Hit reply and not send text. The picture , attachment ,
is what I tried to explain about drilling then bending the flare
in with a punch or something. The inner scoop catches the
hot gasses to start them out and the outer flare provides a small
vacuum to help. Total area equals pipe diameter and is
spread out over a longer distance helps quiet the BANGS.
Virg. WHEUW!

"Bass, Jerry" wrote:

I just tried two short (4.5") fishtails with 3/16 slot and 4.31 wide.  86
i/8" holes.  No apparent improvement.  I could hear some Wiz-ing under my
feet, though.  The extensions apparently cause some buzzing.

Jerry Bass

That is interesting. Are the lips on the fish tail vibrating? The P51's have beefed up lips.
Are the holes in the fish tails themselves or in a pipe leading up to the fish tails?

Jerry, are you willing to pop $80 for a Radio Shack sound (db) meter?
If you get one stand 30 feet away along side the engine while running it
up to static RPM and let us know what the RPM and the reading is on the 
"slow" A scale (as I recall). I published some numbers back in 
December for Tracy's airplane before his bullet muffler failed.

I'll be sure to bring my db meter to Sun & Fun so we can have
a little muffler competition :-)

Paul Lamar
 
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