----- Original Message -----
Sent: Saturday, January 17, 2009 12:05 AM
Subject: [FlyRotary] DNA Muffler
Does anyone on the list have any real-life rotary experience with the DNA Gen II muffler (
http://www.dnamufflers.com/DNA/main_DNA.html)? It is an interesting design in that it has no packing material to burn out. Instead, it utilizes ladder-rungs, which they call "internal sound diffusers", which resemble a chain of DNA down through the center of the muffler body, which is made of 304 SS. Their web site claims that the racers use them with great success. From speaking with a sales rep, they claim there the rotary crowd uses them too. I'm considering purchasing one of their FULL THROTTLE COLLECTOR mufflers (P/N 1040), but thought I would check to see if anyone else has used this style muffler. This muffler has a 3" inlet/outlet with a 4" body. So it is compact enough to fit inside my cowl. My exhaust header has a 3" swivel joint, so it should be a good fit.
Mark S.
Mark,
From my calculations ( and from memory) 3" is fine, the length and diameter look fine and confirm my own calculations, however their not designed for the rotary specifically, I notice, and I'd be concerned about the thickness of the spiraled internals and believe they would have to be substantial, probably 1/8" to 3/16" thickness material - which makes for a heavy exhaust, but that's the trade-off for having it survive for a reasonable time. If it were to fail internally, it most certainly block the exhaust gases.
The trick is to have the correct volume; and restrict the exhaust sound waves from seeing the exit directly without restricting the gas flow.
Looking back on my notes I'm settled on a 3.5"- 4" exhaust for the 2 rotor and 3" for the single rotor. I've settled on 12" long for the single rotor and 15" long would be fine for the 2 rotor. I've made mine 5" internal and 6" external. So anywhere between the two is fine, just do some of your own calculations to confirm this.
George ( down under)