Thanks Lynn. Do you remember the relative density/spacing/size of the perf?

Since they were Japanese it would have been metric, maybe 3/16"

My Borla has 5 rolled perf tubes in a bundle pressed into the 4" perf
tube through the center. About 26" long and 7 1/2" in diameter. If it
had stuffing in it new it doesn't now. I read somewhere that high
frequency sound
traveled along the outside of systems. So I added a sheet stock ring
just under 1/2" tall into the end of the pipe just after the muffler.
Seemed to make a difference so I left it in. We needed 103 dB max and
have been as low as 97 dB. Full throttle loaded at 50 feet.

I tried a 1 1/4" by 1/4" thick puck in the center of the flow at the end
of the muffler. It did cut the noise down, but the driver whined about
being down on power. It was not a factor in lap times, but if the driver
thinks its slower it will be eventually. The heat tape has been in place
for 5 years with no damage.

Lynn E. Hanover

Lynn, regarding your drawing of the open chamber muffler, were there also
perforations in the transverse bulkhead plate at the aft end of the
expansion chamber (supporting the front end of the perforated main tube)?
You should get an award for keeping that heat tape on for that long.

Steve Beckhamn


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