Well, I ran my 20B on Saturday, with and without the spiral-flow muffler insert, and took some sound measurements.  It looks like its good for about a 14db reduction at 3-4000 rpm.  Keep in mind that the a/c was positioned between two rows of hangars and since I have a prop now, a good part of the db numbers represent prop noise.  Measurements were taken at the front, rear, and at the wing tips, which is about 16’ from the exhaust for the left wing and 18’ for the right wing.  Never the less, I am pleased with the results.  After we finished the initial runs, I removed the insert and inspected it for damage… there was none.  I have 10 hours of easy running on it at this point.  The real test is yet to come.

 

Test data below…

Mark S.

 

 

R Wing
RPMS	Mode A	Mode C	Muffler Insert
1200	81	90	Y
1600	84	93	Y
4000	97	102	Y

 

Front
RPMS	Mode A	Mode C	Muffler Insert
1200	80	92	Y
1600	83	94	Y
3000	96	100	Y
4000	100	100	Y
1600	94	90	N
4000	111	114	N

 

Left Wing
RPMS	Mode A	Mode C	Muffler Insert
1200	82	92	Y
1600	83	93	Y
3000	90	102	Y
4000	96	104	Y
4000	111	114	N

 

Rear
RPMS	Mode A	Mode C	Muffler Insert
1200	82	93	Y
1600	83	104	Y
3000	96	112	Y