonic shock wave leaving the engine. If you can see through the muffler from end to end, it is probable that some part of that shock wave will exit the muffler. In order to slow the shock wave to subsonic it is required that the muffler provide some pressure in front of, Or, to impinge on the moving wave to slow it down.
The Mazda racing muffler has an empty room at the front that allows the shock wave to expand and drop to subsonic before muffling begins. You can see through the Mazda muffler, but they address the supersonic problem early in the process. They used to use lava rocks for the media, This stuff would be turned to dust and expelled during the year, and need to be replaced.
The center tube was perfed as was the front bulkhead. So pressure from the front chamber could see the center tube cross section
and the perfed bulkhead area. So in that regard the muffler was ineffective if the front chaomber failed to drop the shock wave to subsonic. However it did, and could hold the strongest Rotary to 105 dB at 50 feet. (Full throttle at best power RPM) Probably well above 9,000 RPM.
So to muffle you drop the velocity, using volume changes. By cooling the flow, by impinging on the flow with gasses collected in the front of the muffler and reintroduced near the end of the muffler, by using the flow to impinge on itself with splitters or divided flow tricks and reflectors. By absorbing the highest pressure peaks in some form of replaceable media. By absorbing the most offensive frequencies in tuned cavities.
Once the supersonic problem is delt with, conventional car mufflers are effective.
My first muffler attempt started with the center tube being from a house jack strut. About 1/8 wall probably 1010 steel. Large diameter holes in the first 5 inches to help replicate the Mazda cavity muffler. Then a bulkhead with 1/4" holes. Then a space of about 4" with no holes. Then thousands (it seemed like) of 1/8" holes in the rest of the tube length. I worked pretty well and then melted the center tube near the front. There was no media involved. About 30" overall.
The rotary is slightly more tolorant of back pressure than is suspected, and this may be used to impinge
on fuffling flow. At the exhause flange, there is a negative pressure well below ambient. A leak here draws cold air into the system and unburned fuel ignites with a popping sound, like a 2 cycle scooter off the power.
Perf tube mufflers take off the peaks and then impinge on the flow. So they may affect tuning every where, and then change as the media melts into little balls or is hammered to dust and leaves the muffler.
It seemed to me that the Spintech was close to the best for this application, and would like to have seen that run to destruction.
Just my opinion, I could be completly wrong.
Lynn E. Hanover