The rule is that short collectors tune over a small range of RPM. Long collectors tune over a broad range of RPM. Note that in racing systems, you always see the tubes entering the collector with all of the tubes having been run in parallel for some distance. The collectors will be 4 to 8 tube diameters long.
Cutting off the short collector and adding material to increase the overall length to come out to 6 to 8 tube diameters was what I was trying to get across. Flow is supersonic in the rotary exhaust flow and errors in construction can cause profound outcomes. So make it smooth inside. The flow slowing to subsonic inside the muffler creates the many sound control problems. I was interested in the Spintec because of the many turning vanes holding the flat sides together may have extended its life. Otherwise only round mufflers survive for very long. Round is not a good shape for aircraft use. Stainless swarf filled stainless mufflers hold up the longest.
The 4" pipe in the picture was later turned down to face the track when readings exceeded 103 dB.
Lynn E. Hanover
In a message dated 5/19/2008 9:10:24 AM Eastern Daylight Time, keltro@att.net writes:
Doug,
Lynn suggested that you cut through the collector half way down and
extend its length about 1/3.........What is not clear to me is if the cut and
extension would be on the inlet or outlet of the collector ?? Why add an
extension in the middle of the collector ?? Why not at the end of the outlet
if that is where he is saying it should be added ?? Am I not seeing the big
picture here ??
--
Kelly Troyer